CURLMOPT_PUSHFUNCTION(3) Library Functions Manual CURLMOPT_PUSHFUNCTION(3)
NAME
CURLMOPT_PUSHFUNCTION - callback that approves or denies server pushes
SYNOPSIS
#include <curl/curl.h>
int curl_push_callback(CURL *parent,
CURL *easy,
size_t num_headers,
struct curl_pushheaders *headers,
void *clientp);
CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_PUSHFUNCTION,
curl_push_callback func);
DESCRIPTION
This callback gets called when a new HTTP/2 stream is being pushed by
the server (using the PUSH_PROMISE frame). If no push callback is set,
all offered pushes are denied automatically.
CALLBACK DESCRIPTION
The callback gets its arguments like this:
parent is the handle of the stream on which this push arrives. The new
handle has been duplicated from the parent, meaning that it has gotten
all its options inherited. It is then up to the application to alter any
options if desired.
easy is a newly created handle that represents this upcoming transfer.
num_headers is the number of name+value pairs that was received and can
be accessed
headers is a handle used to access push headers using the accessor func-
tions described below. This only accesses and provides the PUSH_PROMISE
headers, the normal response headers are provided in the header callback
as usual.
clientp is the pointer set with CURLMOPT_PUSHDATA(3)
If the callback returns CURL_PUSH_OK, the new easy handle is added to
the multi handle, the callback must not do that by itself.
The callback can access PUSH_PROMISE headers with two accessor func-
tions. These functions can only be used from within this callback and
they can only access the PUSH_PROMISE headers: curl_pushheader_byname(3)
and curl_pushheader_bynum(3). The normal response headers are passed to
the header callback for pushed streams just as for normal streams.
The header fields can also be accessed with curl_easy_header(3), intro-
duced in later libcurl versions.
CALLBACK RETURN VALUE
CURL_PUSH_OK (0)
The application has accepted the stream and it can now start re-
ceiving data, the ownership of the curl handle has been taken
over by the application.
CURL_PUSH_DENY (1)
The callback denies the stream and no data reaches the applica-
tion, the easy handle is destroyed by libcurl.
CURL_PUSH_ERROROUT (2)
Returning this code rejects the pushed stream and returns an er-
ror back on the parent stream making it get closed with an error.
(Added in 7.72.0)
* All other return codes are reserved for future use.
DEFAULT
NULL, no callback
PROTOCOLS
This functionality affects http only
EXAMPLE
#include <string.h>
/* only allow pushes for filenames starting with "push-" */
int push_callback(CURL *parent,
CURL *easy,
size_t num_headers,
struct curl_pushheaders *headers,
void *clientp)
{
char *headp;
int *transfers = (int *)clientp;
FILE *out;
headp = curl_pushheader_byname(headers, ":path");
if(headp && !strncmp(headp, "/push-", 6)) {
fprintf(stderr, "The PATH is %s\n", headp);
/* save the push here */
out = fopen("pushed-stream", "wb");
/* write to this file */
curl_easy_setopt(easy, CURLOPT_WRITEDATA, out);
(*transfers)++; /* one more */
return CURL_PUSH_OK;
}
return CURL_PUSH_DENY;
}
int main(void)
{
int counter;
CURLM *multi = curl_multi_init();
curl_multi_setopt(multi, CURLMOPT_PUSHFUNCTION, push_callback);
curl_multi_setopt(multi, CURLMOPT_PUSHDATA, &counter);
}
AVAILABILITY
Added in curl 7.44.0
RETURN VALUE
curl_multi_setopt(3) returns a CURLMcode indicating success or error.
CURLM_OK (0) means everything was OK, non-zero means an error occurred,
see libcurl-errors(3).
SEE ALSO
CURLMOPT_PIPELINING(3), CURLMOPT_PUSHDATA(3), CURLOPT_PIPEWAIT(3),
RFC7540
libcurl 2026-07-12 CURLMOPT_PUSHFUNCTION(3)
Generated by dwww version 1.16 on Sat Oct 3 05:56:31 CEST 2026.