mirror of
https://github.com/moparisthebest/curl
synced 2024-12-25 01:28:51 -05:00
9526cbe6bc
For compatibility with `fwrite`, the `CURLOPT_WRITEFUNCTION` callback is passed two `size_t` parameters which, when multiplied, designate the number of bytes of data passed in. In practice, CURL always sets the first parameter (`size`) to 1. This practice is also enshrined in documentation and cannot be changed in future. The documentation states that the default callback is `fwrite`, which means `fwrite` must be a suitable function for this purpose. However, the documentation also states that the callback must return the number of *bytes* it successfully handled, whereas ISO C `fwrite` returns the number of items (each of size `size`) which it wrote. The only way these numbers can be equal is if `size` is 1. Since `size` is 1 and can never be changed in future anyway, document that fact explicitly and let users rely on it. Closes #2787
82 lines
3.6 KiB
Groff
82 lines
3.6 KiB
Groff
.\" **************************************************************************
|
|
.\" * _ _ ____ _
|
|
.\" * Project ___| | | | _ \| |
|
|
.\" * / __| | | | |_) | |
|
|
.\" * | (__| |_| | _ <| |___
|
|
.\" * \___|\___/|_| \_\_____|
|
|
.\" *
|
|
.\" * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
|
|
.\" *
|
|
.\" * This software is licensed as described in the file COPYING, which
|
|
.\" * you should have received as part of this distribution. The terms
|
|
.\" * are also available at https://curl.haxx.se/docs/copyright.html.
|
|
.\" *
|
|
.\" * You may opt to use, copy, modify, merge, publish, distribute and/or sell
|
|
.\" * copies of the Software, and permit persons to whom the Software is
|
|
.\" * furnished to do so, under the terms of the COPYING file.
|
|
.\" *
|
|
.\" * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
|
|
.\" * KIND, either express or implied.
|
|
.\" *
|
|
.\" **************************************************************************
|
|
.\"
|
|
.TH CURLOPT_WRITEFUNCTION 3 "16 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
|
|
.SH NAME
|
|
CURLOPT_WRITEFUNCTION \- set callback for writing received data
|
|
.SH SYNOPSIS
|
|
.nf
|
|
#include <curl/curl.h>
|
|
|
|
size_t write_callback(char *ptr, size_t size, size_t nmemb, void *userdata);
|
|
|
|
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_WRITEFUNCTION, write_callback);
|
|
.SH DESCRIPTION
|
|
Pass a pointer to your callback function, which should match the prototype
|
|
shown above.
|
|
|
|
This callback function gets called by libcurl as soon as there is data
|
|
received that needs to be saved. \fIptr\fP points to the delivered data, and
|
|
the size of that data is \fInmemb\fP; \fIsize\fP is always 1.
|
|
|
|
The callback function will be passed as much data as possible in all invokes,
|
|
but you must not make any assumptions. It may be one byte, it may be
|
|
thousands. The maximum amount of body data that will be passed to the write
|
|
callback is defined in the curl.h header file: \fICURL_MAX_WRITE_SIZE\fP (the
|
|
usual default is 16K). If \fICURLOPT_HEADER(3)\fP is enabled, which makes
|
|
header data get passed 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.
|
|
|
|
This function may be called with zero bytes data if the transferred file is
|
|
empty.
|
|
|
|
The data passed to this function will not be zero terminated!
|
|
|
|
Set the \fIuserdata\fP argument with the \fICURLOPT_WRITEDATA(3)\fP option.
|
|
|
|
Your callback should return the number of bytes actually taken care of. If
|
|
that amount differs from the amount passed to your callback function, it'll
|
|
signal an error condition to the library. This will cause the transfer to get
|
|
aborted and the libcurl function used will return \fICURLE_WRITE_ERROR\fP.
|
|
|
|
If your callback function returns CURL_WRITEFUNC_PAUSE it will cause this
|
|
transfer to become paused. See \fIcurl_easy_pause(3)\fP for further details.
|
|
|
|
Set this option to NULL to get the internal default function used instead of
|
|
your callback. The internal default function will write the data to the FILE *
|
|
given with \fICURLOPT_WRITEDATA(3)\fP.
|
|
.SH DEFAULT
|
|
libcurl will use 'fwrite' as a callback by default.
|
|
.SH PROTOCOLS
|
|
For all protocols
|
|
.SH AVAILABILITY
|
|
Support for the CURL_WRITEFUNC_PAUSE return code was added in version 7.18.0.
|
|
.SH RETURN VALUE
|
|
This will return CURLE_OK.
|
|
.SH EXAMPLE
|
|
A common technique is to use this callback to store the incoming data into a
|
|
dynamically growing allocated buffer. Like in the getinmemory example:
|
|
https://curl.haxx.se/libcurl/c/getinmemory.html
|
|
.SH "SEE ALSO"
|
|
.BR CURLOPT_WRITEDATA "(3), " CURLOPT_READFUNCTION "(3), "
|