CURLOPT_HEADERFUNCTION(3) curl_easy_setopt options CURLOPT_HEADERFUNCTION(3)NAMECURLOPT_HEADERFUNCTION - callback that receives header data
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);
DESCRIPTION
Pass a pointer to your callback function, which should match the proto‐
type 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. The size of the data pointed to by buffer is size
multiplied with nmemb. Do not assume that the header line is zero ter‐
minated! The pointer named userdata is the one you set with the CUR‐
LOPT_HEADERDATA(3) option. This callback function must return the num‐
ber 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 CURLE_WRITE_ERROR.
A complete HTTP header that is passed to this function can be up to
CURL_MAX_HTTP_HEADER (100K) bytes.
If this option is not set, or if it is set to NULL, but CURLOPT_HEADER‐
DATA(3) 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 CURLOPT_WRITEFUNCTION(3), 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 head‐
ers 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 call‐
back yourself and use HTTP status lines, for example, to delimit
response boundaries.
When a server sends a chunked encoded transfer, it may contain a
trailer. That trailer is identical to a 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.
DEFAULT
Nothing.
PROTOCOLS
Used for all protocols with headers or meta-data concept: HTTP, FTP,
POP3, IMAP, SMTP and more.
EXAMPLE
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);
}
AVAILABILITY
Always
RETURN VALUE
Returns CURLE_OK
SEE ALSOCURLOPT_HEADERDATA(3), CURLOPT_WRITEFUNCTION(3),
libcurl 7.37.0 17 Jun 2014 CURLOPT_HEADERFUNCTION(3)
