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 the following options duplicated from the parent: CURLOPT_WRITEFUNCTION(3), CURLOPT_WRITEDATA(3), CURLOPT_HEADERFUNCTION(3), CURLOPT_HEADERDATA(3), CURLOPT_DEBUGFUNCTION(3), CURLOPT_DEBUGDATA(3), CURLOPT_PROGRESSFUNCTION(3), CURLOPT_XFERINFOFUNCTION(3), CURLOPT_PROGRESSDATA(3) and CURLOPT_XFERINFODATA(3).

It is then up to the application to alter/set 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 functions 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 functions. 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 like for normal streams.

The header fields can also be accessed with curl_easy_header(3), introduced in later libcurl versions.

CALLBACK RETURN VALUE¶

CURL_PUSH_OK (0)

The application has accepted the stream and it can now start receiving 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 application, the easy handle is destroyed by libcurl.

CURL_PUSH_ERROROUT (2)

Returning this code rejects the pushed stream and returns an error 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-" */
static 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