curl/docs/libcurl/curl_easy_setopt.3

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.TH curl_easy_setopt 3 "1 Jan 2010" "libcurl 7.20.0" "libcurl Manual"
.SH NAME
curl_easy_setopt \- set options for a curl easy handle
.SH SYNOPSIS
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLoption option, parameter);
.SH DESCRIPTION
curl_easy_setopt() is used to tell libcurl how to behave. By using the
appropriate options to \fIcurl_easy_setopt\fP, you can change libcurl's
behavior.  All options are set with the \fIoption\fP followed by a
\fIparameter\fP. That parameter can be a \fBlong\fP, a \fBfunction pointer\fP,
an \fBobject pointer\fP or a \fBcurl_off_t\fP, depending on what the specific
option expects. Read this manual carefully as bad input values may cause
libcurl to behave badly!  You can only set one option in each function call. A
typical application uses many curl_easy_setopt() calls in the setup phase.

Options set with this function call are valid for all forthcoming transfers
performed using this \fIhandle\fP.  The options are not in any way reset
between transfers, so if you want subsequent transfers with different options,
you must change them between the transfers. You can optionally reset all
options back to internal default with \fIcurl_easy_reset(3)\fP.

Strings passed to libcurl as 'char *' arguments, are copied by the library;
thus the string storage associated to the pointer argument may be overwritten
after curl_easy_setopt() returns. Exceptions to this rule are described in
the option details below.

Before version 7.17.0, strings were not copied. Instead the user was forced
keep them available until libcurl no longer needed them.

The \fIhandle\fP is the return code from a \fIcurl_easy_init(3)\fP or
\fIcurl_easy_duphandle(3)\fP call.
.SH BEHAVIOR OPTIONS
.IP CURLOPT_VERBOSE
Set the parameter to 1 to get the library to display a lot of verbose
information about its operations. Very useful for libcurl and/or protocol
debugging and understanding. The verbose information will be sent to stderr,
or the stream set with \fICURLOPT_STDERR\fP. The default value for this
parameter is 0.

You hardly ever want this set in production use, you will almost always want
this when you debug/report problems. Another neat option for debugging is the
\fICURLOPT_DEBUGFUNCTION\fP.
.IP CURLOPT_HEADER
A parameter set to 1 tells the library to include the header in the body
output. This is only relevant for protocols that actually have headers
preceding the data (like HTTP). The default value for this parameter is 0.
.IP CURLOPT_NOPROGRESS
Pass a long. If set to 1, it tells the library to shut off the progress meter
completely. It will also prevent the \fICURLOPT_PROGRESSFUNCTION\fP from
getting called. The default value for this parameter is 1.

Future versions of libcurl are likely to not have any built-in progress meter
at all.
.IP CURLOPT_NOSIGNAL
Pass a long. If it is 1, libcurl will not use any functions that
install signal handlers or any functions that cause signals to be sent to the
process. This option is mainly here to allow multi-threaded unix applications
to still set/use all timeout options etc, without risking getting signals.
The default value for this parameter is 0.
(Added in 7.10)

If this option is set and libcurl has been built with the standard name
resolver, timeouts will not occur while the name resolve takes place.
Consider building libcurl with c-ares support to enable asynchronous DNS
lookups, which enables nice timeouts for name resolves without signals.

Setting \fICURLOPT_NOSIGNAL\fP to 1 makes libcurl NOT ask the system to ignore
SIGPIPE signals, which otherwise are sent by the system when trying to send
data to a socket which is closed in the other end. libcurl makes an effort to
never cause such SIGPIPEs to trigger, but some operating systems have no way
to avoid them and even on those that have there are some corner cases when
they may still happen, contrary to our desire. In addition, using
\fICURLAUTH_NTLM_WB\fP authentication could cause a SIGCHLD signal to be
raised.
.IP CURLOPT_WILDCARDMATCH
Set this option to 1 if you want to transfer multiple files according to a
file name pattern. The pattern can be specified as part of the
\fICURLOPT_URL\fP option, using an fnmatch-like pattern (Shell Pattern
Matching) in the last part of URL (file name).

By default, libcurl uses its internal wildcard matching implementation. You
can provide your own matching function by the \fICURLOPT_FNMATCH_FUNCTION\fP
option.

This feature is only supported by the FTP download for now.

A brief introduction of its syntax follows:
.RS
.IP "* - ASTERISK"
\&ftp://example.com/some/path/\fB*.txt\fP (for all txt's from the root
directory)
.RE
.RS
.IP "? - QUESTION MARK"
Question mark matches any (exactly one) character.

\&ftp://example.com/some/path/\fBphoto?.jpeg\fP
.RE
.RS
.IP "[ - BRACKET EXPRESSION"
The left bracket opens a bracket expression. The question mark and asterisk have
no special meaning in a bracket expression. Each bracket expression ends by the
right bracket and matches exactly one character. Some examples follow:

\fB[a-zA-Z0\-9]\fP or \fB[f\-gF\-G]\fP \- character interval

\fB[abc]\fP - character enumeration

\fB[^abc]\fP or \fB[!abc]\fP - negation

\fB[[:\fP\fIname\fP\fB:]]\fP class expression. Supported classes are
\fBalnum\fP,\fBlower\fP, \fBspace\fP, \fBalpha\fP, \fBdigit\fP, \fBprint\fP,
\fBupper\fP, \fBblank\fP, \fBgraph\fP, \fBxdigit\fP.

\fB[][-!^]\fP - special case \- matches only '\-', ']', '[', '!' or '^'. These
characters have no special purpose.

\fB[\\[\\]\\\\]\fP - escape syntax. Matches '[', ']' or '\\'.

Using the rules above, a file name pattern can be constructed:

\&ftp://example.com/some/path/\fB[a-z[:upper:]\\\\].jpeg\fP
.RE
.PP
(This was added in 7.21.0)
.SH CALLBACK OPTIONS
.IP CURLOPT_WRITEFUNCTION
Pass a pointer to a function that matches the following prototype:
\fBsize_t function( char *ptr, size_t size, size_t nmemb, void *userdata);\fP
This function gets called by libcurl as soon as there is data received that
needs to be saved. The size of the data pointed to by \fIptr\fP is \fIsize\fP
multiplied with \fInmemb\fP, it will not be zero terminated. Return the number
of bytes actually taken care of. If that amount differs from the amount passed
to your function, it'll signal an error to the library. This will abort the
transfer and return \fICURLE_WRITE_ERROR\fP.

From 7.18.0, the function can return CURL_WRITEFUNC_PAUSE which then will
cause writing to this connection to become paused. See
\fIcurl_easy_pause(3)\fP for further details.

This function may be called with zero bytes data if the transferred file is
empty.

Set this option to NULL to get the internal default function. The internal
default function will write the data to the FILE * given with
\fICURLOPT_WRITEDATA\fP.

Set the \fIuserdata\fP argument with the \fICURLOPT_WRITEDATA\fP option.

The callback function will be passed as much data as possible in all invokes,
but you cannot possibly make any assumptions. It may be one byte, it may be
thousands. The maximum amount of body data that can be passed to the write
callback is defined in the curl.h header file: CURL_MAX_WRITE_SIZE (the usual
default is 16K). If you however have \fICURLOPT_HEADER\fP set, which sends
header data to the write callback, you can get up to
\fICURL_MAX_HTTP_HEADER\fP bytes of header data passed into it. This usually
means 100K.
.IP CURLOPT_WRITEDATA
Data pointer to pass to the file write function. If you use the
\fICURLOPT_WRITEFUNCTION\fP option, this is the pointer you'll get as
input. If you don't use a callback, you must pass a 'FILE *' (cast
to 'void *') as libcurl will pass this to fwrite() when writing data.
By default, the value of this parameter is unspecified.

The internal \fICURLOPT_WRITEFUNCTION\fP will write the data to the FILE *
given with this option, or to stdout if this option hasn't been set.

If you're using libcurl as a win32 DLL, you \fBMUST\fP use the
\fICURLOPT_WRITEFUNCTION\fP if you set this option or you will experience
crashes.

This option is also known with the older name \fICURLOPT_FILE\fP, the name
\fICURLOPT_WRITEDATA\fP was introduced in 7.9.7.
.IP CURLOPT_READFUNCTION
Pass a pointer to a function that matches the following prototype:
\fBsize_t function( void *ptr, size_t size, size_t nmemb, void *userdata);\fP
This function gets called by libcurl as soon as it needs to read data in order
to send it to the peer. The data area pointed at by the pointer \fIptr\fP may
be filled with at most \fIsize\fP multiplied with \fInmemb\fP number of
bytes. Your function must return the actual number of bytes that you stored in
that memory area. Returning 0 will signal end-of-file to the library and cause
it to stop the current transfer.

If you stop the current transfer by returning 0 "pre-maturely" (i.e before the
server expected it, like when you've said you will upload N bytes and you
upload less than N bytes), you may experience that the server "hangs" waiting
for the rest of the data that won't come.

The read callback may return \fICURL_READFUNC_ABORT\fP to stop the current
operation immediately, resulting in a \fICURLE_ABORTED_BY_CALLBACK\fP error
code from the transfer (Added in 7.12.1)

From 7.18.0, the function can return CURL_READFUNC_PAUSE which then will cause
reading from this connection to become paused. See \fIcurl_easy_pause(3)\fP
for further details.

\fBBugs\fP: when doing TFTP uploads, you must return the exact amount of data
that the callback wants, or it will be considered the final packet by the
server end and the transfer will end there.

If you set this callback pointer to NULL, or don't set it at all, the default
internal read function will be used. It is doing an fread() on the FILE *
userdata set with \fICURLOPT_READDATA\fP.
.IP CURLOPT_READDATA
Data pointer to pass to the file read function. If you use the
\fICURLOPT_READFUNCTION\fP option, this is the pointer you'll get as input. If
you don't specify a read callback but instead rely on the default internal
read function, this data must be a valid readable FILE * (cast to 'void *').

If you're using libcurl as a win32 DLL, you MUST use a
\fICURLOPT_READFUNCTION\fP if you set this option.

This option was also known by the older name \fICURLOPT_INFILE\fP, the name
\fICURLOPT_READDATA\fP was introduced in 7.9.7.
.IP CURLOPT_IOCTLFUNCTION
Pass a pointer to a function that matches the following prototype:
\fBcurlioerr function(CURL *handle, int cmd, void *clientp);\fP. This function
gets called by libcurl when something special I/O-related needs to be done
that the library can't do by itself. For now, rewinding the read data stream
is the only action it can request. The rewinding of the read data stream may
be necessary when doing a HTTP PUT or POST with a multi-pass authentication
method. By default, this parameter is set to NULL.  (Option added in 7.12.3).

Use \fICURLOPT_SEEKFUNCTION\fP instead to provide seeking! If
\fICURLOPT_SEEKFUNCTION\fP is set, this parameter will be ignored when seeking.
.IP CURLOPT_IOCTLDATA
Pass a pointer that will be untouched by libcurl and passed as the 3rd
argument in the ioctl callback set with \fICURLOPT_IOCTLFUNCTION\fP.
By default, the value of this parameter is unspecified.  (Option added in
7.12.3)
.IP CURLOPT_SEEKFUNCTION
Pass a pointer to a function that matches the following prototype: \fBint
function(void *instream, curl_off_t offset, int origin);\fP This function gets
called by libcurl to seek to a certain position in the input stream and can be
used to fast forward a file in a resumed upload (instead of reading all
uploaded bytes with the normal read function/callback). It is also called to
rewind a stream when doing a HTTP PUT or POST with a multi-pass authentication
method. The function shall work like "fseek" or "lseek" and accepted SEEK_SET,
SEEK_CUR and SEEK_END as argument for origin, although libcurl currently only
passes SEEK_SET. The callback must return 0 (CURL_SEEKFUNC_OK) on success, 1
(CURL_SEEKFUNC_FAIL) to cause the upload operation to fail or 2
(CURL_SEEKFUNC_CANTSEEK) to indicate that while the seek failed, libcurl is
free to work around the problem if possible. The latter can sometimes be done
by instead reading from the input or similar.

By default, this parameter is unset.

If you forward the input arguments directly to "fseek" or "lseek", note that
the data type for \fIoffset\fP is not the same as defined for curl_off_t on
many systems! (Option added in 7.18.0)
.IP CURLOPT_SEEKDATA
Data pointer to pass to the file seek function. If you use the
\fICURLOPT_SEEKFUNCTION\fP option, this is the pointer you'll get as input. If
you don't specify a seek callback, NULL is passed. (Option added in 7.18.0)
.IP CURLOPT_SOCKOPTFUNCTION
Pass a pointer to a function that matches the following prototype: \fBint
function(void *clientp, curl_socket_t curlfd, curlsocktype purpose);\fP. By
default, this parameter is unset. If set, this
function gets called by libcurl after the socket() call but before the
connect() call. The callback's \fIpurpose\fP argument identifies the exact
purpose for this particular socket:

\fICURLSOCKTYPE_IPCXN\fP for actively created connections or since 7.28.0
\fICURLSOCKTYPE_ACCEPT\fP for FTP when the connection was setup with PORT/EPSV
(in earlier versions these sockets weren't passed to this callback).

Future versions of libcurl may support more purposes. It passes the newly
created socket descriptor so additional setsockopt() calls can be done at the
user's discretion.  Return 0 (zero) from the callback on success. Return 1
from the callback function to signal an unrecoverable error to the library and
it will close the socket and return \fICURLE_COULDNT_CONNECT\fP.  (Option
added in 7.16.0)

Added in 7.21.5, the callback function may return
\fICURL_SOCKOPT_ALREADY_CONNECTED\fP, which tells libcurl that the socket is
in fact already connected and then libcurl will not attempt to connect it.
.IP CURLOPT_SOCKOPTDATA
Pass a pointer that will be untouched by libcurl and passed as the first
argument in the sockopt callback set with \fICURLOPT_SOCKOPTFUNCTION\fP.
The default value of this parameter is unspecified.
(Option added in 7.16.0)
.IP CURLOPT_OPENSOCKETFUNCTION
Pass a pointer to a function that matches the following prototype:
\fBcurl_socket_t function(void *clientp, curlsocktype purpose, struct
curl_sockaddr *address);\fP. This function gets called by libcurl instead of
the \fIsocket(2)\fP call. The callback's \fIpurpose\fP argument identifies the
exact purpose for this particular socket: \fICURLSOCKTYPE_IPCXN\fP is for IP
based connections. Future versions of libcurl may support more purposes. It
passes the resolved peer address as a \fIaddress\fP argument so the callback
can modify the address or refuse to connect at all. The callback function
should return the socket or \fICURL_SOCKET_BAD\fP in case no connection could
be established or another error was detected. Any additional
\fIsetsockopt(2)\fP calls can be done on the socket at the user's discretion.
\fICURL_SOCKET_BAD\fP return value from the callback function will signal an
unrecoverable error to the library and it will return
\fICURLE_COULDNT_CONNECT\fP.  This return code can be used for IP address
blacklisting.  The default behavior is:
.nf
   return socket(addr->family, addr->socktype, addr->protocol);
.fi
(Option added in 7.17.1.)
.IP CURLOPT_OPENSOCKETDATA
Pass a pointer that will be untouched by libcurl and passed as the first
argument in the opensocket callback set with \fICURLOPT_OPENSOCKETFUNCTION\fP.
The default value of this parameter is unspecified.
(Option added in 7.17.1.)
.IP CURLOPT_CLOSESOCKETFUNCTION
Pass a pointer to a function that matches the following prototype: \fBint
function(void *clientp, curl_socket_t item);\fP. This function gets called by
libcurl instead of the \fIclose(3)\fP or \fIclosesocket(3)\fP call when
sockets are closed (not for any other file descriptors). This is pretty much
the reverse to the \fICURLOPT_OPENSOCKETFUNCTION\fP option. Return 0 to signal
success and 1 if there was an error.  (Option added in 7.21.7)
.IP CURLOPT_CLOSESOCKETDATA
Pass a pointer that will be untouched by libcurl and passed as the first
argument in the closesocket callback set with
\fICURLOPT_CLOSESOCKETFUNCTION\fP.
The default value of this parameter is unspecified.
(Option added in 7.21.7)
.IP CURLOPT_PROGRESSFUNCTION
Pass a pointer to a function that matches the following prototype:

\fBint function(void *clientp, double dltotal, double dlnow, double ultotal,
double ulnow);\fP

We encourage users to use \fICURLOPT_XFERINFOFUNCTION\fP instead, if you can.

This function gets called by libcurl instead of its internal equivalent with a
frequent interval. While data is being transferred it will be called very
frequently, and during slow periods like when nothing is being transferred it
can slow down to about one call per second.

\fIclientp\fP is the pointer set with \fICURLOPT_PROGRESSDATA\fP, it is not
actually used by libcurl but is only passed along from the application to the
callback.

The callback gets told how much data libcurl will transfer and has
transferred, in number of bytes. \fIdltotal\fP is the total number of bytes
libcurl expects to download in this transfer. \fIdlnow\fP is the number of
bytes downloaded so far. \fIultotal\fP is the total number of bytes libcurl
expects to upload in this transfer. \fIulnow\fP is the number of bytes
uploaded so far.

Unknown/unused argument values passed to the callback will be set to zero
(like if you only download data, the upload size will remain 0). Many times
the callback will be called one or more times first, before it knows the data
sizes so a program must be made to handle that.

Returning a non-zero value from this callback will cause libcurl to abort the
transfer and return \fICURLE_ABORTED_BY_CALLBACK\fP.

If you transfer data with the multi interface, this function will not be
called during periods of idleness unless you call the appropriate libcurl
function that performs transfers.

\fICURLOPT_NOPROGRESS\fP must be set to 0 to make this function actually
get called.
.IP CURLOPT_XFERINFOFUNCTION
Pass a pointer to a function that matches the following prototype:

.nf
\fBint function(void *clientp, curl_off_t dltotal, curl_off_t dlnow,
                curl_off_t ultotal, curl_off_t ulnow);\fP
.fi

This function gets called by libcurl instead of its internal equivalent with a
frequent interval. While data is being transferred it will be called very
frequently, and during slow periods like when nothing is being transferred it
can slow down to about one call per second.

\fIclientp\fP is the pointer set with \fICURLOPT_XFERINFODATA\fP, it is only
passed along from the application to the callback.

The callback gets told how much data libcurl will transfer and has
transferred, in number of bytes. \fIdltotal\fP is the total number of bytes
libcurl expects to download in this transfer. \fIdlnow\fP is the number of
bytes downloaded so far. \fIultotal\fP is the total number of bytes libcurl
expects to upload in this transfer. \fIulnow\fP is the number of bytes
uploaded so far.

Unknown/unused argument values passed to the callback will be set to zero
(like if you only download data, the upload size will remain 0). Many times
the callback will be called one or more times first, before it knows the data
sizes so a program must be made to handle that.

Returning a non-zero value from this callback will cause libcurl to abort the
transfer and return \fICURLE_ABORTED_BY_CALLBACK\fP.

If you transfer data with the multi interface, this function will not be
called during periods of idleness unless you call the appropriate libcurl
function that performs transfers.

\fICURLOPT_NOPROGRESS\fP must be set to 0 to make this function actually
get called.

(Added in 7.32.0)
.IP CURLOPT_PROGRESSDATA
Pass a pointer that will be untouched by libcurl and passed as the first
argument in the progress callback set with \fICURLOPT_PROGRESSFUNCTION\fP.
The default value of this parameter is unspecified.
.IP CURLOPT_XFERINFODATA
Pass a pointer that will be untouched by libcurl and passed as the first
argument in the progress callback set with \fICURLOPT_XFERINFOFUNCTION\fP.
The default value of this parameter is unspecified. This option is an alias
for CURLOPT_PROGRESSDATA. (Added in 7.32.0)
.IP CURLOPT_HEADERFUNCTION
Pass a pointer to a function that matches the following prototype:
\fBsize_t function( void *ptr, size_t size, size_t nmemb, void
*userdata);\fP. This function gets called by libcurl as soon as it has
received header data. The header callback will be called once for each header
and only complete header lines are passed on to the callback. Parsing headers
is very easy using this. The size of the data pointed to by \fIptr\fP is
\fIsize\fP multiplied with \fInmemb\fP. Do not assume that the header line is
zero terminated! The pointer named \fIuserdata\fP is the one you set with the
\fICURLOPT_WRITEHEADER\fP option. The callback function must return the number
of bytes actually taken care of. If that amount differs from the amount passed
to your function, it'll signal an error to the library. This will abort the
transfer and return \fICURL_WRITE_ERROR\fP.

A complete HTTP header that is passed to this function can be up to
\fICURL_MAX_HTTP_HEADER\fP (100K) bytes.

If this option is not set, or if it is set to NULL, but
\fICURLOPT_HEADERDATA\fP (\fICURLOPT_WRITEHEADER\fP) is set to anything but
NULL, the function used to accept response data will be used instead. That is,
it will be the function specified with \fICURLOPT_WRITEFUNCTION\fP, or if it
is not specified or NULL - the default, stream-writing function.

It's important to note that the callback will be invoked for the headers of
all responses received after initiating a request and not just the final
response. This includes all responses which occur during authentication
negotiation. If you need to operate on only the headers from the final
response, you will need to collect headers in the callback yourself and use
HTTP status lines, for example, to delimit response boundaries.

When a server sends a chunked encoded transfer, it may contain a trailer. That
trailer is identical to a HTTP header and if such a trailer is received it is
passed to the application using this callback as well. There are several ways
to detect it being a trailer and not an ordinary header: 1) it comes after the
response-body. 2) it comes after the final header line (CR LF) 3) a Trailer:
header among the regular response-headers mention what header(s) to expect in
the trailer.

For non-HTTP protocols like FTP, POP3, IMAP and SMTP this function will get
called with the server responses to the commands that libcurl sends.
.IP CURLOPT_WRITEHEADER
(This option is also known as \fBCURLOPT_HEADERDATA\fP) Pass a pointer to be
used to write the header part of the received data to. If you don't use
\fICURLOPT_WRITEFUNCTION\fP or \fICURLOPT_HEADERFUNCTION\fP to take care of
the writing, this must be a valid FILE * as the internal default will then be
a plain fwrite(). See also the \fICURLOPT_HEADERFUNCTION\fP option above on
how to set a custom get-all-headers callback.
.IP CURLOPT_DEBUGFUNCTION
Pass a pointer to a function that matches the following prototype: \fBint
curl_debug_callback (CURL *, curl_infotype, char *, size_t, void *);\fP
\fICURLOPT_DEBUGFUNCTION\fP replaces the standard debug function used when
\fICURLOPT_VERBOSE \fP is in effect. This callback receives debug information,
as specified with the \fBcurl_infotype\fP argument. This function must return
0.  The data pointed to by the char * passed to this function WILL NOT be zero
terminated, but will be exactly of the size as told by the size_t argument.

Available curl_infotype values:
.RS
.IP CURLINFO_TEXT
The data is informational text.
.IP CURLINFO_HEADER_IN
The data is header (or header-like) data received from the peer.
.IP CURLINFO_HEADER_OUT
The data is header (or header-like) data sent to the peer.
.IP CURLINFO_DATA_IN
The data is protocol data received from the peer.
.IP CURLINFO_DATA_OUT
The data is protocol data sent to the peer.
.IP CURLINFO_SSL_DATA_OUT
The data is SSL/TLS (binary) data sent to the peer.
.IP CURLINFO_SSL_DATA_IN
The data is SSL/TLS (binary) data received from the peer.
.RE
.IP CURLOPT_DEBUGDATA
Pass a pointer to whatever you want passed in to your
\fICURLOPT_DEBUGFUNCTION\fP in the last void * argument. This pointer is not
used by libcurl, it is only passed to the callback.
.IP CURLOPT_SSL_CTX_FUNCTION
This option does only function for libcurl powered by OpenSSL. If libcurl was
built against another SSL library, this functionality is absent.

Pass a pointer to a function that matches the following prototype:
\fBCURLcode sslctxfun(CURL *curl, void *sslctx, void *parm);\fP This function
gets called by libcurl just before the initialization of a SSL connection
after having processed all other SSL related options to give a last chance to
an application to modify the behaviour of openssl's ssl initialization. The
\fIsslctx\fP parameter is actually a pointer to an openssl \fISSL_CTX\fP. If
an error is returned no attempt to establish a connection is made and the
perform operation will return the error code from this callback function.  Set
the \fIparm\fP argument with the \fICURLOPT_SSL_CTX_DATA\fP option. This
option was introduced in 7.11.0.

This function will get called on all new connections made to a server, during
the SSL negotiation. The SSL_CTX pointer will be a new one every time.

To use this properly, a non-trivial amount of knowledge of the openssl
libraries is necessary. For example, using this function allows you to use
openssl callbacks to add additional validation code for certificates, and even
to change the actual URI of a HTTPS request (example used in the lib509 test
case).  See also the example section for a replacement of the key, certificate
and trust file settings.
.IP CURLOPT_SSL_CTX_DATA
Data pointer to pass to the ssl context callback set by the option
\fICURLOPT_SSL_CTX_FUNCTION\fP, this is the pointer you'll get as third
parameter, otherwise \fBNULL\fP. (Added in 7.11.0)
.IP CURLOPT_CONV_TO_NETWORK_FUNCTION
.IP CURLOPT_CONV_FROM_NETWORK_FUNCTION
.IP CURLOPT_CONV_FROM_UTF8_FUNCTION
Pass a pointer to a function that matches the following prototype:
\fBCURLcode function(char *ptr, size_t length);\fP

These three options apply to non-ASCII platforms only.  They are available
only if \fBCURL_DOES_CONVERSIONS\fP was defined when libcurl was built. When
this is the case, \fIcurl_version_info(3)\fP will return the CURL_VERSION_CONV
feature bit set.

The data to be converted is in a buffer pointed to by the ptr parameter.  The
amount of data to convert is indicated by the length parameter.  The converted
data overlays the input data in the buffer pointed to by the ptr parameter.
CURLE_OK should be returned upon successful conversion.  A CURLcode return
value defined by curl.h, such as CURLE_CONV_FAILED, should be returned if an
error was encountered.

\fBCURLOPT_CONV_TO_NETWORK_FUNCTION\fP and
\fBCURLOPT_CONV_FROM_NETWORK_FUNCTION\fP convert between the host encoding and
the network encoding.  They are used when commands or ASCII data are
sent/received over the network.

\fBCURLOPT_CONV_FROM_UTF8_FUNCTION\fP is called to convert from UTF8 into the
host encoding.  It is required only for SSL processing.

If you set a callback pointer to NULL, or don't set it at all, the built-in
libcurl iconv functions will be used.  If HAVE_ICONV was not defined when
libcurl was built, and no callback has been established, conversion will
return the CURLE_CONV_REQD error code.

If HAVE_ICONV is defined, CURL_ICONV_CODESET_OF_HOST must also be defined.
For example:

 \&#define CURL_ICONV_CODESET_OF_HOST "IBM-1047"

The iconv code in libcurl will default the network and UTF8 codeset names as
follows:

 \&#define CURL_ICONV_CODESET_OF_NETWORK "ISO8859-1"

 \&#define CURL_ICONV_CODESET_FOR_UTF8   "UTF-8"

You will need to override these definitions if they are different on your
system.
.IP CURLOPT_INTERLEAVEFUNCTION
Pass a pointer to a function that matches the following prototype:
\fBsize_t function( void *ptr, size_t size, size_t nmemb, void
*userdata)\fP. This function gets called by libcurl as soon as it has received
interleaved RTP data. This function gets called for each $ block and therefore
contains exactly one upper-layer protocol unit (e.g.  one RTP packet). Curl
writes the interleaved header as well as the included data for each call. The
first byte is always an ASCII dollar sign. The dollar sign is followed by a
one byte channel identifier and then a 2 byte integer length in network byte
order. See \fIRFC2326 Section 10.12\fP for more information on how RTP
interleaving behaves. If unset or set to NULL, curl will use the default write
function.

Interleaved RTP poses some challenges for the client application. Since the
stream data is sharing the RTSP control connection, it is critical to service
the RTP in a timely fashion. If the RTP data is not handled quickly,
subsequent response processing may become unreasonably delayed and the
connection may close. The application may use \fICURL_RTSPREQ_RECEIVE\fP to
service RTP data when no requests are desired. If the application makes a
request, (e.g.  \fICURL_RTSPREQ_PAUSE\fP) then the response handler will
process any pending RTP data before marking the request as finished.  (Added
in 7.20.0)
.IP CURLOPT_INTERLEAVEDATA
This is the userdata pointer that will be passed to
\fICURLOPT_INTERLEAVEFUNCTION\fP when interleaved RTP data is received. (Added
in 7.20.0)
.IP CURLOPT_CHUNK_BGN_FUNCTION
Pass a pointer to a function that matches the following prototype:
\fBlong function (const void *transfer_info, void *ptr, int remains)\fP. This
function gets called by libcurl before a part of the stream is going to be
transferred (if the transfer supports chunks).

This callback makes sense only when using the \fICURLOPT_WILDCARDMATCH\fP
option for now.

The target of transfer_info parameter is a "feature depended" structure. For
the FTP wildcard download, the target is curl_fileinfo structure (see
\fIcurl/curl.h\fP).  The parameter ptr is a pointer given by
\fICURLOPT_CHUNK_DATA\fP. The parameter remains contains number of chunks
remaining per the transfer. If the feature is not available, the parameter has
zero value.

Return \fICURL_CHUNK_BGN_FUNC_OK\fP if everything is fine,
\fICURL_CHUNK_BGN_FUNC_SKIP\fP if you want to skip the concrete chunk or
\fICURL_CHUNK_BGN_FUNC_FAIL\fP to tell libcurl to stop if some error occurred.
(This was added in 7.21.0)
.IP CURLOPT_CHUNK_END_FUNCTION
Pass a pointer to a function that matches the following prototype:
\fBlong function(void *ptr)\fP. This function gets called by libcurl as soon
as a part of the stream has been transferred (or skipped).

Return \fICURL_CHUNK_END_FUNC_OK\fP if everything is fine or
\fBCURL_CHUNK_END_FUNC_FAIL\fP to tell the lib to stop if some error occurred.
(This was added in 7.21.0)
.IP CURLOPT_CHUNK_DATA
Pass a pointer that will be untouched by libcurl and passed as the ptr
argument to the \fICURL_CHUNK_BGN_FUNTION\fP and \fICURL_CHUNK_END_FUNTION\fP.
(This was added in 7.21.0)
.IP CURLOPT_FNMATCH_FUNCTION
Pass a pointer to a function that matches the following prototype: \fBint
function(void *ptr, const char *pattern, const char *string)\fP prototype (see
\fIcurl/curl.h\fP). It is used internally for the wildcard matching feature.

Return \fICURL_FNMATCHFUNC_MATCH\fP if pattern matches the string,
\fICURL_FNMATCHFUNC_NOMATCH\fP if not or \fICURL_FNMATCHFUNC_FAIL\fP if an
error occurred.  (This was added in 7.21.0)
.IP CURLOPT_FNMATCH_DATA
Pass a pointer that will be untouched by libcurl and passed as the ptr argument
to the \fICURL_FNMATCH_FUNCTION\fP. (This was added in 7.21.0)
.SH ERROR OPTIONS
.IP CURLOPT_ERRORBUFFER
Pass a char * to a buffer that the libcurl may store human readable error
messages in. This may be more helpful than just the return code from
\fIcurl_easy_perform\fP. The buffer must be at least CURL_ERROR_SIZE big.
Although this argument is a 'char *', it does not describe an input string.
Therefore the (probably undefined) contents of the buffer is NOT copied by the
library. You must keep the associated storage available until libcurl no
longer needs it. Failing to do so will cause very odd behavior or even
crashes. libcurl will need it until you call \fIcurl_easy_cleanup(3)\fP or you
set the same option again to use a different pointer.

Use \fICURLOPT_VERBOSE\fP and \fICURLOPT_DEBUGFUNCTION\fP to better
debug/trace why errors happen.

If the library does not return an error, the buffer may not have been
touched. Do not rely on the contents in those cases.

.IP CURLOPT_STDERR
Pass a FILE * as parameter. Tell libcurl to use this stream instead of stderr
when showing the progress meter and displaying \fICURLOPT_VERBOSE\fP data.
.IP CURLOPT_FAILONERROR
A parameter set to 1 tells the library to fail silently if the HTTP code
returned is equal to or larger than 400. The default action would be to return
the page normally, ignoring that code.

This method is not fail-safe and there are occasions where non-successful
response codes will slip through, especially when authentication is involved
(response codes 401 and 407).

You might get some amounts of headers transferred before this situation is
detected, like when a "100-continue" is received as a response to a
POST/PUT and a 401 or 407 is received immediately afterwards.
.SH NETWORK OPTIONS
.IP CURLOPT_URL
Pass in a pointer to the actual URL to deal with. The parameter should be a
char * to a zero terminated string which must be URL-encoded in the following
format:

scheme://host:port/path

For a greater explanation of the format please see RFC3986.

If the given URL lacks the scheme (such as "http://" or "ftp://" etc) then
libcurl will attempt to resolve the protocol based on one of the following
given host names:

HTTP, FTP, DICT, LDAP, IMAP, POP3 or SMTP

(POP3 and SMTP added in 7.31.0)

Should the protocol, either that specified by the scheme or deduced by libcurl
from the host name, not be supported by libcurl then
(\fICURLE_UNSUPPORTED_PROTOCOL\fP) will be returned from either the
\fIcurl_easy_perform(3)\fP or \fIcurl_multi_perform(3)\fP functions when you
call them. Use \fIcurl_version_info(3)\fP for detailed information of which
protocols are supported by the build of libcurl you are using.

The host part of the URL contains the address of the server that you want to
connect to. This can be the fully qualified domain name of the server, the
local network name of the machine on your network or the IP address of the
server or machine represented by either an IPv4 or IPv6 address. For example:

http://www.example.com/

http://hostname/

http://192.168.0.1/

http://[2001:1890:1112:1::20]/

It is also possible to specify the user name, password and any supported login
options as part of the host, for the following protocols, when connecting to
servers that require authentication:

http://user:password@www.example.com

ftp://user:password@ftp.example.com

imap://user:password;options@mail.example.com

pop3://user:password;options@mail.example.com

smtp://user:password;options@mail.example.com

At present only IMAP, POP3 and SMTP support login options as part of the host.
For more information about the login options in URL syntax please see RFC2384,
RFC5092 and IETF draft draft-earhart-url-smtp-00.txt (Added in 7.31.0).

The port is optional and when not specified libcurl will use the default port
based on the determined or specified protocol: 80 for HTTP, 21 for FTP and 25
for SMTP, etc. The following examples show how to specify the port:

http://www.example.com:8080/ - This will connect to a web server using port
8080 rather than 80.

smtp://mail.example.com:587/ - This will connect to a SMTP server on the
alternative mail port.

The path part of the URL is protocol specific and whilst some examples are
given below this list is not conclusive:

.B HTTP

The path part of a HTTP request specifies the file to retrieve and from what
directory. If the directory is not specified then the web server's root
directory is used. If the file is omitted then the default document will be
retrieved for either the directory specified or the root directory. The
exact resource returned for each URL is entirely dependent on the server's
configuration.

http://www.example.com - This gets the main page from the web server.

http://www.example.com/index.html - This returns the main page by explicitly
requesting it.

http://www.example.com/contactus/ - This returns the default document from
the contactus directory.

.B FTP

The path part of an FTP request specifies the file to retrieve and from what
directory. If the file part is omitted then libcurl downloads the directory
listing for the directory specified. If the directory is omitted then
the directory listing for the root / home directory will be returned.

ftp://ftp.example.com - This retrieves the directory listing for the root
directory.

ftp://ftp.example.com/readme.txt - This downloads the file readme.txt from the
root directory.

ftp://ftp.example.com/libcurl/readme.txt - This downloads readme.txt from the
libcurl directory.

ftp://user:password@ftp.example.com/readme.txt - This retrieves the readme.txt
file from the user's home directory. When a username and password is
specified, everything that is specified in the path part is relative to the
user's home directory. To retrieve files from the root directory or a
directory underneath the root directory then the absolute path must be
specified by prepending an additional forward slash to the beginning of the
path.

ftp://user:password@ftp.example.com//readme.txt - This retrieves the readme.txt
from the root directory when logging in as a specified user.

.B SMTP

The path part of a SMTP request specifies the host name to present during
communication with the mail server. If the path is omitted then libcurl will
attempt to resolve the local computer's host name. However, this may not
return the fully qualified domain name that is required by some mail servers
and specifying this path allows you to set an alternative name, such as
your machine's fully qualified domain name, which you might have obtained
from an external function such as gethostname or getaddrinfo.

smtp://mail.example.com - This connects to the mail server at example.com and
sends your local computer's host name in the HELO / EHLO command.

smtp://mail.example.com/client.example.com - This will send client.example.com in
the HELO / EHLO command to the mail server at example.com.

.B POP3

The path part of a POP3 request specifies the message ID to retrieve. If the
ID is not specified then a list of waiting messages is returned instead.

pop3://user:password@mail.example.com - This lists the available messages for
the user

pop3://user:password@mail.example.com/1 - This retrieves the first message for
the user

.B IMAP

The path part of an IMAP request not only specifies the mailbox to list (Added
in 7.30.0) or select, but can also be used to check the UIDVALIDITY of the
mailbox, to specify the UID, SECTION (Added in 7.30.0) and PARTIAL octets
(Added in 7.37.0) of the message to fetch and to specify what nessages to
search for (Added in 7.37.0).

imap://user:password@mail.example.com - Performs a top level folder list

imap://user:password@mail.example.com/INBOX - Performs a folder list on the
user's inbox

imap://user:password@mail.example.com/INBOX/;UID=1 - Selects the user's inbox
and fetches message 1

imap://user:password@mail.example.com/INBOX;UIDVALIDITY=50/;UID=2 - Selects
the user's inbox, checks the UIDVALIDITY of the mailbox is 50 and fetches
message 2 if it is

imap://user:password@mail.example.com/INBOX/;UID=3/;SECTION=TEXT - Selects the
user's inbox and fetches the text portial of message 3

imap://user:password@mail.example.com/INBOX/;UID=4/;PARTIAL=0.1024 - Selects
the user's inbox and fetches the first 1024 octets of message 4

imap://user:password@mail.example.com/INBOX?NEW - Selects the user's inbox and
checks for NEW messages

imap://user:password@mail.example.com/INBOX?SUBJECT%20shadows - Selects the
user's inbox and searches for messages containing "shadows" in the subject
line

For more information about the individual components of an IMAP URL please
see RFC5092.

.B SCP

The path part of a SCP request specifies the file to retrieve and from what
directory. The file part may not be omitted. The file is taken as an absolute
path from the root directory on the server. To specify a path relative to
the user's home directory on the server, prepend ~/ to the path portion.
If the user name is not embedded in the URL, it can be set with the
\fICURLOPT_USERPWD\fP or \fBCURLOPT_USERNAME\fP option.

scp://user@example.com/etc/issue - This specifies the file /etc/issue

scp://example.com/~/my-file - This specifies the file my-file in the
user's home directory on the server

.B SFTP

The path part of a SFTP request specifies the file to retrieve and from what
directory. If the file part is omitted then libcurl downloads the directory
listing for the directory specified.  If the path ends in a / then a directory
listing is returned instead of a file.  If the path is omitted entirely then
the directory listing for the root / home directory will be returned.
If the user name is not embedded in the URL, it can be set with the
\fICURLOPT_USERPWD\fP or \fBCURLOPT_USERNAME\fP option.

sftp://user:password@example.com/etc/issue - This specifies the file
/etc/issue

sftp://user@example.com/~/my-file - This specifies the file my-file in the
user's home directory

sftp://ssh.example.com/~/Documents/ - This requests a directory listing
of the Documents directory under the user's home directory

.B LDAP

The path part of a LDAP request can be used to specify the: Distinguished
Name, Attributes, Scope, Filter and Extension for a LDAP search. Each field
is separated by a question mark and when that field is not required an empty
string with the question mark separator should be included.

ldap://ldap.example.com/o=My%20Organisation - This will perform a LDAP search
with the DN as My Organisation.

ldap://ldap.example.com/o=My%20Organisation?postalAddress - This will perform
the same search but will only return postalAddress attributes.

ldap://ldap.example.com/?rootDomainNamingContext - This specifies an empty DN
and requests information about the rootDomainNamingContext attribute for an
Active Directory server.

For more information about the individual components of a LDAP URL please
see RFC4516.

.B RTMP

There's no official URL spec for RTMP so libcurl uses the URL syntax supported
by the underlying librtmp library. It has a syntax where it wants a
traditional URL, followed by a space and a series of space-separated
name=value pairs.

While space is not typically a "legal" letter, libcurl accepts them. When a
user wants to pass in a '#' (hash) character it will be treated as a fragment
and get cut off by libcurl if provided literally. You will instead have to
escape it by providing it as backslash and its ASCII value in hexadecimal:
"\\23".

.B NOTES

Starting with version 7.20.0, the fragment part of the URI will not be sent as
part of the path, which was previously the case.

\fICURLOPT_URL\fP is the only option that \fBmust\fP be set before
\fIcurl_easy_perform(3)\fP is called.

\fICURLOPT_PROTOCOLS\fP can be used to limit what protocols libcurl will use
for this transfer, independent of what libcurl has been compiled to
support. That may be useful if you accept the URL from an external source and
want to limit the accessibility.
.IP CURLOPT_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If used, this bitmask
limits what protocols libcurl may use in the transfer. This allows you to have
a libcurl built to support a wide range of protocols but still limit specific
transfers to only be allowed to use a subset of them. By default libcurl will
accept all protocols it supports. See also
\fICURLOPT_REDIR_PROTOCOLS\fP. (Added in 7.19.4)
.IP CURLOPT_REDIR_PROTOCOLS
Pass a long that holds a bitmask of CURLPROTO_* defines. If used, this bitmask
limits what protocols libcurl may use in a transfer that it follows to in a
redirect when \fICURLOPT_FOLLOWLOCATION\fP is enabled. This allows you to
limit specific transfers to only be allowed to use a subset of protocols in
redirections. By default libcurl will allow all protocols except for FILE and
SCP. This is a difference compared to pre-7.19.4 versions which
unconditionally would follow to all protocols supported. (Added in 7.19.4)
.IP CURLOPT_PROXY
Set HTTP proxy to use. The parameter should be a char * to a zero terminated
string holding the host name or dotted IP address. To specify port number in
this string, append :[port] to the end of the host name. The proxy string may
be prefixed with [protocol]:// since any such prefix will be ignored. The
proxy's port number may optionally be specified with the separate option
\fICURLOPT_PROXYPORT\fP. If not specified, libcurl will default to using port
1080 for proxies.

When you tell the library to use a HTTP proxy, libcurl will transparently
convert operations to HTTP even if you specify an FTP URL etc. This may have
an impact on what other features of the library you can use, such as
\fICURLOPT_QUOTE\fP and similar FTP specifics that don't work unless you
tunnel through the HTTP proxy. Such tunneling is activated with
\fICURLOPT_HTTPPROXYTUNNEL\fP.

libcurl respects the environment variables \fBhttp_proxy\fP, \fBftp_proxy\fP,
\fBall_proxy\fP etc, if any of those are set. The \fICURLOPT_PROXY\fP option
does however override any possibly set environment variables.

Setting the proxy string to "" (an empty string) will explicitly disable the
use of a proxy, even if there is an environment variable set for it.

Since 7.14.1, the proxy host string given in environment variables can be
specified the exact same way as the proxy can be set with \fICURLOPT_PROXY\fP,
include protocol prefix (http://) and embedded user + password.

Since 7.21.7, the proxy string may be specified with a protocol:// prefix to
specify alternative proxy protocols. Use socks4://, socks4a://, socks5:// or
socks5h:// (the last one to enable socks5 and asking the proxy to do the
resolving, also known as CURLPROXY_SOCKS5_HOSTNAME type) to request the
specific SOCKS version to be used. No protocol specified, http:// and all
others will be treated as HTTP proxies.
.IP CURLOPT_PROXYPORT
Pass a long with this option to set the proxy port to connect to unless it is
specified in the proxy string \fICURLOPT_PROXY\fP.
.IP CURLOPT_PROXYTYPE
Pass a long with this option to set type of the proxy. Available options for
this are \fICURLPROXY_HTTP\fP, \fICURLPROXY_HTTP_1_0\fP (added in 7.19.4),
\fICURLPROXY_SOCKS4\fP (added in 7.10), \fICURLPROXY_SOCKS5\fP,
\fICURLPROXY_SOCKS4A\fP (added in 7.18.0) and \fICURLPROXY_SOCKS5_HOSTNAME\fP
(added in 7.18.0). The HTTP type is default. (Added in 7.10)

If you set \fBCURLOPT_PROXYTYPE\fP to \fICURLPROXY_HTTP_1_0\fP, it will only
affect how libcurl speaks to a proxy when CONNECT is used. The HTTP version
used for "regular" HTTP requests is instead controlled with
\fICURLOPT_HTTP_VERSION\fP.
.IP CURLOPT_NOPROXY
Pass a pointer to a zero terminated string. The string consists of a comma
separated list of host names that do not require a proxy to get reached, even
if one is specified.  The only wildcard available is a single * character,
which matches all hosts, and effectively disables the proxy. Each name in this
list is matched as either a domain which contains the hostname, or the
hostname itself. For example, example.com would match example.com,
example.com:80, and www.example.com, but not www.notanexample.com or
example.com.othertld.  (Added in 7.19.4)
.IP CURLOPT_HTTPPROXYTUNNEL
Set the parameter to 1 to make the library tunnel all operations through a
given HTTP proxy. There is a big difference between using a proxy and to
tunnel through it. If you don't know what this means, you probably don't want
this tunneling option.
.IP CURLOPT_SOCKS5_GSSAPI_SERVICE
Pass a char * as parameter to a string holding the name of the service. The
default service name for a SOCKS5 server is rcmd/server-fqdn. This option
allows you to change it. (Added in 7.19.4)
.IP CURLOPT_SOCKS5_GSSAPI_NEC
Pass a long set to 1 to enable or 0 to disable. As part of the gssapi
negotiation a protection mode is negotiated. The RFC1961 says in section
4.3/4.4 it should be protected, but the NEC reference implementation does not.
If enabled, this option allows the unprotected exchange of the protection mode
negotiation. (Added in 7.19.4).
.IP CURLOPT_INTERFACE
Pass a char * as parameter. This sets the interface name to use as outgoing
network interface. The name can be an interface name, an IP address, or a host
name.

Starting with 7.24.0: If the parameter starts with "if!" then it is treated as
only as interface name and no attempt will ever be named to do treat it as an
IP address or to do name resolution on it.  If the parameter starts with
\&"host!" it is treated as either an IP address or a hostname.  Hostnames are
resolved synchronously.  Using the if! format is highly recommended when using
the multi interfaces to avoid allowing the code to block.  If "if!" is
specified but the parameter does not match an existing interface,
CURLE_INTERFACE_FAILED is returned.
.IP CURLOPT_LOCALPORT
Pass a long. This sets the local port number of the socket used for
connection. This can be used in combination with \fICURLOPT_INTERFACE\fP and
you are recommended to use \fICURLOPT_LOCALPORTRANGE\fP as well when this is
set. Valid port numbers are 1 - 65535. (Added in 7.15.2)
.IP CURLOPT_LOCALPORTRANGE
Pass a long. This is the number of attempts libcurl will make to find a
working local port number. It starts with the given \fICURLOPT_LOCALPORT\fP
and adds one to the number for each retry. Setting this to 1 or below will
make libcurl do only one try for the exact port number. Port numbers by nature
are scarce resources that will be busy at times so setting this value to
something too low might cause unnecessary connection setup failures. (Added in
7.15.2)
.IP CURLOPT_DNS_CACHE_TIMEOUT
Pass a long, this sets the timeout in seconds. Name resolves will be kept in
memory for this number of seconds. Set to zero to completely disable
caching, or set to -1 to make the cached entries remain forever. By default,
libcurl caches this info for 60 seconds.

The name resolve functions of various libc implementations don't re-read name
server information unless explicitly told so (for example, by calling
\fIres_init(3)\fP). This may cause libcurl to keep using the older server even
if DHCP has updated the server info, and this may look like a DNS cache issue
to the casual libcurl-app user.
.IP CURLOPT_DNS_USE_GLOBAL_CACHE
Pass a long. If the value is 1, it tells curl to use a global DNS cache
that will survive between easy handle creations and deletions. This is not
thread-safe and this will use a global variable.

\fBWARNING:\fP this option is considered obsolete. Stop using it. Switch over
to using the share interface instead! See \fICURLOPT_SHARE\fP and
\fIcurl_share_init(3)\fP.
.IP CURLOPT_BUFFERSIZE
Pass a long specifying your preferred size (in bytes) for the receive buffer
in libcurl.  The main point of this would be that the write callback gets
called more often and with smaller chunks. This is just treated as a request,
not an order. You cannot be guaranteed to actually get the given size. (Added
in 7.10)

This size is by default set as big as possible (CURL_MAX_WRITE_SIZE), so it
only makes sense to use this option if you want it smaller.
.IP CURLOPT_PORT
Pass a long specifying what remote port number to connect to, instead of the
one specified in the URL or the default port for the used protocol.
.IP CURLOPT_TCP_NODELAY
Pass a long specifying whether the TCP_NODELAY option is to be set or cleared
(1 = set, 0 = clear). The option is cleared by default. This will have no
effect after the connection has been established.

Setting this option will disable TCP's Nagle algorithm. The purpose of this
algorithm is to try to minimize the number of small packets on the network
(where "small packets" means TCP segments less than the Maximum Segment Size
(MSS) for the network).

Maximizing the amount of data sent per TCP segment is good because it
amortizes the overhead of the send. However, in some cases (most notably
telnet or rlogin) small segments may need to be sent without delay. This is
less efficient than sending larger amounts of data at a time, and can
contribute to congestion on the network if overdone.
.IP CURLOPT_ADDRESS_SCOPE
Pass a long specifying the scope_id value to use when connecting to IPv6
link-local or site-local addresses. (Added in 7.19.0)
.IP CURLOPT_TCP_KEEPALIVE
Pass a long. If set to 1, TCP keepalive probes will be sent. The delay and
frequency of these probes can be controlled by the \fICURLOPT_TCP_KEEPIDLE\fP
and \fICURLOPT_TCP_KEEPINTVL\fP options, provided the operating system supports
them. Set to 0 (default behavior) to disable keepalive probes (Added in
7.25.0).
.IP CURLOPT_TCP_KEEPIDLE
Pass a long. Sets the delay, in seconds, that the operating system will wait
while the connection is idle before sending keepalive probes. Not all operating
systems support this option. (Added in 7.25.0)
.IP CURLOPT_TCP_KEEPINTVL
Pass a long. Sets the interval, in seconds, that the operating system will wait
between sending keepalive probes. Not all operating systems support this
option. (Added in 7.25.0)
.SH NAMES and PASSWORDS OPTIONS (Authentication)
.IP CURLOPT_NETRC
This parameter controls the preference of libcurl between using user names and
passwords from your \fI~/.netrc\fP file, relative to user names and passwords
in the URL supplied with \fICURLOPT_URL\fP.

libcurl uses a user name (and supplied or prompted password) supplied with
\fICURLOPT_USERPWD\fP in preference to any of the options controlled by this
parameter.

Pass a long, set to one of the values described below.
.RS
.IP CURL_NETRC_OPTIONAL
The use of your \fI~/.netrc\fP file is optional, and information in the URL is
to be preferred.  The file will be scanned for the host and user name (to
find the password only) or for the host only, to find the first user name and
password after that \fImachine\fP, which ever information is not specified in
the URL.

Undefined values of the option will have this effect.
.IP CURL_NETRC_IGNORED
The library will ignore the file and use only the information in the URL.

This is the default.
.IP CURL_NETRC_REQUIRED
This value tells the library that use of the file is required, to ignore the
information in the URL, and to search the file for the host only.
.RE
Only machine name, user name and password are taken into account
(init macros and similar things aren't supported).

libcurl does not verify that the file has the correct properties set (as the
standard Unix ftp client does). It should only be readable by user.
.IP CURLOPT_NETRC_FILE
Pass a char * as parameter, pointing to a zero terminated string containing
the full path name to the file you want libcurl to use as .netrc file. If this
option is omitted, and \fICURLOPT_NETRC\fP is set, libcurl will attempt to
find a .netrc file in the current user's home directory. (Added in 7.10.9)
.IP CURLOPT_USERPWD
Pass a char * as parameter, pointing to a zero terminated login details string
for the connection. The format of which is: [user name]:[password].

When using NTLM, you can set the domain by prepending it to the user name and
separating the domain and name with a forward (/) or backward slash (\\). Like
this: "domain/user:password" or "domain\\user:password". Some HTTP servers (on
Windows) support this style even for Basic authentication.

When using HTTP and \fICURLOPT_FOLLOWLOCATION\fP, libcurl might perform
several requests to possibly different hosts. libcurl will only send this user
and password information to hosts using the initial host name (unless
\fICURLOPT_UNRESTRICTED_AUTH\fP is set), so if libcurl follows locations to
other hosts it will not send the user and password to those. This is enforced
to prevent accidental information leakage.

Use \fICURLOPT_HTTPAUTH\fP to specify the authentication method for HTTP based
connections or \fICURLOPT_LOGIN_OPTIONS\fP to control IMAP, POP3 and SMTP
options.

The user and password strings are not URL decoded, so there's no way to send
in a user name containing a colon using this option. Use \fICURLOPT_USERNAME\fP
for that, or include it in the URL.
.IP CURLOPT_PROXYUSERPWD
Pass a char * as parameter, which should be [user name]:[password] to use for
the connection to the HTTP proxy. Both the name and the password will be URL
decoded before use, so to include for example a colon in the user name you
should encode it as %3A.

Use \fICURLOPT_PROXYAUTH\fP to specify the authentication method.
.IP CURLOPT_USERNAME
Pass a char * as parameter, which should be pointing to the zero terminated
user name to use for the transfer.

\fBCURLOPT_USERNAME\fP sets the user name to be used in protocol
authentication. You should not use this option together with the (older)
CURLOPT_USERPWD option.

To specify the password and login options, along with the user name, use the
\fICURLOPT_PASSWORD\fP and \fICURLOPT_LOGIN_OPTIONS\fP options. (Added in
7.19.1)
.IP CURLOPT_PASSWORD
Pass a char * as parameter, which should be pointing to the zero terminated
password to use for the transfer.

The CURLOPT_PASSWORD option should be used in conjunction with the
\fICURLOPT_USERNAME\fP option. (Added in 7.19.1)
.IP CURLOPT_LOGIN_OPTIONS
(Added in 7.34.0) Pass a char * as parameter, which should be pointing to the
zero terminated options string to use for the transfer.

At present only IMAP, POP3 and SMTP support login options. For more
information about the login options please see RFC2384, RFC5092 and IETF draft
draft-earhart-url-smtp-00.txt

\fBCURLOPT_LOGIN_OPTIONS\fP can be used to set protocol specific login options,
such as the preferred authentication mechanism via "AUTH=NTLM" or "AUTH=*",
and should be used in conjunction with the \fICURLOPT_USERNAME\fP option.
.IP CURLOPT_PROXYUSERNAME
Pass a char * as parameter, which should be pointing to the zero terminated
user name to use for the transfer while connecting to Proxy.

The CURLOPT_PROXYUSERNAME option should be used in same way as the
\fICURLOPT_PROXYUSERPWD\fP is used.  In comparison to
\fICURLOPT_PROXYUSERPWD\fP the CURLOPT_PROXYUSERNAME allows the username to
contain a colon, like in the following example: "sip:user@example.com". The
CURLOPT_PROXYUSERNAME option is an alternative way to set the user name while
connecting to Proxy.  There is no meaning to use it together with the
\fICURLOPT_PROXYUSERPWD\fP option.

In order to specify the password to be used in conjunction with the user name
use the \fICURLOPT_PROXYPASSWORD\fP option.  (Added in 7.19.1)
.IP CURLOPT_PROXYPASSWORD
Pass a char * as parameter, which should be pointing to the zero terminated
password to use for the transfer while connecting to Proxy.

The CURLOPT_PROXYPASSWORD option should be used in conjunction with
the \fICURLOPT_PROXYUSERNAME\fP option. (Added in 7.19.1)
.IP CURLOPT_HTTPAUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl which
authentication method(s) you want it to use. The available bits are listed
below. If more than one bit is set, libcurl will first query the site to see
which authentication methods it supports and then pick the best one you allow
it to use. For some methods, this will induce an extra network round-trip. Set
the actual name and password with the \fICURLOPT_USERPWD\fP option or
with the \fICURLOPT_USERNAME\fP and the \fICURLOPT_PASSWORD\fP options.
(Added in 7.10.6)
.RS
.IP CURLAUTH_BASIC
HTTP Basic authentication. This is the default choice, and the only method
that is in wide-spread use and supported virtually everywhere. This sends
the user name and password over the network in plain text, easily captured by
others.
.IP CURLAUTH_DIGEST
HTTP Digest authentication.  Digest authentication is defined in RFC2617 and
is a more secure way to do authentication over public networks than the
regular old-fashioned Basic method.
.IP CURLAUTH_DIGEST_IE
HTTP Digest authentication with an IE flavor.  Digest authentication is
defined in RFC2617 and is a more secure way to do authentication over public
networks than the regular old-fashioned Basic method. The IE flavor is simply
that libcurl will use a special "quirk" that IE is known to have used before
version 7 and that some servers require the client to use. (This define was
added in 7.19.3)
.IP CURLAUTH_GSSNEGOTIATE
HTTP GSS-Negotiate authentication. The GSS-Negotiate (also known as plain
\&"Negotiate") method was designed by Microsoft and is used in their web
applications. It is primarily meant as a support for Kerberos5 authentication
but may also be used along with other authentication methods. For more
information see IETF draft draft-brezak-spnego-http-04.txt.

You need to build libcurl with a suitable GSS-API library for this to work.
.IP CURLAUTH_NTLM
HTTP NTLM authentication. A proprietary protocol invented and used by
Microsoft. It uses a challenge-response and hash concept similar to Digest, to
prevent the password from being eavesdropped.

You need to build libcurl with either OpenSSL, GnuTLS or NSS support for this
option to work, or build libcurl on Windows with SSPI support.
.IP CURLAUTH_NTLM_WB
NTLM delegating to winbind helper. Authentication is performed by a separate
binary application that is executed when needed. The name of the application
is specified at compile time but is typically /usr/bin/ntlm_auth
(Added in 7.22.0)

Note that libcurl will fork when necessary to run the winbind application and
kill it when complete, calling waitpid() to await its exit when done. On POSIX
operating systems, killing the process will cause a SIGCHLD signal to be
raised (regardless of whether \fICURLOPT_NOSIGNAL\fP is set), which must be
handled intelligently by the application. In particular, the application must
not unconditionally call wait() in its SIGCHLD signal handler to avoid being
subject to a race condition.  This behavior is subject to change in future
versions of libcurl.
.IP CURLAUTH_ANY
This is a convenience macro that sets all bits and thus makes libcurl pick any
it finds suitable. libcurl will automatically select the one it finds most
secure.
.IP CURLAUTH_ANYSAFE
This is a convenience macro that sets all bits except Basic and thus makes
libcurl pick any it finds suitable. libcurl will automatically select the one
it finds most secure.
.IP CURLAUTH_ONLY
This is a meta symbol. Or this value together with a single specific auth
value to force libcurl to probe for un-restricted auth and if not, only that
single auth algorithm is acceptable. (Added in 7.21.3)
.RE
.IP CURLOPT_TLSAUTH_TYPE
Pass a long as parameter, which is set to a bitmask, to tell libcurl which
authentication method(s) you want it to use for TLS authentication.
.RS
.IP CURLOPT_TLSAUTH_SRP
TLS-SRP authentication. Secure Remote Password authentication for TLS is
defined in RFC5054 and provides mutual authentication if both sides have a
shared secret. To use TLS-SRP, you must also set the
\fICURLOPT_TLSAUTH_USERNAME\fP and \fICURLOPT_TLSAUTH_PASSWORD\fP options.

You need to build libcurl with GnuTLS or OpenSSL with TLS-SRP support for this
to work. (Added in 7.21.4)
.RE
.IP CURLOPT_TLSAUTH_USERNAME
Pass a char * as parameter, which should point to the zero terminated username
to use for the TLS authentication method specified with the
\fICURLOPT_TLSAUTH_TYPE\fP option. Requires that the
\fICURLOPT_TLS_PASSWORD\fP option also be set. (Added in 7.21.4)
.IP CURLOPT_TLSAUTH_PASSWORD
Pass a char * as parameter, which should point to the zero terminated password
to use for the TLS authentication method specified with the
\fICURLOPT_TLSAUTH_TYPE\fP option. Requires that the
\fICURLOPT_TLS_USERNAME\fP option also be set. (Added in 7.21.4)
.IP CURLOPT_PROXYAUTH
Pass a long as parameter, which is set to a bitmask, to tell libcurl which
authentication method(s) you want it to use for your proxy authentication.  If
more than one bit is set, libcurl will first query the site to see what
authentication methods it supports and then pick the best one you allow it to
use. For some methods, this will induce an extra network round-trip. Set the
actual name and password with the \fICURLOPT_PROXYUSERPWD\fP option. The
bitmask can be constructed by or'ing together the bits listed above for the
\fICURLOPT_HTTPAUTH\fP option. \fICURLOPT_PROXYAUTH\fP was added in 7.10.7
.IP CURLOPT_SASL_IR
Pass a long. If the value is 1, curl will send the initial response to the
server in the first authentication packet in order to reduce the number of
ping pong requests. Only applicable to supporting SASL authentication
mechanisms and to the IMAP, POP3 and SMTP protocols. (Added in 7.31.0)

Note: Whilst IMAP supports this option there is no need to explicitly set it,
as libcurl can determine the feature itself when the server supports the
SASL-IR CAPABILITY.
.IP CURLOPT_XOAUTH2_BEARER
Pass a char * as parameter, which should point to the zero terminated OAuth
2.0 Bearer Access Token for use with IMAP, POP3 and SMTP servers that support
the OAuth 2.0 Authorization Framework. (Added in 7.33.0)

Note: The user name used to generate the Bearer Token should be supplied via
the \fICURLOPT_USERNAME\fP option.
.SH HTTP OPTIONS
.IP CURLOPT_AUTOREFERER
Pass a parameter set to 1 to enable this. When enabled, libcurl will
automatically set the Referer: field in requests where it follows a Location:
redirect.
.IP CURLOPT_ACCEPT_ENCODING
Sets the contents of the Accept-Encoding: header sent in a HTTP request, and
enables decoding of a response when a Content-Encoding: header is received.
Three encodings are supported: \fIidentity\fP, which does nothing,
\fIdeflate\fP which requests the server to compress its response using the
zlib algorithm, and \fIgzip\fP which requests the gzip algorithm.  If a
zero-length string is set, then an Accept-Encoding: header containing all
supported encodings is sent.

This is a request, not an order; the server may or may not do it.  This option
must be set (to any non-NULL value) or else any unsolicited encoding done by
the server is ignored. See the special file lib/README.encoding for details.

(This option was called CURLOPT_ENCODING before 7.21.6)
.IP CURLOPT_TRANSFER_ENCODING
Adds a request for compressed Transfer Encoding in the outgoing HTTP
request. If the server supports this and so desires, it can respond with the
HTTP response sent using a compressed Transfer-Encoding that will be
automatically uncompressed by libcurl on reception.

Transfer-Encoding differs slightly from the Content-Encoding you ask for with
\fBCURLOPT_ACCEPT_ENCODING\fP in that a Transfer-Encoding is strictly meant to
be for the transfer and thus MUST be decoded before the data arrives in the
client. Traditionally, Transfer-Encoding has been much less used and supported
by both HTTP clients and HTTP servers.

(Added in 7.21.6)
.IP CURLOPT_FOLLOWLOCATION
A parameter set to 1 tells the library to follow any Location: header that the
server sends as part of a HTTP header.

This means that the library will re-send the same request on the new location
and follow new Location: headers all the way until no more such headers are
returned. \fICURLOPT_MAXREDIRS\fP can be used to limit the number of redirects
libcurl will follow.

Since 7.19.4, libcurl can limit what protocols it will automatically
follow. The accepted protocols are set with \fICURLOPT_REDIR_PROTOCOLS\fP and
it excludes the FILE protocol by default.
.IP CURLOPT_UNRESTRICTED_AUTH
A parameter set to 1 tells the library it can continue to send authentication
(user+password) when following locations, even when hostname changed. This
option is meaningful only when setting \fICURLOPT_FOLLOWLOCATION\fP.
.IP CURLOPT_MAXREDIRS
Pass a long. The set number will be the redirection limit. If that many
redirections have been followed, the next redirect will cause an error
(\fICURLE_TOO_MANY_REDIRECTS\fP). This option only makes sense if the
\fICURLOPT_FOLLOWLOCATION\fP is used at the same time. Added in 7.15.1:
Setting the limit to 0 will make libcurl refuse any redirect. Set it to -1 for
an infinite number of redirects (which is the default)
.IP CURLOPT_POSTREDIR
Pass a bitmask to control how libcurl acts on redirects after POSTs that get a
301, 302 or 303 response back.  A parameter with bit 0 set (value
\fBCURL_REDIR_POST_301\fP) tells the library to respect RFC2616/10.3.2 and not
convert POST requests into GET requests when following a 301 redirection.
Setting bit 1 (value \fBCURL_REDIR_POST_302\fP) makes libcurl maintain the
request method after a 302 redirect whilst setting bit 2 (value
\fBCURL_REDIR_POST_303\fP) makes libcurl maintain the request method after a
303 redirect. The value \fBCURL_REDIR_POST_ALL\fP is a convenience define that
sets all three bits.

The non-RFC behaviour is ubiquitous in web browsers, so the library does the
conversion by default to maintain consistency. However, a server may require a
POST to remain a POST after such a redirection. This option is meaningful only
when setting \fICURLOPT_FOLLOWLOCATION\fP.  (Added in 7.17.1) (This option was
known as CURLOPT_POST301 up to 7.19.0 as it only supported the 301 then)
.IP CURLOPT_PUT
A parameter set to 1 tells the library to use HTTP PUT to transfer data. The
data should be set with \fICURLOPT_READDATA\fP and \fICURLOPT_INFILESIZE\fP.

This option is deprecated and starting with version 7.12.1 you should instead
use \fICURLOPT_UPLOAD\fP.
.IP CURLOPT_POST
A parameter set to 1 tells the library to do a regular HTTP post. This will
also make the library use a "Content-Type:
application/x-www-form-urlencoded" header. (This is by far the most commonly
used POST method).

Use one of \fICURLOPT_POSTFIELDS\fP or \fICURLOPT_COPYPOSTFIELDS\fP options to
specify what data to post and \fICURLOPT_POSTFIELDSIZE\fP or
\fICURLOPT_POSTFIELDSIZE_LARGE\fP to set the data size.

Optionally, you can provide data to POST using the \fICURLOPT_READFUNCTION\fP
and \fICURLOPT_READDATA\fP options but then you must make sure to not set
\fICURLOPT_POSTFIELDS\fP to anything but NULL. When providing data with a
callback, you must transmit it using chunked transfer-encoding or you must set
the size of the data with the \fICURLOPT_POSTFIELDSIZE\fP or
\fICURLOPT_POSTFIELDSIZE_LARGE\fP option. To enable chunked encoding, you
simply pass in the appropriate Transfer-Encoding header, see the
post-callback.c example.

You can override the default POST Content-Type: header by setting your own
with \fICURLOPT_HTTPHEADER\fP.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

If you use POST to a HTTP 1.1 server, you can send data without knowing the
size before starting the POST if you use chunked encoding. You enable this by
adding a header like "Transfer-Encoding: chunked" with
\fICURLOPT_HTTPHEADER\fP. With HTTP 1.0 or without chunked transfer, you must
specify the size in the request.

When setting \fICURLOPT_POST\fP to 1, it will automatically set
\fICURLOPT_NOBODY\fP to 0 (since 7.14.1).

If you issue a POST request and then want to make a HEAD or GET using the same
re-used handle, you must explicitly set the new request type using
\fICURLOPT_NOBODY\fP or \fICURLOPT_HTTPGET\fP or similar.
.IP CURLOPT_POSTFIELDS
Pass a void * as parameter, which should be the full data to post in a HTTP
POST operation. You must make sure that the data is formatted the way you want
the server to receive it. libcurl will not convert or encode it for you. Most
web servers will assume this data to be url-encoded.

The pointed data are NOT copied by the library: as a consequence, they must
be preserved by the calling application until the transfer finishes.

This POST is a normal application/x-www-form-urlencoded kind (and libcurl will
set that Content-Type by default when this option is used), which is the most
commonly used one by HTML forms. See also the \fICURLOPT_POST\fP. Using
\fICURLOPT_POSTFIELDS\fP implies \fICURLOPT_POST\fP.

If you want to do a zero-byte POST, you need to set
\fICURLOPT_POSTFIELDSIZE\fP explicitly to zero, as simply setting
\fICURLOPT_POSTFIELDS\fP to NULL or "" just effectively disables the sending
of the specified string. libcurl will instead assume that you'll send the POST
data using the read callback!

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

To make multipart/formdata posts (aka RFC2388-posts), check out the
\fICURLOPT_HTTPPOST\fP option.
.IP CURLOPT_POSTFIELDSIZE
If you want to post data to the server without letting libcurl do a strlen()
to measure the data size, this option must be used. When this option is used
you can post fully binary data, which otherwise is likely to fail. If this
size is set to -1, the library will use strlen() to get the size.
.IP CURLOPT_POSTFIELDSIZE_LARGE
Pass a curl_off_t as parameter. Use this to set the size of the
\fICURLOPT_POSTFIELDS\fP data to prevent libcurl from doing strlen() on the
data to figure out the size. This is the large file version of the
\fICURLOPT_POSTFIELDSIZE\fP option. (Added in 7.11.1)
.IP CURLOPT_COPYPOSTFIELDS
Pass a char * as parameter, which should be the full data to post in a HTTP
POST operation. It behaves as the \fICURLOPT_POSTFIELDS\fP option, but the
original data are copied by the library, allowing the application to overwrite
the original data after setting this option.

Because data are copied, care must be taken when using this option in
conjunction with \fICURLOPT_POSTFIELDSIZE\fP or
\fICURLOPT_POSTFIELDSIZE_LARGE\fP: If the size has not been set prior to
\fICURLOPT_COPYPOSTFIELDS\fP, the data are assumed to be a NUL-terminated
string; else the stored size informs the library about the data byte count to
copy. In any case, the size must not be changed after
\fICURLOPT_COPYPOSTFIELDS\fP, unless another \fICURLOPT_POSTFIELDS\fP or
\fICURLOPT_COPYPOSTFIELDS\fP option is issued.
(Added in 7.17.1)
.IP CURLOPT_HTTPPOST
Tells libcurl you want a multipart/formdata HTTP POST to be made and you
instruct what data to pass on to the server.  Pass a pointer to a linked list
of curl_httppost structs as parameter.  The easiest way to create such a
list, is to use \fIcurl_formadd(3)\fP as documented. The data in this list
must remain intact until you close this curl handle again with
\fIcurl_easy_cleanup(3)\fP.

Using POST with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

When setting \fICURLOPT_HTTPPOST\fP, it will automatically set
\fICURLOPT_NOBODY\fP to 0 (since 7.14.1).
.IP CURLOPT_REFERER
Pass a pointer to a zero terminated string as parameter. It will be used to
set the Referer: header in the http request sent to the remote server. This
can be used to fool servers or scripts. You can also set any custom header
with \fICURLOPT_HTTPHEADER\fP.
.IP CURLOPT_USERAGENT
Pass a pointer to a zero terminated string as parameter. It will be used to
set the User-Agent: header in the http request sent to the remote server. This
can be used to fool servers or scripts. You can also set any custom header
with \fICURLOPT_HTTPHEADER\fP.
.IP CURLOPT_HTTPHEADER
Pass a pointer to a linked list of HTTP headers to pass to the server and/or
proxy in your HTTP request. The same list is used for both host and proxy
requests!

The linked list should be a fully valid list of \fBstruct curl_slist\fP
structs properly filled in. Use \fIcurl_slist_append(3)\fP to create the list
and \fIcurl_slist_free_all(3)\fP to clean up an entire list. If you add a
header that is otherwise generated and used by libcurl internally, your added
one will be used instead. If you add a header with no content as in 'Accept:'
(no data on the right side of the colon), the internally used header will get
disabled. With this option you can add new headers, replace internal headers
and remove internal headers. To add a header with no content (nothing to the
right side of the colon), use the form 'MyHeader;' (note the ending
semicolon).

The headers included in the linked list must not be CRLF-terminated, because
curl adds CRLF after each header item. Failure to comply with this will result
in strange bugs because the server will most likely ignore part of the headers
you specified.

The first line in a request (containing the method, usually a GET or POST) is
not a header and cannot be replaced using this option. Only the lines
following the request-line are headers. Adding this method line in this list
of headers will only cause your request to send an invalid header.

Pass a NULL to this to reset back to no custom headers.

The most commonly replaced headers have "shortcuts" in the options
\fICURLOPT_COOKIE\fP, \fICURLOPT_USERAGENT\fP and \fICURLOPT_REFERER\fP.

There's an alternative option that sets or replaces headers only for requests
that are sent with CONNECT to a proxy: \fICURLOPT_PROXYHEADER\fP. Use
\fICURLOPT_HEADEROPT\fP to control the behavior.
.IP CURLOPT_HEADEROPT
Pass a long that is a bitmask of options of how to deal with headers. The two
mutually exclusive options are:

CURLHEADER_UNIFIED - keep working as before. This means CURLOPT_HTTPHEADER
headers will be used in requests both to servers and proxies. With this option
enabled, \fICURLOPT_PROXYHEADER\fP will not have any effect.

CURLHEADER_SEPARATE - makes \fICURLOPT_HTTPHEADER\fP headers only get sent to
a server and not to a proxy. Proxy headers must be set with
\fICURLOPT_PROXYHEADER\fP to get used. Note that if a non-CONNECT request is
sent to a proxy, libcurl will send both server headers and proxy headers. When
doing CONNECT, libcurl will send \fICURLOPT_PROXYHEADER\fP headers only do the
proxy and then \fICURLOPT_HTTPHEADER\fP headers only to the server.

(Added in 7.37.0)
.IP CURLOPT_PROXYHEADER
Pass a pointer to a linked list of HTTP headers to pass in your HTTP request
sent to a proxy. The rules for this list is identical to the
\fICURLOPT_HTTPHEADER\fP option's.

The headers set with this option is only ever used in requests sent to a proxy
- when there's also a request sent to a host.

The first line in a request (containing the method, usually a GET or POST) is
NOT a header and cannot be replaced using this option. Only the lines
following the request-line are headers. Adding this method line in this list
of headers will only cause your request to send an invalid header.

Pass a NULL to this to reset back to no custom headers.

This option was added in libcurl 7.37.0.
.IP CURLOPT_HTTP200ALIASES
Pass a pointer to a linked list of aliases to be treated as valid HTTP 200
responses.  Some servers respond with a custom header response line.  For
example, IceCast servers respond with "ICY 200 OK".  By including this string
in your list of aliases, the response will be treated as a valid HTTP header
line such as "HTTP/1.0 200 OK". (Added in 7.10.3)

The linked list should be a fully valid list of struct curl_slist structs, and
be properly filled in.  Use \fIcurl_slist_append(3)\fP to create the list and
\fIcurl_slist_free_all(3)\fP to clean up an entire list.

The alias itself is not parsed for any version strings. Before libcurl 7.16.3,
Libcurl used the value set by option \fICURLOPT_HTTP_VERSION\fP, but starting
with 7.16.3 the protocol is assumed to match HTTP 1.0 when an alias matched.
.IP CURLOPT_COOKIE
Pass a pointer to a zero terminated string as parameter. It will be used to
set a cookie in the http request. The format of the string should be
NAME=CONTENTS, where NAME is the cookie name and CONTENTS is what the cookie
should contain.

If you need to set multiple cookies, you need to set them all using a single
option and thus you need to concatenate them all in one single string. Set
multiple cookies in one string like this: "name1=content1; name2=content2;"
etc.

This option sets the cookie header explicitly in the outgoing request(s). If
multiple requests are done due to authentication, followed redirections or
similar, they will all get this cookie passed on.

Using this option multiple times will only make the latest string override the
previous ones.
.IP CURLOPT_COOKIEFILE
Pass a pointer to a zero terminated string as parameter. It should contain the
name of your file holding cookie data to read. The cookie data may be in
Netscape / Mozilla cookie data format or just regular HTTP-style headers
dumped to a file.

Given an empty or non-existing file or by passing the empty string (""), this
option will enable cookies for this curl handle, making it understand and
parse received cookies and then use matching cookies in future requests.

If you use this option multiple times, you just add more files to read.
Subsequent files will add more cookies.
.IP CURLOPT_COOKIEJAR
Pass a file name as char *, zero terminated. This will make libcurl write all
internally known cookies to the specified file when \fIcurl_easy_cleanup(3)\fP
is called. If no cookies are known, no file will be created. Specify "-" to
instead have the cookies written to stdout. Using this option also enables
cookies for this session, so if you for example follow a location it will make
matching cookies get sent accordingly.

If the cookie jar file can't be created or written to (when the
\fIcurl_easy_cleanup(3)\fP is called), libcurl will not and cannot report an
error for this. Using \fICURLOPT_VERBOSE\fP or \fICURLOPT_DEBUGFUNCTION\fP
will get a warning to display, but that is the only visible feedback you get
about this possibly lethal situation.
.IP CURLOPT_COOKIESESSION
Pass a long set to 1 to mark this as a new cookie "session". It will force
libcurl to ignore all cookies it is about to load that are "session cookies"
from the previous session. By default, libcurl always stores and loads all
cookies, independent if they are session cookies or not. Session cookies are
cookies without expiry date and they are meant to be alive and existing for
this "session" only.
.IP CURLOPT_COOKIELIST
Pass a char * to a cookie string. Cookie can be either in Netscape / Mozilla
format or just regular HTTP-style header (Set-Cookie: ...) format. If cURL
cookie engine was not enabled it will enable its cookie engine.  Passing a
magic string \&"ALL" will erase all cookies known by cURL. (Added in 7.14.1)
Passing the special string \&"SESS" will only erase all session cookies known
by cURL. (Added in 7.15.4) Passing the special string \&"FLUSH" will write
all cookies known by cURL to the file specified by \fICURLOPT_COOKIEJAR\fP.
(Added in 7.17.1)
.IP CURLOPT_HTTPGET
Pass a long. If the long is 1, this forces the HTTP request to get back
to GET. Usable if a POST, HEAD, PUT, or a custom request has been used
previously using the same curl handle.

When setting \fICURLOPT_HTTPGET\fP to 1, it will automatically set
\fICURLOPT_NOBODY\fP to 0 and \fICURLOPT_UPLOAD\fP to 0.
.IP CURLOPT_HTTP_VERSION
Pass a long, set to one of the values described below. They force libcurl to
use the specific HTTP versions. This is not sensible to do unless you have a
good reason. You have to set this option if you want to use libcurl's HTTP 2.0
support.
.RS
.IP CURL_HTTP_VERSION_NONE
We don't care about what version the library uses. libcurl will use whatever
it thinks fit.
.IP CURL_HTTP_VERSION_1_0
Enforce HTTP 1.0 requests.
.IP CURL_HTTP_VERSION_1_1
Enforce HTTP 1.1 requests.
.IP CURL_HTTP_VERSION_2_0
Attempt HTTP 2.0 requests. libcurl will fall back to HTTP 1.x if HTTP 2.0
can't be negotiated with the server.
.RE
.IP CURLOPT_IGNORE_CONTENT_LENGTH
Ignore the Content-Length header. This is useful for Apache 1.x (and similar
servers) which will report incorrect content length for files over 2
gigabytes. If this option is used, curl will not be able to accurately report
progress, and will simply stop the download when the server ends the
connection. (added in 7.14.1)
.IP CURLOPT_HTTP_CONTENT_DECODING
Pass a long to tell libcurl how to act on content decoding. If set to zero,
content decoding will be disabled. If set to 1 it is enabled. Libcurl has no
default content decoding but requires you to use \fICURLOPT_ACCEPT_ENCODING\fP
for that. (added in 7.16.2)
.IP CURLOPT_HTTP_TRANSFER_DECODING
Pass a long to tell libcurl how to act on transfer decoding. If set to zero,
transfer decoding will be disabled, if set to 1 it is enabled
(default). libcurl does chunked transfer decoding by default unless this
option is set to zero. (added in 7.16.2)
.IP CURLOPT_EXPECT_100_TIMEOUT_MS
Pass a long to tell libcurl the number of milliseconds to wait for a server
response with the HTTP status 100 (Continue), 417 (Expectation Failed) or
similar after sending a HTTP request containing an Expect: 100-continue
header. If this times out before a response is received, the request body is
sent anyway. By default, libcurl waits 1000 milliseconds. (Added in 7.36.0)
.SH SMTP OPTIONS
.IP CURLOPT_MAIL_FROM
Pass a pointer to a zero terminated string as parameter. This should be used
to specify the sender's email address when sending SMTP mail with libcurl.

An originator email address should be specified with angled brackets (<>)
around it, which if not specified, will be added by libcurl from version
7.21.4 onwards. Failing to provide such brackets may cause the server to
reject the email.

If this parameter is not specified then an empty address will be sent to the
mail server which may or may not cause the email to be rejected.

(Added in 7.20.0)
.IP CURLOPT_MAIL_RCPT
Pass a pointer to a linked list of recipients to pass to the server in your
SMTP mail request. The linked list should be a fully valid list of \fBstruct
curl_slist\fP structs properly filled in. Use \fIcurl_slist_append(3)\fP to
create the list and \fIcurl_slist_free_all(3)\fP to clean up an entire list.

When performing a mail transfer, each recipient should be specified within a
pair of angled brackets (<>), however, should you not use an angled bracket as
the first character libcurl will assume you provided a single email address and
enclose that address within brackets for you. (Added in 7.20.0)

When performing an address verification (VRFY command), each recipient should
be specified as the user name or user name and domain (as per Section 3.5 of
RFC5321). (Added in 7.34.0)

When performing a mailing list expand (EXPN command), each recipient should be
specified using the mailing list name, such as "Friends" or "London-Office".
(Added in 7.34.0)
.IP CURLOPT_MAIL_AUTH
Pass a pointer to a zero terminated string as parameter. This will be used
to specify the authentication address (identity) of a submitted message that
is being relayed to another server.

This optional parameter allows co-operating agents in a trusted environment to
communicate the authentication of individual messages and should only be used
by the application program, using libcurl, if the application is itself a
mail server acting in such an environment. If the application is operating as
such and the AUTH address is not known or is invalid, then an empty string
should be used for this parameter.

Unlike CURLOPT_MAIL_FROM and CURLOPT_MAIL_RCPT, the address should not be
specified within a pair of angled brackets (<>). However, if an empty string
is used then a pair of brackets will be sent by libcurl as required by
RFC2554.

(Added in 7.25.0)
.SH TFTP OPTIONS
.IP CURLOPT_TFTP_BLKSIZE
Specify block size to use for TFTP data transmission. Valid range as per
RFC2348 is 8-65464 bytes. The default of 512 bytes will be used if this option
is not specified. The specified block size will only be used pending support
by the remote server. If the server does not return an option acknowledgement
or returns an option acknowledgement with no blksize, the default of 512 bytes
will be used. (added in 7.19.4)
.SH FTP OPTIONS
.IP CURLOPT_FTPPORT
Pass a pointer to a zero terminated string as parameter. It will be used to
get the IP address to use for the FTP PORT instruction. The PORT instruction
tells the remote server to connect to our specified IP address. The string may
be a plain IP address, a host name, a network interface name (under Unix) or
just a '-' symbol to let the library use your system's default IP
address. Default FTP operations are passive, and thus won't use PORT.

The address can be followed by a ':' to specify a port, optionally followed by
a '-' to specify a port range.  If the port specified is 0, the operating
system will pick a free port.  If a range is provided and all ports in the
range are not available, libcurl will report CURLE_FTP_PORT_FAILED for the
handle.  Invalid port/range settings are ignored.  IPv6 addresses followed by
a port or portrange have to be in brackets.  IPv6 addresses without port/range
specifier can be in brackets.  (added in 7.19.5)

Examples with specified ports:

.nf
  eth0:0
  192.168.1.2:32000-33000
  curl.se:32123
  [::1]:1234-4567
.fi

You disable PORT again and go back to using the passive version by setting
this option to NULL.
.IP CURLOPT_QUOTE
Pass a pointer to a linked list of FTP or SFTP commands to pass to the server
prior to your FTP request. This will be done before any other commands are
issued (even before the CWD command for FTP). The linked list should be a
fully valid list of 'struct curl_slist' structs properly filled in with text
strings. Use \fIcurl_slist_append(3)\fP to append strings (commands) to the
list, and clear the entire list afterwards with
\fIcurl_slist_free_all(3)\fP. Disable this operation again by setting a NULL
to this option. When speaking to a FTP (or SFTP since 7.24.0) server, prefix
the command with an asterisk (*) to make libcurl continue even if the command
fails as by default libcurl will stop at first failure.

The set of valid FTP commands depends on the server (see RFC959 for a list of
mandatory commands).

The valid SFTP commands are: chgrp, chmod, chown, ln, mkdir, pwd, rename, rm,
rmdir, symlink (see
.BR curl (1))
(SFTP support added in 7.16.3)
.IP CURLOPT_POSTQUOTE
Pass a pointer to a linked list of FTP or SFTP commands to pass to the server
after your FTP transfer request. The commands will only be run if no error
occurred. The linked list should be a fully valid list of struct curl_slist
structs properly filled in as described for \fICURLOPT_QUOTE\fP. Disable this
operation again by setting a NULL to this option.
.IP CURLOPT_PREQUOTE
Pass a pointer to a linked list of FTP commands to pass to the server after
the transfer type is set. The linked list should be a fully valid list of
struct curl_slist structs properly filled in as described for
\fICURLOPT_QUOTE\fP. Disable this operation again by setting a NULL to this
option. Before version 7.16.0, if you also set \fICURLOPT_NOBODY\fP to 1, this
option didn't work.
.IP CURLOPT_DIRLISTONLY
A parameter set to 1 tells the library to just list the names of files in a
directory, instead of doing a full directory listing that would include file
sizes, dates etc. This works for FTP and SFTP URLs.

This causes an FTP NLST command to be sent on an FTP server.  Beware that some
FTP servers list only files in their response to NLST; they might not include
subdirectories and symbolic links.

Setting this option to 1 also implies a directory listing even if the URL
doesn't end with a slash, which otherwise is necessary.

Do NOT use this option if you also use \fICURLOPT_WILDCARDMATCH\fP as it will
effectively break that feature then.

(This option was known as CURLOPT_FTPLISTONLY up to 7.16.4)
.IP CURLOPT_APPEND
A parameter set to 1 tells the library to append to the remote file instead of
overwrite it. This is only useful when uploading to an FTP site.

(This option was known as CURLOPT_FTPAPPEND up to 7.16.4)
.IP CURLOPT_FTP_USE_EPRT
Pass a long. If the value is 1, it tells curl to use the EPRT (and
LPRT) command when doing active FTP downloads (which is enabled by
\fICURLOPT_FTPPORT\fP). Using EPRT means that it will first attempt to use
EPRT and then LPRT before using PORT, but if you pass zero to this
option, it will not try using EPRT or LPRT, only plain PORT. (Added in 7.10.5)

If the server is an IPv6 host, this option will have no effect as of 7.12.3.
.IP CURLOPT_FTP_USE_EPSV
Pass a long. If the value is 1, it tells curl to use the EPSV command
when doing passive FTP downloads (which it always does by default). Using EPSV
means that it will first attempt to use EPSV before using PASV, but if you
pass zero to this option, it will not try using EPSV, only plain PASV.

If the server is an IPv6 host, this option will have no effect as of 7.12.3.
.IP CURLOPT_FTP_USE_PRET
Pass a long. If the value is 1, it tells curl to send a PRET command before
PASV (and EPSV). Certain FTP servers, mainly drftpd, require this non-standard
command for directory listings as well as up and downloads in PASV mode. Has
no effect when using the active FTP transfers mode.  (Added in 7.20.0)
.IP CURLOPT_FTP_CREATE_MISSING_DIRS
Pass a long. If the value is 1, curl will attempt to create any remote
directory that it fails to CWD into. CWD is the command that changes working
directory. (Added in 7.10.7)

This setting also applies to SFTP-connections. curl will attempt to create
the remote directory if it can't obtain a handle to the target-location. The
creation will fail if a file of the same name as the directory to create
already exists or lack of permissions prevents creation. (Added in 7.16.3)

Starting with 7.19.4, you can also set this value to 2, which will make
libcurl retry the CWD command again if the subsequent MKD command fails. This
is especially useful if you're doing many simultaneous connections against the
same server and they all have this option enabled, as then CWD may first fail
but then another connection does MKD before this connection and thus MKD fails
but trying CWD works! 7.19.4 also introduced the \fICURLFTP_CREATE_DIR\fP and
\fICURLFTP_CREATE_DIR_RETRY\fP enum names for these arguments.

Before version 7.19.4, libcurl will simply ignore arguments set to 2 and act
as if 1 was selected.
.IP CURLOPT_FTP_RESPONSE_TIMEOUT
Pass a long.  Causes curl to set a timeout period (in seconds) on the amount
of time that the server is allowed to take in order to generate a response
message for a command before the session is considered hung.  While curl is
waiting for a response, this value overrides \fICURLOPT_TIMEOUT\fP. It is
recommended that if used in conjunction with \fICURLOPT_TIMEOUT\fP, you set
\fICURLOPT_FTP_RESPONSE_TIMEOUT\fP to a value smaller than
\fICURLOPT_TIMEOUT\fP.  (Added in 7.10.8)
.IP CURLOPT_FTP_ALTERNATIVE_TO_USER
Pass a char * as parameter, pointing to a string which will be used to
authenticate if the usual FTP "USER user" and "PASS password" negotiation
fails. This is currently only known to be required when connecting to
Tumbleweed's Secure Transport FTPS server using client certificates for
authentication. (Added in 7.15.5)
.IP CURLOPT_FTP_SKIP_PASV_IP
Pass a long. If set to 1, it instructs libcurl to not use the IP address the
server suggests in its 227-response to libcurl's PASV command when libcurl
connects the data connection. Instead libcurl will re-use the same IP address
it already uses for the control connection. But it will use the port number
from the 227-response. (Added in 7.14.2)

This option has no effect if PORT, EPRT or EPSV is used instead of PASV.
.IP CURLOPT_FTPSSLAUTH
Pass a long using one of the values from below, to alter how libcurl issues
\&"AUTH TLS" or "AUTH SSL" when FTP over SSL is activated (see
\fICURLOPT_USE_SSL\fP). (Added in 7.12.2)
.RS
.IP CURLFTPAUTH_DEFAULT
Allow libcurl to decide.
.IP CURLFTPAUTH_SSL
Try "AUTH SSL" first, and only if that fails try "AUTH TLS".
.IP CURLFTPAUTH_TLS
Try "AUTH TLS" first, and only if that fails try "AUTH SSL".
.RE
.IP CURLOPT_FTP_SSL_CCC
If enabled, this option makes libcurl use CCC (Clear Command Channel). It
shuts down the SSL/TLS layer after authenticating. The rest of the
control channel communication will be unencrypted. This allows NAT routers
to follow the FTP transaction. Pass a long using one of the values below.
(Added in 7.16.1)
.RS
.IP CURLFTPSSL_CCC_NONE
Don't attempt to use CCC.
.IP CURLFTPSSL_CCC_PASSIVE
Do not initiate the shutdown, but wait for the server to do it. Do not send
a reply.
.IP CURLFTPSSL_CCC_ACTIVE
Initiate the shutdown and wait for a reply.
.RE
.IP CURLOPT_FTP_ACCOUNT
Pass a pointer to a zero terminated string (or NULL to disable). When an FTP
server asks for "account data" after user name and password has been provided,
this data is sent off using the ACCT command. (Added in 7.13.0)
.IP CURLOPT_FTP_FILEMETHOD
Pass a long that should have one of the following values. This option controls
what method libcurl should use to reach a file on a FTP(S) server. The
argument should be one of the following alternatives:
.RS
.IP CURLFTPMETHOD_MULTICWD
libcurl does a single CWD operation for each path part in the given URL. For
deep hierarchies this means many commands. This is how RFC1738 says it
should be done. This is the default but the slowest behavior.
.IP CURLFTPMETHOD_NOCWD
libcurl does no CWD at all. libcurl will do SIZE, RETR, STOR etc and give a
full path to the server for all these commands. This is the fastest behavior.
.IP CURLFTPMETHOD_SINGLECWD
libcurl does one CWD with the full target directory and then operates on the
file \&"normally" (like in the multicwd case). This is somewhat more standards
compliant than 'nocwd' but without the full penalty of 'multicwd'.
.RE
(Added in 7.15.1)
.SH RTSP OPTIONS
.IP CURLOPT_RTSP_REQUEST
Tell libcurl what kind of RTSP request to make. Pass one of the following RTSP
enum values. Unless noted otherwise, commands require the Session ID to be
initialized. (Added in 7.20.0)
.RS
.IP CURL_RTSPREQ_OPTIONS
Used to retrieve the available methods of the server. The application is
responsible for parsing and obeying the response. \fB(The session ID is not
needed for this method.)\fP  (Added in 7.20.0)
.IP CURL_RTSPREQ_DESCRIBE
Used to get the low level description of a stream. The application should note
what formats it understands in the \fI'Accept:'\fP header. Unless set
manually, libcurl will automatically fill in \fI'Accept:
application/sdp'\fP. Time-condition headers will be added to Describe requests
if the \fICURLOPT_TIMECONDITION\fP option is active. \fB(The session ID is not
needed for this method)\fP  (Added in 7.20.0)
.IP CURL_RTSPREQ_ANNOUNCE
When sent by a client, this method changes the description of the session. For
example, if a client is using the server to record a meeting, the client can
use Announce to inform the server of all the meta-information about the
session.  ANNOUNCE acts like a HTTP PUT or POST just like
\fICURL_RTSPREQ_SET_PARAMETER\fP (Added in 7.20.0)
.IP CURL_RTSPREQ_SETUP
Setup is used to initialize the transport layer for the session. The
application must set the desired Transport options for a session by using the
\fICURLOPT_RTSP_TRANSPORT\fP option prior to calling setup. If no session ID
is currently set with \fICURLOPT_RTSP_SESSION_ID\fP, libcurl will extract and
use the session ID in the response to this request. \fB(The session ID is not
needed for this method).\fP  (Added in 7.20.0)
.IP CURL_RTSPREQ_PLAY
Send a Play command to the server. Use the \fICURLOPT_RANGE\fP option to
modify the playback time (e.g. 'npt=10-15').  (Added in 7.20.0)
.IP CURL_RTSPREQ_PAUSE
Send a Pause command to the server. Use the \fICURLOPT_RANGE\fP option with a
single value to indicate when the stream should be halted. (e.g. npt='25')
(Added in 7.20.0)
.IP CURL_RTSPREQ_TEARDOWN
This command terminates an RTSP session. Simply closing a connection does not
terminate the RTSP session since it is valid to control an RTSP session over
different connections.  (Added in 7.20.0)
.IP CURL_RTSPREQ_GET_PARAMETER
Retrieve a parameter from the server. By default, libcurl will automatically
include a \fIContent-Type: text/parameters\fP header on all non-empty requests
unless a custom one is set. GET_PARAMETER acts just like a HTTP PUT or POST
(see \fICURL_RTSPREQ_SET_PARAMETER\fP).
Applications wishing to send a heartbeat message (e.g. in the presence of a
server-specified timeout) should send use an empty GET_PARAMETER request.
(Added in 7.20.0)
.IP CURL_RTSPREQ_SET_PARAMETER
Set a parameter on the server. By default, libcurl will automatically include
a \fIContent-Type: text/parameters\fP header unless a custom one is set. The
interaction with SET_PARAMTER is much like a HTTP PUT or POST. An application
may either use \fICURLOPT_UPLOAD\fP with \fICURLOPT_READDATA\fP like a HTTP
PUT, or it may use \fICURLOPT_POSTFIELDS\fP like a HTTP POST. No chunked
transfers are allowed, so the application must set the
\fICURLOPT_INFILESIZE\fP in the former and \fICURLOPT_POSTFIELDSIZE\fP in the
latter. Also, there is no use of multi-part POSTs within RTSP. (Added in
7.20.0)
.IP CURL_RTSPREQ_RECORD
Used to tell the server to record a session. Use the \fICURLOPT_RANGE\fP
option to modify the record time. (Added in 7.20.0)
.IP CURL_RTSPREQ_RECEIVE
This is a special request because it does not send any data to the server. The
application may call this function in order to receive interleaved RTP
data. It will return after processing one read buffer of data in order to give
the application a chance to run. (Added in 7.20.0)
.RE
.IP CURLOPT_RTSP_SESSION_ID
Pass a char * as a parameter to set the value of the current RTSP Session ID
for the handle. Useful for resuming an in-progress session. Once this value is
set to any non-NULL value, libcurl will return \fICURLE_RTSP_SESSION_ERROR\fP
if ID received from the server does not match. If unset (or set to NULL),
libcurl will automatically set the ID the first time the server sets it in a
response. (Added in 7.20.0)
.IP CURLOPT_RTSP_STREAM_URI
Set the stream URI to operate on by passing a char * . For example, a single
session may be controlling \fIrtsp://foo/twister/audio\fP and
\fIrtsp://foo/twister/video\fP and the application can switch to the
appropriate stream using this option. If unset, libcurl will default to
operating on generic server options by passing '*' in the place of the RTSP
Stream URI. This option is distinct from \fICURLOPT_URL\fP. When working with
RTSP, the \fICURLOPT_STREAM_URI\fP indicates what URL to send to the server in
the request header while the \fICURLOPT_URL\fP indicates where to make the
connection to.  (e.g. the \fICURLOPT_URL\fP for the above examples might be
set to \fIrtsp://foo/twister\fP (Added in 7.20.0)
.IP CURLOPT_RTSP_TRANSPORT
Pass a char * to tell libcurl what to pass for the Transport: header for this
RTSP session. This is mainly a convenience method to avoid needing to set a
custom Transport: header for every SETUP request. The application must set a
Transport: header before issuing a SETUP request. (Added in 7.20.0)
.IP CURLOPT_RTSP_HEADER
This option is simply an alias for \fICURLOPT_HTTP_HEADER\fP. Use this to
replace the standard headers that RTSP and HTTP share. It is also valid to use
the shortcuts such as \fICURLOPT_USERAGENT\fP. (Added in 7.20.0)
.IP CURLOPT_RTSP_CLIENT_CSEQ
Manually set the the CSEQ number to issue for the next RTSP request. Useful if
the application is resuming a previously broken connection. The CSEQ will
increment from this new number henceforth. (Added in 7.20.0)
.IP CURLOPT_RTSP_SERVER_CSEQ
Manually set the CSEQ number to expect for the next RTSP Server->Client
request.  At the moment, this feature (listening for Server requests) is
unimplemented. (Added in 7.20.0)
.SH PROTOCOL OPTIONS
.IP CURLOPT_TRANSFERTEXT
A parameter set to 1 tells the library to use ASCII mode for FTP transfers,
instead of the default binary transfer. For win32 systems it does not set the
stdout to binary mode. This option can be usable when transferring text data
between systems with different views on certain characters, such as newlines
or similar.

libcurl does not do a complete ASCII conversion when doing ASCII transfers
over FTP. This is a known limitation/flaw that nobody has rectified. libcurl
simply sets the mode to ASCII and performs a standard transfer.
.IP CURLOPT_PROXY_TRANSFER_MODE
Pass a long. If the value is set to 1 (one), it tells libcurl to set the
transfer mode (binary or ASCII) for FTP transfers done via a HTTP proxy, by
appending ;type=a or ;type=i to the URL. Without this setting, or it being set
to 0 (zero, the default), \fICURLOPT_TRANSFERTEXT\fP has no effect when doing
FTP via a proxy. Beware that not all proxies support this feature.  (Added in
7.18.0)
.IP CURLOPT_CRLF
Pass a long. If the value is set to 1 (one), libcurl converts Unix newlines to
CRLF newlines on transfers. Disable this option again by setting the value to
0 (zero).
.IP CURLOPT_RANGE
Pass a char * as parameter, which should contain the specified range you
want. It should be in the format "X-Y", where X or Y may be left out. HTTP
transfers also support several intervals, separated with commas as in
\fI"X-Y,N-M"\fP. Using this kind of multiple intervals will cause the HTTP
server to send the response document in pieces (using standard MIME separation
techniques). For RTSP, the formatting of a range should follow RFC2326
Section 12.29. For RTSP, byte ranges are \fBnot\fP permitted. Instead, ranges
should be given in npt, utc, or smpte formats.

Pass a NULL to this option to disable the use of ranges.

Ranges work on HTTP, FTP, FILE (since 7.18.0), and RTSP (since 7.20.0)
transfers only.
.IP CURLOPT_RESUME_FROM
Pass a long as parameter. It contains the offset in number of bytes that you
want the transfer to start from. Set this option to 0 to make the transfer
start from the beginning (effectively disabling resume). For FTP, set this
option to -1 to make the transfer start from the end of the target file
(useful to continue an interrupted upload).

When doing uploads with FTP, the resume position is where in the local/source
file libcurl should try to resume the upload from and it will then append the
source file to the remote target file.
.IP CURLOPT_RESUME_FROM_LARGE
Pass a curl_off_t as parameter. It contains the offset in number of bytes that
you want the transfer to start from. (Added in 7.11.0)
.IP CURLOPT_CUSTOMREQUEST
Pass a pointer to a zero terminated string as parameter.

When you change the request method by setting \fBCURLOPT_CUSTOMREQUEST\fP to
something, you don't actually change how libcurl behaves or acts in regards
to the particular request method, it will only change the actual string sent
in the request.

Restore to the internal default by setting this to NULL.

This option can be used to specify the request:

.B HTTP

Instead of GET or HEAD when performing HTTP based requests. This is
particularly useful, for example, for performing a HTTP DELETE request.

For example:

When you tell libcurl to do a HEAD request, but then specify a GET though a
custom request libcurl will still act as if it sent a HEAD. To switch to a
proper HEAD use \fICURLOPT_NOBODY\fP, to switch to a proper POST use
\fICURLOPT_POST\fP or \fICURLOPT_POSTFIELDS\fP and to switch to a proper GET
use CURLOPT_HTTPGET.

Please don't perform this at will, on HTTP based requests, by making sure
your server supports the command you are sending first.

Many people have wrongly used this option to replace the entire request with
their own, including multiple headers and POST contents. While that might
work in many cases, it will cause libcurl to send invalid requests and it
could possibly confuse the remote server badly. Use \fICURLOPT_POST\fP and
\fICURLOPT_POSTFIELDS\fP to set POST data. Use \fICURLOPT_HTTPHEADER\fP to
replace or extend the set of headers sent by libcurl. Use
\fICURLOPT_HTTP_VERSION\fP to change HTTP version.

.B FTP

Instead of LIST and NLST when performing FTP directory listings.

.B IMAP

Instead of LIST when issuing IMAP based requests. (Added in 7.30.0)

.B POP3

Instead of LIST and RETR when issuing POP3 based requests. (Added in 7.26.0)

For example:

When you tell libcurl to use a custom request it will behave like a LIST or
RETR command was sent where it expects data to be returned by the server. As
such \fICURLOPT_NOBODY\fP should be used when specifying commands such as
DELE and NOOP for example.

.B SMTP

Instead of a HELP or VRFY when issuing SMTP based requests. (Added in 7.34.0)

For example:

Normally a multiline response is returned which can be used, in conjuection with
\fICURLOPT_MAIL_RCPT\fP, to specify an EXPN request. If the \fICURLOPT_NOBODY\fP
option is specified then the request can be used to issue NOOP and RSET
commands.
.IP CURLOPT_FILETIME
Pass a long. If it is 1, libcurl will attempt to get the modification date of
the remote document in this operation. This requires that the remote server
sends the time or replies to a time querying command. The
\fIcurl_easy_getinfo(3)\fP function with the \fICURLINFO_FILETIME\fP argument
can be used after a transfer to extract the received time (if any).
.IP CURLOPT_NOBODY
A parameter set to 1 tells the library to not include the body-part in the
output. This is only relevant for protocols that have separate header and
body parts. On HTTP(S) servers, this will make libcurl do a HEAD request.

To change request to GET, you should use \fICURLOPT_HTTPGET\fP. Change
request to POST with \fICURLOPT_POST\fP etc.
.IP CURLOPT_INFILESIZE
When uploading a file to a remote site, this option should be used to tell
libcurl what the expected size of the infile is. This value should be passed
as a long. See also \fICURLOPT_INFILESIZE_LARGE\fP.

For uploading using SCP, this option or \fICURLOPT_INFILESIZE_LARGE\fP is
mandatory.

To "unset" this value again, set it to -1.

When sending emails using SMTP, this command can be used to specify the
optional SIZE parameter for the MAIL FROM command. (Added in 7.23.0)

This option does not limit how much data libcurl will actually send, as that
is controlled entirely by what the read callback returns.
.IP CURLOPT_INFILESIZE_LARGE
When uploading a file to a remote site, this option should be used to tell
libcurl what the expected size of the infile is.  This value should be passed
as a curl_off_t. (Added in 7.11.0)

For uploading using SCP, this option or \fICURLOPT_INFILESIZE\fP is mandatory.

To "unset" this value again, set it to -1.

When sending emails using SMTP, this command can be used to specify the
optional SIZE parameter for the MAIL FROM command. (Added in 7.23.0)

This option does not limit how much data libcurl will actually send, as that
is controlled entirely by what the read callback returns.
.IP CURLOPT_UPLOAD
A parameter set to 1 tells the library to prepare for an upload. The
\fICURLOPT_READDATA\fP and \fICURLOPT_INFILESIZE\fP or
\fICURLOPT_INFILESIZE_LARGE\fP options are also interesting for uploads. If
the protocol is HTTP, uploading means using the PUT request unless you tell
libcurl otherwise.

Using PUT with HTTP 1.1 implies the use of a "Expect: 100-continue" header.
You can disable this header with \fICURLOPT_HTTPHEADER\fP as usual.

If you use PUT to a HTTP 1.1 server, you can upload data without knowing the
size before starting the transfer if you use chunked encoding. You enable this
by adding a header like "Transfer-Encoding: chunked" with
\fICURLOPT_HTTPHEADER\fP. With HTTP 1.0 or without chunked transfer, you must
specify the size.
.IP CURLOPT_MAXFILESIZE
Pass a long as parameter. This allows you to specify the maximum size (in
bytes) of a file to download. If the file requested is larger than this value,
the transfer will not start and CURLE_FILESIZE_EXCEEDED will be returned.

The file size is not always known prior to download, and for such files this
option has no effect even if the file transfer ends up being larger than this
given limit. This concerns both FTP and HTTP transfers.
.IP CURLOPT_MAXFILESIZE_LARGE
Pass a curl_off_t as parameter. This allows you to specify the maximum size
(in bytes) of a file to download. If the file requested is larger than this
value, the transfer will not start and \fICURLE_FILESIZE_EXCEEDED\fP will be
returned. (Added in 7.11.0)

The file size is not always known prior to download, and for such files this
option has no effect even if the file transfer ends up being larger than this
given limit. This concerns both FTP and HTTP transfers.
.IP CURLOPT_TIMECONDITION
Pass a long as parameter. This defines how the \fICURLOPT_TIMEVALUE\fP time
value is treated. You can set this parameter to \fICURL_TIMECOND_IFMODSINCE\fP
or \fICURL_TIMECOND_IFUNMODSINCE\fP. This feature applies to HTTP, FTP, RTSP,
and FILE.

The last modification time of a file is not always known and in such instances
this feature will have no effect even if the given time condition would not
have been met. \fIcurl_easy_getinfo(3)\fP with the
\fICURLINFO_CONDITION_UNMET\fP option can be used after a transfer to learn if
a zero-byte successful "transfer" was due to this condition not matching.
.IP CURLOPT_TIMEVALUE
Pass a long as parameter. This should be the time in seconds since 1 Jan 1970,
and the time will be used in a condition as specified with
\fICURLOPT_TIMECONDITION\fP.
.SH CONNECTION OPTIONS
.IP CURLOPT_TIMEOUT
Pass a long as parameter containing the maximum time in seconds that you allow
the libcurl transfer operation to take. Normally, name lookups can take a
considerable time and limiting operations to less than a few minutes risk
aborting perfectly normal operations. This option will cause curl to use the
SIGALRM to enable time-outing system calls.

In unix-like systems, this might cause signals to be used unless
\fICURLOPT_NOSIGNAL\fP is set.

Default timeout is 0 (zero) which means it never times out.
.IP CURLOPT_TIMEOUT_MS
An alternative to \fICURLOPT_TIMEOUT\fP but takes number of milliseconds
instead. If libcurl is built to use the standard system name resolver, that
portion of the transfer will still use full-second resolution for timeouts
with a minimum timeout allowed of one second.

If both \fICURLOPT_TIMEOUT\fP and \fICURLOPT_TIMEOUT_MS\fP are set, the value
set last will be used.

(Added in 7.16.2)
.IP CURLOPT_LOW_SPEED_LIMIT
Pass a long as parameter. It contains the transfer speed in bytes per second
that the transfer should be below during \fICURLOPT_LOW_SPEED_TIME\fP seconds
for the library to consider it too slow and abort.
.IP CURLOPT_LOW_SPEED_TIME
Pass a long as parameter. It contains the time in seconds that the transfer
should be below the \fICURLOPT_LOW_SPEED_LIMIT\fP for the library to consider
it too slow and abort.
.IP CURLOPT_MAX_SEND_SPEED_LARGE
Pass a curl_off_t as parameter.  If an upload exceeds this speed (counted in
bytes per second) on cumulative average during the transfer, the transfer will
pause to keep the average rate less than or equal to the parameter value.
Defaults to unlimited speed.

This option doesn't affect transfer speeds done with FILE:// URLs. (Added in
 7.15.5)
.IP CURLOPT_MAX_RECV_SPEED_LARGE
Pass a curl_off_t as parameter.  If a download exceeds this speed (counted in
bytes per second) on cumulative average during the transfer, the transfer will
pause to keep the average rate less than or equal to the parameter
value. Defaults to unlimited speed.

This option doesn't affect transfer speeds done with FILE:// URLs. (Added in
7.15.5)
.IP CURLOPT_MAXCONNECTS
Pass a long. The set number will be the persistent connection cache size. The
set amount will be the maximum amount of simultaneously open connections that
libcurl may cache in this easy handle. Default is 5, and there isn't much
point in changing this value unless you are perfectly aware of how this works
and changes libcurl's behaviour. This concerns connections using any of the
protocols that support persistent connections.

When reaching the maximum limit, curl closes the oldest one in the cache to
prevent increasing the number of open connections.

If you already have performed transfers with this curl handle, setting a
smaller MAXCONNECTS than before may cause open connections to get closed
unnecessarily.

If you add this easy handle to a multi handle, this setting is not
acknowledged, and you must instead use \fIcurl_multi_setopt(3)\fP and the
\fICURLMOPT_MAXCONNECTS\fP option.
.IP CURLOPT_CLOSEPOLICY
(Obsolete) This option does nothing.
.IP CURLOPT_FRESH_CONNECT
Pass a long. Set to 1 to make the next transfer use a new (fresh) connection
by force. If the connection cache is full before this connection, one of the
existing connections will be closed as according to the selected or default
policy. This option should be used with caution and only if you understand
what it does. Set this to 0 to have libcurl attempt re-using an existing
connection (default behavior).
.IP CURLOPT_FORBID_REUSE
Pass a long. Set to 1 to make the next transfer explicitly close the
connection when done. Normally, libcurl keeps all connections alive when done
with one transfer in case a succeeding one follows that can re-use them.
This option should be used with caution and only if you understand what it
does. Set to 0 to have libcurl keep the connection open for possible later
re-use (default behavior).
.IP CURLOPT_CONNECTTIMEOUT
Pass a long. It should contain the maximum time in seconds that you allow the
connection to the server to take.  This only limits the connection phase, once
it has connected, this option is of no more use. Set to zero to switch to the
default built-in connection timeout - 300 seconds. See also the
\fICURLOPT_TIMEOUT\fP option.

In unix-like systems, this might cause signals to be used unless
\fICURLOPT_NOSIGNAL\fP is set.
.IP CURLOPT_CONNECTTIMEOUT_MS
Like \fICURLOPT_CONNECTTIMEOUT\fP but takes the number of milliseconds
instead. If libcurl is built to use the standard system name resolver,
that portion of the connect will still use full-second resolution for
timeouts with a minimum timeout allowed of one second.
(Added in 7.16.2)
.IP CURLOPT_IPRESOLVE
Allows an application to select what kind of IP addresses to use when
resolving host names. This is only interesting when using host names that
resolve addresses using more than one version of IP. The allowed values are:
.RS
.IP CURL_IPRESOLVE_WHATEVER
Default, resolves addresses to all IP versions that your system allows.
.IP CURL_IPRESOLVE_V4
Resolve to IPv4 addresses.
.IP CURL_IPRESOLVE_V6
Resolve to IPv6 addresses.
.RE
.IP CURLOPT_CONNECT_ONLY
Pass a long. If the parameter equals 1, it tells the library to perform all
the required proxy authentication and connection setup, but no data transfer.
This option is implemented for HTTP, SMTP and POP3.

The option can be used to simply test a connection to a server, but is more
useful when used with the \fICURLINFO_LASTSOCKET\fP option to
\fIcurl_easy_getinfo(3)\fP as the library can set up the connection and then
the application can obtain the most recently used socket for special data
transfers. (Added in 7.15.2)
.IP CURLOPT_USE_SSL
Pass a long using one of the values from below, to make libcurl use your
desired level of SSL for the transfer. (Added in 7.11.0)

This is for enabling SSL/TLS when you use FTP, SMTP, POP3, IMAP etc.

(This option was known as CURLOPT_FTP_SSL up to 7.16.4, and the constants
were known as CURLFTPSSL_*)
.RS
.IP CURLUSESSL_NONE
Don't attempt to use SSL.
.IP CURLUSESSL_TRY
Try using SSL, proceed as normal otherwise.
.IP CURLUSESSL_CONTROL
Require SSL for the control connection or fail with \fICURLE_USE_SSL_FAILED\fP.
.IP CURLUSESSL_ALL
Require SSL for all communication or fail with \fICURLE_USE_SSL_FAILED\fP.
.RE
.IP CURLOPT_RESOLVE
Pass a pointer to a linked list of strings with host name resolve information
to use for requests with this handle. The linked list should be a fully valid
list of \fBstruct curl_slist\fP structs properly filled in. Use
\fIcurl_slist_append(3)\fP to create the list and \fIcurl_slist_free_all(3)\fP
to clean up an entire list.

Each single name resolve string should be written using the format
HOST:PORT:ADDRESS where HOST is the name libcurl will try to resolve, PORT is
the port number of the service where libcurl wants to connect to the HOST and
ADDRESS is the numerical IP address. If libcurl is built to support IPv6,
ADDRESS can of course be either IPv4 or IPv6 style addressing.

This option effectively pre-populates the DNS cache with entries for the
host+port pair so redirects and everything that operations against the
HOST+PORT will instead use your provided ADDRESS. Addresses to set with
\fICURL_RESOLVE\fP will not time-out from the DNS cache like ordindary
entries.

You can remove names from the DNS cache again, to stop providing these fake
resolves, by including a string in the linked list that uses the format
\&"-HOST:PORT". The host name must be prefixed with a dash, and the host name
and port number must exactly match what was already added previously.

(Added in 7.21.3)
.IP CURLOPT_DNS_SERVERS
Set the list of DNS servers to be used instead of the system default.
The format of the dns servers option is:

host[:port][,host[:port]]...

For example:

192.168.1.100,192.168.1.101,3.4.5.6

This option requires that libcurl was built with a resolver backend that
supports this operation. The c-ares backend is the only such one.

(Added in 7.24.0)
.IP CURLOPT_DNS_INTERFACE
Pass a char * as parameter. Set the name of the network interface that
the DNS resolver should bind to. This must be an interface name (not an
address). Set this option to NULL to use the default setting (don't
bind to a specific interface).

This option requires that libcurl was built with a resolver backend that
supports this operation. The c-ares backend is the only such one.

(Added in 7.33.0)
.IP CURLOPT_DNS_LOCAL_IP4
Set the local IPv4 address that the resolver should bind to. The argument
should be of type char * and contain a single IPv4 address as a string.
Set this option to NULL to use the default setting (don't
bind to a specific IP address).

This option requires that libcurl was built with a resolver backend that
supports this operation. The c-ares backend is the only such one.

(Added in 7.33.0)
.IP CURLOPT_DNS_LOCAL_IP6
Set the local IPv6 address that the resolver should bind to. The argument
should be of type char * and contain a single IPv6 address as a string.
Set this option to NULL to use the default setting (don't
bind to a specific IP address).

This option requires that libcurl was built with a resolver backend that
supports this operation. The c-ares backend is the only such one.

(Added in 7.33.0)
.IP CURLOPT_ACCEPTTIMEOUT_MS
Pass a long telling libcurl the maximum number of milliseconds to wait for a
server to connect back to libcurl when an active FTP connection is used. If no
timeout is set, the internal default of 60000 will be used. (Added in 7.24.0)
.SH SSL and SECURITY OPTIONS
.IP CURLOPT_SSLCERT
Pass a pointer to a zero terminated string as parameter. The string should be
the file name of your certificate. The default format is "P12" on Secure
Transport and "PEM" on other engines, and can be changed with
\fICURLOPT_SSLCERTTYPE\fP.

With NSS or Secure Transport, this can also be the nickname of the certificate
you wish to authenticate with as it is named in the security database. If you
want to use a file from the current directory, please precede it with "./"
prefix, in order to avoid confusion with a nickname.
.IP CURLOPT_SSLCERTTYPE
Pass a pointer to a zero terminated string as parameter. The string should be
the format of your certificate. Supported formats are "PEM" and "DER", except
with Secure Transport. OpenSSL (versions 0.9.3 and later) and Secure Transport
(on iOS 5 or later, or OS X 10.7 or later) also support "P12" for
PKCS#12-encoded files. (Added in 7.9.3)
.IP CURLOPT_SSLKEY
Pass a pointer to a zero terminated string as parameter. The string should be
the file name of your private key. The default format is "PEM" and can be
changed with \fICURLOPT_SSLKEYTYPE\fP.

(iOS and Mac OS X only) This option is ignored if curl was built against Secure
Transport. Secure Transport expects the private key to be already present in
the keychain or PKCS#12 file containing the certificate.
.IP CURLOPT_SSLKEYTYPE
Pass a pointer to a zero terminated string as parameter. The string should be
the format of your private key. Supported formats are "PEM", "DER" and "ENG".

The format "ENG" enables you to load the private key from a crypto engine. In
this case \fICURLOPT_SSLKEY\fP is used as an identifier passed to the
engine. You have to set the crypto engine with \fICURLOPT_SSLENGINE\fP.
\&"DER" format key file currently does not work because of a bug in OpenSSL.
.IP CURLOPT_KEYPASSWD
Pass a pointer to a zero terminated string as parameter. It will be used as
the password required to use the \fICURLOPT_SSLKEY\fP or
\fICURLOPT_SSH_PRIVATE_KEYFILE\fP private key.
You never needed a pass phrase to load a certificate but you need one to
load your private key.

(This option was known as CURLOPT_SSLKEYPASSWD up to 7.16.4 and
CURLOPT_SSLCERTPASSWD up to 7.9.2)
.IP CURLOPT_SSL_ENABLE_ALPN
Pass a long as parameter, 0 or 1 where 1 is for enable and 0 for disable. By
default, libcurl assumes a value of 1. This option enables/disables ALPN in
the SSL handshake (if the SSL backend libcurl is built to use supports it),
which can be used to negotiate http2.

(Added in 7.36.0)
.IP CURLOPT_SSL_ENABLE_NPN
Pass a long as parameter, 0 or 1 where 1 is for enable and 0 for disable. By
default, libcurl assumes a value of 1. This option enables/disables NPN in the
SSL handshake (if the SSL backend libcurl is built to use supports it), which
can be used to negotiate http2.

(Added in 7.36.0)
.IP CURLOPT_SSLENGINE
Pass a pointer to a zero terminated string as parameter. It will be used as
the identifier for the crypto engine you want to use for your private
key.

If the crypto device cannot be loaded, \fICURLE_SSL_ENGINE_NOTFOUND\fP is
returned.
.IP CURLOPT_SSLENGINE_DEFAULT
Sets the actual crypto engine as the default for (asymmetric) crypto
operations.

If the crypto device cannot be set, \fICURLE_SSL_ENGINE_SETFAILED\fP is
returned.

Even though this option doesn't need any parameter, in some configurations
\fIcurl_easy_setopt\fP might be defined as a macro taking exactly three
arguments. Therefore, it's recommended to pass 1 as parameter to this option.
.IP CURLOPT_SSLVERSION
Pass a long as parameter to control what version of SSL/TLS to attempt to use.
(Added in 7.9.2)

The available options are:
.RS
.IP CURL_SSLVERSION_DEFAULT
The default action. This will attempt to figure out the remote SSL protocol
version, i.e. either SSLv3 or TLSv1 (but not SSLv2, which became disabled
by default with 7.18.1).
.IP CURL_SSLVERSION_TLSv1
Force TLSv1.x
.IP CURL_SSLVERSION_SSLv2
Force SSLv2
.IP CURL_SSLVERSION_SSLv3
Force SSLv3
.IP CURL_SSLVERSION_TLSv1_0
Force TLSv1.0 (Added in 7.34.0)
.IP CURL_SSLVERSION_TLSv1_1
Force TLSv1.1 (Added in 7.34.0)
.IP CURL_SSLVERSION_TLSv1_2
Force TLSv1.2 (Added in 7.34.0)
.RE
.IP CURLOPT_SSL_VERIFYPEER
Pass a long as parameter. By default, curl assumes a value of 1.

This option determines whether curl verifies the authenticity of the peer's
certificate. A value of 1 means curl verifies; 0 (zero) means it doesn't.

When negotiating a SSL connection, the server sends a certificate indicating
its identity.  Curl verifies whether the certificate is authentic, i.e. that
you can trust that the server is who the certificate says it is.  This trust
is based on a chain of digital signatures, rooted in certification authority
(CA) certificates you supply.  curl uses a default bundle of CA certificates
(the path for that is determined at build time) and you can specify alternate
certificates with the \fICURLOPT_CAINFO\fP option or the \fICURLOPT_CAPATH\fP
option.

When \fICURLOPT_SSL_VERIFYPEER\fP is nonzero, and the verification fails to
prove that the certificate is authentic, the connection fails.  When the
option is zero, the peer certificate verification succeeds regardless.

Authenticating the certificate is not by itself very useful.  You typically
want to ensure that the server, as authentically identified by its
certificate, is the server you mean to be talking to.  Use
\fICURLOPT_SSL_VERIFYHOST\fP to control that. The check that the host name in
the certificate is valid for the host name you're connecting to is done
independently of the \fICURLOPT_SSL_VERIFYPEER\fP option.
.IP CURLOPT_CAINFO
Pass a char * to a zero terminated string naming a file holding one or more
certificates to verify the peer with.  This makes sense only when used in
combination with the \fICURLOPT_SSL_VERIFYPEER\fP option.  If
\fICURLOPT_SSL_VERIFYPEER\fP is zero, \fICURLOPT_CAINFO\fP need not
even indicate an accessible file.

This option is by default set to the system path where libcurl's cacert bundle
is assumed to be stored, as established at build time.

If curl is built against the NSS SSL library, the NSS PEM PKCS#11 module
(libnsspem.so) needs to be available for this option to work properly.
.IP CURLOPT_ISSUERCERT
Pass a char * to a zero terminated string naming a file holding a CA
certificate in PEM format. If the option is set, an additional check against
the peer certificate is performed to verify the issuer is indeed the one
associated with the certificate provided by the option. This additional check
is useful in multi-level PKI where one needs to enforce that the peer
certificate is from a specific branch of the tree.

This option makes sense only when used in combination with the
\fICURLOPT_SSL_VERIFYPEER\fP option. Otherwise, the result of the check is not
considered as failure.

A specific error code (CURLE_SSL_ISSUER_ERROR) is defined with the option,
which is returned if the setup of the SSL/TLS session has failed due to a
mismatch with the issuer of peer certificate (\fICURLOPT_SSL_VERIFYPEER\fP has
to be set too for the check to fail). (Added in 7.19.0)
.IP CURLOPT_CAPATH
Pass a char * to a zero terminated string naming a directory holding multiple
CA certificates to verify the peer with. If libcurl is built against OpenSSL,
the certificate directory must be prepared using the openssl c_rehash utility.
This makes sense only when used in combination with the
\fICURLOPT_SSL_VERIFYPEER\fP option.  If \fICURLOPT_SSL_VERIFYPEER\fP is zero,
\fICURLOPT_CAPATH\fP need not even indicate an accessible path.  The
\fICURLOPT_CAPATH\fP function apparently does not work in Windows due to some
limitation in openssl. This option is OpenSSL-specific and does nothing if
libcurl is built to use GnuTLS. NSS-powered libcurl provides the option only
for backward compatibility.
.IP CURLOPT_CRLFILE
Pass a char * to a zero terminated string naming a file with the concatenation
of CRL (in PEM format) to use in the certificate validation that occurs during
the SSL exchange.

When curl is built to use NSS or GnuTLS, there is no way to influence the use
of CRL passed to help in the verification process. When libcurl is built with
OpenSSL support, X509_V_FLAG_CRL_CHECK and X509_V_FLAG_CRL_CHECK_ALL are both
set, requiring CRL check against all the elements of the certificate chain if
a CRL file is passed.

This option makes sense only when used in combination with the
\fICURLOPT_SSL_VERIFYPEER\fP option.

A specific error code (CURLE_SSL_CRL_BADFILE) is defined with the option. It
is returned when the SSL exchange fails because the CRL file cannot be loaded.
A failure in certificate verification due to a revocation information found in
the CRL does not trigger this specific error. (Added in 7.19.0)
.IP CURLOPT_SSL_VERIFYHOST
Pass a long as parameter.

This option determines whether libcurl verifies that the server cert is for
the server it is known as.

When negotiating a SSL connection, the server sends a certificate indicating
its identity.

When \fICURLOPT_SSL_VERIFYHOST\fP is 2, that certificate must indicate that
the server is the server to which you meant to connect, or the connection
fails.

Curl considers the server the intended one when the Common Name field or a
Subject Alternate Name field in the certificate matches the host name in the
URL to which you told Curl to connect.

When the value is 1, \fIcurl_easy_setopt\fP will return an error and the option
value will not be changed.  It was previously (in 7.28.0 and earlier) a debug
option of some sorts, but it is no longer supported due to frequently leading
to programmer mistakes.

When the value is 0, the connection succeeds regardless of the names in the
certificate.

The default value for this option is 2.

This option controls checking the server's certificate's claimed identity.
The server could be lying.  To control lying, see
\fICURLOPT_SSL_VERIFYPEER\fP.  If libcurl is built against NSS and
\fICURLOPT_SSL_VERIFYPEER\fP is zero, \fICURLOPT_SSL_VERIFYHOST\fP is also set
to zero and cannot be overridden.
.IP CURLOPT_CERTINFO
Pass a long set to 1 to enable libcurl's certificate chain info gatherer. With
this enabled, libcurl (if built with OpenSSL, NSS, GSKit or QsoSSL) will
extract lots of information
and data about the certificates in the certificate chain used in the SSL
connection. This data may then be retrieved after a transfer using
\fIcurl_easy_getinfo(3)\fP and its option \fICURLINFO_CERTINFO\fP. (Added in
7.19.1)
.IP CURLOPT_RANDOM_FILE
Pass a char * to a zero terminated file name. The file will be used to read
from to seed the random engine for SSL. The more random the specified file is,
the more secure the SSL connection will become.
.IP CURLOPT_EGDSOCKET
Pass a char * to the zero terminated path name to the Entropy Gathering Daemon
socket. It will be used to seed the random engine for SSL.
.IP CURLOPT_SSL_CIPHER_LIST
Pass a char *, pointing to a zero terminated string holding the list of
ciphers to use for the SSL connection. The list must be syntactically correct,
it consists of one or more cipher strings separated by colons. Commas or
spaces are also acceptable separators but colons are normally used, \&!, \&-
and \&+ can be used as operators.

For OpenSSL and GnuTLS valid examples of cipher lists include 'RC4-SHA',
\'SHA1+DES\', 'TLSv1' and 'DEFAULT'. The default list is normally set when you
compile OpenSSL.

You'll find more details about cipher lists on this URL:
\fIhttp://www.openssl.org/docs/apps/ciphers.html\fP

For NSS, valid examples of cipher lists include 'rsa_rc4_128_md5',
\'rsa_aes_128_sha\', etc. With NSS you don't add/remove ciphers. If one uses
this option then all known ciphers are disabled and only those passed in
are enabled.

You'll find more details about the NSS cipher lists on this URL:
\fIhttp://git.fedorahosted.org/cgit/mod_nss.git/plain/docs/mod_nss.html#Directives\fP

.IP CURLOPT_SSL_SESSIONID_CACHE
Pass a long set to 0 to disable libcurl's use of SSL session-ID caching. Set
this to 1 to enable it. By default all transfers are done using the
cache. While nothing ever should get hurt by attempting to reuse SSL
session-IDs, there seem to be broken SSL implementations in the wild that may
require you to disable this in order for you to succeed. (Added in 7.16.0)
.IP CURLOPT_SSL_OPTIONS
Pass a long with a bitmask to tell libcurl about specific SSL behaviors.

CURLSSLOPT_ALLOW_BEAST is the only supported bit and by setting this the user
will tell libcurl to not attempt to use any workarounds for a security flaw
in the SSL3 and TLS1.0 protocols.  If this option isn't used or this bit is
set to 0, the SSL layer libcurl uses may use a work-around for this flaw
although it might cause interoperability problems with some (older) SSL
implementations. WARNING: avoiding this work-around loosens the security, and
by setting this option to 1 you ask for exactly that. (Added in 7.25.0)
.IP CURLOPT_KRBLEVEL
Pass a char * as parameter. Set the kerberos security level for FTP; this also
enables kerberos awareness.  This is a string, \&'clear', \&'safe',
\&'confidential' or \&'private'.  If the string is set but doesn't match one
of these, 'private' will be used. Set the string to NULL to disable kerberos
support for FTP.

(This option was known as CURLOPT_KRB4LEVEL up to 7.16.3)
.IP CURLOPT_GSSAPI_DELEGATION
Set the parameter to CURLGSSAPI_DELEGATION_FLAG to allow unconditional GSSAPI
credential delegation.  The delegation is disabled by default since 7.21.7.
Set the parameter to CURLGSSAPI_DELEGATION_POLICY_FLAG to delegate only if
the OK-AS-DELEGATE flag is set in the service ticket in case this feature is
supported by the GSSAPI implementation and the definition of
GSS_C_DELEG_POLICY_FLAG was available at compile-time.
(Added in 7.22.0)
.SH SSH OPTIONS
.IP CURLOPT_SSH_AUTH_TYPES
Pass a long set to a bitmask consisting of one or more of
CURLSSH_AUTH_PUBLICKEY, CURLSSH_AUTH_PASSWORD, CURLSSH_AUTH_HOST,
CURLSSH_AUTH_KEYBOARD and CURLSSH_AUTH_AGENT. Set CURLSSH_AUTH_ANY to let
libcurl pick a suitable one. Currently CURLSSH_AUTH_HOST has no effect. (Added
in 7.16.1) If CURLSSH_AUTH_AGENT is used, libcurl attempts to connect to
ssh-agent or pageant and let the agent attempt the authentication. (Added in
7.28.0)
.IP CURLOPT_SSH_HOST_PUBLIC_KEY_MD5
Pass a char * pointing to a string containing 32 hexadecimal digits. The
string should be the 128 bit MD5 checksum of the remote host's public key, and
libcurl will reject the connection to the host unless the md5sums match. This
option is only for SCP and SFTP transfers. (Added in 7.17.1)
.IP CURLOPT_SSH_PUBLIC_KEYFILE
Pass a char * pointing to a file name for your public key. If not used,
libcurl defaults to \fB$HOME/.ssh/id_dsa.pub\fP if the HOME environment
variable is set, and just "id_dsa.pub" in the current directory if HOME is not
set.  (Added in 7.16.1)
If an empty string is passed, libcurl will pass no public key to libssh2
which then tries to compute it from the private key, this is known to work
when libssh2 1.4.0+ is linked against OpenSSL. (Added in 7.26.0)
.IP CURLOPT_SSH_PRIVATE_KEYFILE
Pass a char * pointing to a file name for your private key. If not used,
libcurl defaults to \fB$HOME/.ssh/id_dsa\fP if the HOME environment variable
is set, and just "id_dsa" in the current directory if HOME is not set.  If the
file is password-protected, set the password with
\fICURLOPT_KEYPASSWD\fP. (Added in 7.16.1)
.IP CURLOPT_SSH_KNOWNHOSTS
Pass a pointer to a zero terminated string holding the file name of the
known_host file to use.  The known_hosts file should use the OpenSSH file
format as supported by libssh2. If this file is specified, libcurl will only
accept connections with hosts that are known and present in that file, with a
matching public key. Use \fICURLOPT_SSH_KEYFUNCTION\fP to alter the default
behavior on host and key (mis)matching. (Added in 7.19.6)
.IP CURLOPT_SSH_KEYFUNCTION
Pass a pointer to a curl_sshkeycallback function. It gets called when the
known_host matching has been done, to allow the application to act and decide
for libcurl how to proceed. The callback will only be called if
\fICURLOPT_SSH_KNOWNHOSTS\fP is also set.

.nf
int curl_sshkeycallback (CURL *easy,     /* easy handle */
                         const struct curl_khkey *knownkey, /* known */
                         const struct curl_khkey *foundkey, /* found */
                         enum curl_khmatch, /* libcurl's view on the keys */
                         void *clientp);
.fi

The curl_sshkeycallback function gets passed the CURL handle, the key from the
known_hosts file, the key from the remote site, info from libcurl on the
matching status and a custom pointer (set with \fICURLOPT_SSH_KEYDATA\fP). It
MUST return one of the following return codes to tell libcurl how to act:
.RS
.IP CURLKHSTAT_FINE_ADD_TO_FILE
The host+key is accepted and libcurl will append it to the known_hosts file
before continuing with the connection. This will also add the host+key combo
to the known_host pool kept in memory if it wasn't already present there. The
adding of data to the file is done by completely replacing the file with a new
copy, so the permissions of the file must allow this.
.IP CURLKHSTAT_FINE
The host+key is accepted libcurl will continue with the connection. This will
also add the host+key combo to the known_host pool kept in memory if it wasn't
already present there.
.IP CURLKHSTAT_REJECT
The host+key is rejected. libcurl will deny the connection to continue and it
will be closed.
.IP CURLKHSTAT_DEFER
The host+key is rejected, but the SSH connection is asked to be kept alive.
This feature could be used when the app wants to somehow return back and act
on the host+key situation and then retry without needing the overhead of
setting it up from scratch again.
.RE
 (Added in 7.19.6)
.IP CURLOPT_SSH_KEYDATA
Pass a void * as parameter. This pointer will be passed along verbatim to the
callback set with \fICURLOPT_SSH_KEYFUNCTION\fP. (Added in 7.19.6)
.SH OTHER OPTIONS
.IP CURLOPT_PRIVATE
Pass a void * as parameter, pointing to data that should be associated with
this curl handle.  The pointer can subsequently be retrieved using
\fIcurl_easy_getinfo(3)\fP with the CURLINFO_PRIVATE option. libcurl itself
does nothing with this data. (Added in 7.10.3)
.IP CURLOPT_SHARE
Pass a share handle as a parameter. The share handle must have been created by
a previous call to \fIcurl_share_init(3)\fP. Setting this option, will make
this curl handle use the data from the shared handle instead of keeping the
data to itself. This enables several curl handles to share data. If the curl
handles are used simultaneously in multiple threads, you \fBMUST\fP use the
locking methods in the share handle. See \fIcurl_share_setopt(3)\fP for
details.

If you add a share that is set to share cookies, your easy handle will use
that cookie cache and get the cookie engine enabled. If you unshare an object
that was using cookies (or change to another object that doesn't share
cookies), the easy handle will get its cookie engine disabled.

Data that the share object is not set to share will be dealt with the usual
way, as if no share was used.
.IP CURLOPT_NEW_FILE_PERMS
Pass a long as a parameter, containing the value of the permissions that will
be assigned to newly created files on the remote server.  The default value is
\fI0644\fP, but any valid value can be used.  The only protocols that can use
this are \fIsftp://\fP, \fIscp://\fP, and \fIfile://\fP. (Added in 7.16.4)
.IP CURLOPT_NEW_DIRECTORY_PERMS
Pass a long as a parameter, containing the value of the permissions that will
be assigned to newly created directories on the remote server.  The default
value is \fI0755\fP, but any valid value can be used.  The only protocols that
can use this are \fIsftp://\fP, \fIscp://\fP, and \fIfile://\fP.
(Added in 7.16.4)
.SH TELNET OPTIONS
.IP CURLOPT_TELNETOPTIONS
Provide a pointer to a curl_slist with variables to pass to the telnet
negotiations. The variables should be in the format <option=value>. libcurl
supports the options 'TTYPE', 'XDISPLOC' and 'NEW_ENV'. See the TELNET
standard for details.
.SH RETURN VALUE
CURLE_OK (zero) means that the option was set properly, non-zero means an
error occurred as \fI<curl/curl.h>\fP defines. See the \fIlibcurl-errors(3)\fP
man page for the full list with descriptions.

If you try to set an option that libcurl doesn't know about, perhaps because
the library is too old to support it or the option was removed in a recent
version, this function will return \fICURLE_FAILED_INIT\fP.
.SH "SEE ALSO"
.BR curl_easy_init "(3), " curl_easy_cleanup "(3), " curl_easy_reset "(3)"