78 lines
3.4 KiB
Groff
78 lines
3.4 KiB
Groff
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.\" **************************************************************************
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.\" * _ _ ____ _
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.\" * Project ___| | | | _ \| |
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.\" * / __| | | | |_) | |
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.\" * | (__| |_| | _ <| |___
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.\" * \___|\___/|_| \_\_____|
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.\" *
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.\" * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
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.\" *
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.\" * This software is licensed as described in the file COPYING, which
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.\" * you should have received as part of this distribution. The terms
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.\" * are also available at http://curl.haxx.se/docs/copyright.html.
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.\" *
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.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
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.\" * copies of the Software, and permit persons to whom the Software is
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.\" * furnished to do so, under the terms of the COPYING file.
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.\" *
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.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
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.\" * KIND, either express or implied.
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.\" *
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.\" **************************************************************************
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.\"
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.TH CURLOPT_WRITEFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
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.SH NAME
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CURLOPT_WRITEFUNCTION \- set callback for writing received data
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.SH SYNOPSIS
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.nf
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#include <curl/curl.h>
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size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);
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.SH DESCRIPTION
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Pass a pointer to your callback function, as the prototype shows above.
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This callback function gets called by libcurl as soon as there is data
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received that needs to be saved. \fIptr\fP points to the delivered data, and
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the size of that data is \fIsize\fP multiplied with \fInmemb\fP.
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The received data will not be zero terminated!
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Return the number of bytes actually taken care of. If that amount differs from
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the amount passed to your callback function, it'll signal an error condition
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to the library. This will cause the transfer to get aborted and return
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\fICURLE_WRITE_ERROR\fP.
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The callback function can return CURL_WRITEFUNC_PAUSE which then will cause
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writing to this connection to become paused. See \fIcurl_easy_pause(3)\fP for
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further details.
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This function may be called with zero bytes data if the transferred file is
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empty.
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Set this option to NULL to get the internal default function used instead of
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your callback. The internal default function will write the data to the FILE *
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given with \fICURLOPT_WRITEDATA(3)\fP.
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Set the \fIuserdata\fP argument with the \fICURLOPT_WRITEDATA(3)\fP option.
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The callback function will be passed as much data as possible in all invokes,
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but you cannot possibly make any assumptions. It may be one byte, it may be
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thousands. The maximum amount of body data that can be passed to the write
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callback is defined in the curl.h header file: CURL_MAX_WRITE_SIZE (the usual
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default is 16K). If you however have \fICURLOPT_HEADER(3)\fP set, which sends
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header data to the write callback, you can get up to
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\fICURL_MAX_HTTP_HEADER\fP bytes of header data passed into it. This usually
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means 100K.
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.SH PROTOCOLS
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For all protocols
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.SH AVAILABILITY
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Support for the CURL_WRITEFUNC_PAUSE return code was added in version 7.18.0.
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.SH EXAMPLE
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A common technique is to use this callback to store the incoming data into a
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dynamically growing allocated buffer. Like in the getinmemory example:
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http://curl.haxx.se/libcurl/c/getinmemory.html
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.SH "SEE ALSO"
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.BR CURLOPT_WRITEDATA "(3), " CURLOPT_READFUNCTION "(3), "
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