mirror of
https://github.com/moparisthebest/curl
synced 2024-11-17 06:55:02 -05:00
97934a2f71
For compatibility with `fwrite`, the `CURLOPT_HEADERFUNCTION` 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. Reported-by: Frank Gevaerts Commit-message-by: Christopher Head Ref: https://github.com/curl/curl/pull/2787 Fixes https://github.com/curl/curl/issues/4758
118 lines
5.1 KiB
Groff
118 lines
5.1 KiB
Groff
.\" **************************************************************************
|
|
.\" * _ _ ____ _
|
|
.\" * Project ___| | | | _ \| |
|
|
.\" * / __| | | | |_) | |
|
|
.\" * | (__| |_| | _ <| |___
|
|
.\" * \___|\___/|_| \_\_____|
|
|
.\" *
|
|
.\" * Copyright (C) 1998 - 2019, 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_HEADERFUNCTION 3 "17 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
|
|
.SH NAME
|
|
CURLOPT_HEADERFUNCTION \- callback that receives header data
|
|
.SH SYNOPSIS
|
|
#include <curl/curl.h>
|
|
|
|
size_t header_callback(char *buffer,
|
|
size_t size,
|
|
size_t nitems,
|
|
void *userdata);
|
|
|
|
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HEADERFUNCTION, header_callback);
|
|
.SH DESCRIPTION
|
|
Pass a pointer to your callback function, which should match the prototype
|
|
shown above.
|
|
|
|
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. \fIbuffer\fP points to the delivered data, and the size of
|
|
that data is \fInitems\fP; \fIsize\fP is always 1. Do not assume that the
|
|
header line is zero terminated!
|
|
|
|
The pointer named \fIuserdata\fP is the one you set with the
|
|
\fICURLOPT_HEADERDATA(3)\fP option.
|
|
|
|
This callback function must return the number of bytes actually taken care of.
|
|
If that amount differs from the amount passed in to your function, it'll signal
|
|
an error to the library. This will cause the transfer to get aborted and the
|
|
libcurl function in progress will return \fICURLE_WRITE_ERROR\fP.
|
|
|
|
A complete HTTP header that is passed to this function can be up to
|
|
\fICURL_MAX_HTTP_HEADER\fP (100K) bytes and includes the final line terminator.
|
|
|
|
If this option is not set, or if it is set to NULL, but
|
|
\fICURLOPT_HEADERDATA(3)\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(3)\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.
|
|
|
|
For an HTTP transfer, the status line and the blank line preceding the response
|
|
body are both included as headers and passed to this function.
|
|
|
|
When a server sends a chunked encoded transfer, it may contain a trailer. That
|
|
trailer is identical to an 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.
|
|
.SH LIMITATIONS
|
|
libcurl does not unfold HTTP "folded headers" (deprecated since RFC 7230). A
|
|
folded header is a header that continues on a subsequent line and starts with
|
|
a whitespace. Such folds will be passed to the header callback as a separate
|
|
one, although strictly it is just a continuation of the previous line.
|
|
.SH DEFAULT
|
|
Nothing.
|
|
.SH PROTOCOLS
|
|
Used for all protocols with headers or meta-data concept: HTTP, FTP, POP3,
|
|
IMAP, SMTP and more.
|
|
.SH EXAMPLE
|
|
.nf
|
|
static size_t header_callback(char *buffer, size_t size,
|
|
size_t nitems, void *userdata)
|
|
{
|
|
/* received header is nitems * size long in 'buffer' NOT ZERO TERMINATED */
|
|
/* 'userdata' is set with CURLOPT_HEADERDATA */
|
|
return nitems * size;
|
|
}
|
|
|
|
CURL *curl = curl_easy_init();
|
|
if(curl) {
|
|
curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");
|
|
|
|
curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_callback);
|
|
|
|
curl_easy_perform(curl);
|
|
}
|
|
.fi
|
|
.SH AVAILABILITY
|
|
Always
|
|
.SH RETURN VALUE
|
|
Returns CURLE_OK
|
|
.SH "SEE ALSO"
|
|
.BR CURLOPT_HEADERDATA "(3), " CURLOPT_WRITEFUNCTION "(3), "
|