133 lines
5.3 KiB
Groff
133 lines
5.3 KiB
Groff
.\" **************************************************************************
|
|
.\" * _ _ ____ _
|
|
.\" * Project ___| | | | _ \| |
|
|
.\" * / __| | | | |_) | |
|
|
.\" * | (__| |_| | _ <| |___
|
|
.\" * \___|\___/|_| \_\_____|
|
|
.\" *
|
|
.\" * Copyright (C) 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.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.
|
|
.\" *
|
|
.\" * SPDX-License-Identifier: curl
|
|
.\" *
|
|
.\" **************************************************************************
|
|
.\"
|
|
.TH CURLOPT_HEADERFUNCTION 3 "17 Jun 2014" libcurl libcurl
|
|
.SH NAME
|
|
CURLOPT_HEADERFUNCTION \- callback that receives header data
|
|
.SH SYNOPSIS
|
|
.nf
|
|
#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);
|
|
.fi
|
|
.SH DESCRIPTION
|
|
Pass a pointer to your callback function, which should match the prototype
|
|
shown above.
|
|
|
|
This callback function gets invoked by libcurl as soon as it has received
|
|
header data. The header callback is called once for each header and only
|
|
complete header lines are passed on to the callback. Parsing headers is easy
|
|
to do using this callback. \fIbuffer\fP points to the delivered data, and the
|
|
size of that data is \fInitems\fP; \fIsize\fP is always 1. The provide header
|
|
line is not null-terminated!
|
|
|
|
The pointer named \fIuserdata\fP is the one you set with the
|
|
\fICURLOPT_HEADERDATA(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
|
|
signals an error condition to the library. This causes the transfer to get
|
|
aborted and the libcurl function used returns \fICURLE_WRITE_ERROR\fP.
|
|
|
|
You can also abort the transfer by returning CURL_WRITEFUNC_ERROR. (7.87.0)
|
|
|
|
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 is used instead. That is 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 is 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 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 gets called
|
|
with the server responses to the commands that libcurl sends.
|
|
|
|
A more convenient way to get HTTP headers might be to use
|
|
\fIcurl_easy_header(3)\fP.
|
|
.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 are passed to the header callback as separate ones,
|
|
although strictly they are just continuations of the previous lines.
|
|
.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;
|
|
}
|
|
|
|
int main(void)
|
|
{
|
|
CURL *curl = curl_easy_init();
|
|
if(curl) {
|
|
curl_easy_setopt(curl, CURLOPT_URL, "https://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 curl_easy_header (3),
|
|
.BR CURLOPT_HEADERDATA (3),
|
|
.BR CURLOPT_WRITEFUNCTION (3)
|