227 lines
9.3 KiB
Plaintext
227 lines
9.3 KiB
Plaintext
_ _ ____ _
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/ __| | | | |_) | |
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| (__| |_| | _ <| |___
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\___|\___/|_| \_\_____|
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FAQ
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1. Problems connecting to SSL servers.
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It took a very long time before I could sort out why curl had problems
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to connect to certain SSL servers when using SSLeay or OpenSSL v0.9+.
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The error sometimes showed up similar to:
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16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233:
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It turned out to be because many older SSL servers don't deal with SSLv3
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requests properly. To correct this problem, tell curl to select SSLv2 from
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the command line (-2/--sslv2).
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I have also seen examples where the remote server didn't like the SSLv2
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request and instead you had to force curl to use SSLv3 with -3/--sslv3.
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2. curl: (1) SSL is disabled, https: not supported
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If you get this output when trying to get anything from a https:// server,
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it means that the configure script couldn't find all libs and include files
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it requires for SSL to work. If the configure script fails to find them,
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curl is simply built without SSL support.
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To get the https:// support into a curl that was previously built but that
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reports that https:// is not supported, you should dig through the document
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and logs and check out why the configure script doesn't find the SSL libs
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and/or include files.
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Also, check out the other paragraph in this FAQ labeled "configure doesn't
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find OpenSSL even when it is installed".
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3. Does curl support resume?
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Yes. Both ways on FTP, download ways on HTTP.
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Try the -c and -C options.
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4. Is libcurl thread safe?
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As version seven is slowly marching in as the libcurl version to use, we
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have made a serious attempt to address all places in the code where we could
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forsee problems for multi-threaded programs. If your system has them, curl
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will attempt to use threadsafe functions instead of non-safe ones.
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I am very interested in once and for all getting some kind of report or
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README file from those who have used libcurl in a threaded environment,
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since I haven't and I get this question more and more frequently!
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5. Why doesn't my posting using -F work?
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You can't simply use -F or -d at your choice. The web server that will
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receive your post assumes one of the formats. If the form you're trying to
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"fake" sets the type to 'multipart/form-data', than and only then you must
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use the -F type. In all the most common cases, you should use -d which then
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causes a posting with the type 'application/x-www-form-urlencoded'.
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I have described this in some detail in the README.curl file, and if you
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don't understand it the first time, read it again before you post questions
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about this to the mailing list. I would also suggest that you read through
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the mailing list archives for old postings and questions regarding this.
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6. Does curl support custom FTP commands?
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Yes it does, you can tell curl to perform optional commands both before
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and/or after a file transfer. Study the -Q/--quote option.
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Since curl is used for file transfers, you don't use curl to just perform
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ftp commands without transfering anything. Therefore you must always specify
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a URL to transfer to/from even when doing custom FTP commands.
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7. Does curl work with other SSL libraries?
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Curl has been written to use OpenSSL, although I doubt there would be much
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problems using a different library. I just don't know any other free one and
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that has limited my possibilities to develop against anything else.
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If anyone does "port" curl to use a commercial SSL library, I am of course
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very interested in getting the patch!
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8. configure doesn't find OpenSSL even when it is installed
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This may be because of several reasons.
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8.1. native linker doesn't find openssl
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Platforms: Solaris (native cc compiler) and HPUX (native cc compiler)
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When configuring curl, I specify --with-ssl. OpenSSL is installed in
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/usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find
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CRYPTO_lock in -lcrypto
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Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER
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-lcrypto, so ld can't find the library. This is due to a bug in the GNU
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autoconf tool.
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Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of
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./configure places the -L/usr/local/ssl/lib early enough in the command
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line to make things work
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Submitted by: Bob Allison <allisonb@users.sourceforge.net>
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8.2. only the libssl lib is missing
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If all include files and the libcrypto lib is present, with only the
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libssl being missing according to configure, this is mostly likely because
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a few functions are left out from the libssl.
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If the function names missing include RSA or RSAREF you can be certain
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that this is because libssl requires the RSA and RSASEF libs to build.
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See the INSTALL file section that explains how to add those libs to
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configure. Make sure that you remove the config.cache file before you
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rerun configure with the new flags.
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9. Why do I get problems when I use & in the URL?
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In general unix shells, the & letter is treated special and when used it
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runs the specified command in the background. To safely send the & as a
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part of a URL, you should qoute the entire URL by using single (') or
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double (") quotes around it.
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An example that would invoke a remote CGI that uses &-letters could be:
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curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl'
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10. How can I use {, }, [ or ] to specify multiple URLs?
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Because those letters have a special meaning to the shell, and to be used
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in a URL specified to curl you must quote them.
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An example that downloads two URLs (sequentially) would do:
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curl '{curl,www}.haxx.se'
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11. Where can I find a copy of LIBEAY32.DLL?
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That is an OpenSSL binary built for Windows.
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Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs
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on a windows machine to do https://. Check out the curl web page to find
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accurate and up-to-date pointers to recent OpenSSL DDLs and other binary
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packages.
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12. Why do I get downloaded data even though the web page doesn't exist?
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Curl asks remote servers for the page you specify. If the page doesn't
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exist at the server, the HTTP protocol defines how the server should
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respond and that means that headers and a "page" will be returned. That's
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simply how HTTP works.
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By using the --fail option you can tell curl explicitly to not get any data
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if the HTTP return code doesn't say success.
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13. Why do I get "HTTP/1.1 403 Forbidden" from a http server?
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RFC2616 clearly explains this return code:
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10.4.4 403 Forbidden
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The server understood the request, but is refusing to fulfill it.
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Authorization will not help and the request SHOULD NOT be repeated.
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If the request method was not HEAD and the server wishes to make
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public why the request has not been fulfilled, it SHOULD describe the
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reason for the refusal in the entity. If the server does not wish to
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make this information available to the client, the status code 404
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(Not Found) can be used instead.
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14. How can I disable the Pragma: nocache header?
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You can change all internally generated headers by adding a replacement
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with the -H/--header option. By adding a header with empty contents you
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safelt disables the headers. Use -H "Pragma:" to disable that specific
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header.
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15. Can you tell me what error code 142 means?
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All error codes that are larger than the highest documented error code
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means that curl has existed due to a timeout. There is currentl no nice way
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for curl to abort from such a condition and that's why it gets this
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undocumented error. This is planned to change in a future release.
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16. How do I keep usernames and passwords secret in Curl command lines?
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I see this problem as two parts:
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The first part is to avoid having clear-text passwords in the command line
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so that they don't appear in 'ps' outputs and similar. That is easily
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avoided by using the "-K" option that tells curl to read parameters from a
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file or stdin to which you can pass the secret info.
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To keep the passwords in your account secret from the rest of the world is
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not a task that curl addresses. You could of course encrypt them somehow to
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at least hide them from being read by human eyes, but that is not what
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anyone would call security.
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17. Does curl support javascript, ASP, XML, XHTML or HTML version Y?
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To curl, all contents are alike. It doesn't matter how the page was
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generated. It may be ASP, PHP, perl, shell-script, SSI or plain
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HTML-files. There's no difference to curl and it doesn't even know what
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kind of language that generated the page.
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Javascript is slightly different since that is code embedded in the HTML
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that is sent for the client to interpret and curl has no javascript
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interpreter.
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18. Does cURL support Socks (RFC 1928) ?
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No. Nobody has wanted it that badly yet. I would appriciate patches that
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brings this functionality.
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19. Can I use curl to delete/rename a file through FTP?
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Yes. You specify custom ftp commands with -Q/--quote.
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One example would be to delete a file after you have downloaded it:
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curl -O ftp://download.com/coolfile -Q '-DELE coolfile'
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