Provided by: libcurl4-doc_7.58.0-2ubuntu3.24_all bug


       CURLMOPT_PUSHFUNCTION - callback that approves or denies server pushes


       #include <curl/curl.h>

       char *curl_pushheader_bynum(struct curl_pushheaders *h, size_t num);
       char *curl_pushheader_byname(struct curl_pushheaders *h, const char *name);

       int curl_push_callback(CURL *parent,
                              CURL *easy,
                              size_t num_headers,
                              struct curl_pushheaders *headers,
                              void *userp);

       CURLMcode curl_multi_setopt(CURLM *handle, CURLMOPT_PUSHFUNCTION,
                                   curl_push_callback func);


       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  will  be  denied


       The callback gets its arguments like this:

       parent  is  the  handle  of the stream on which this push arrives. The new handle has been
       duphandle()d 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 functions described
       below. This only accesses and provides  the  PUSH_PROMISE  headers,  the  normal  response
       headers will be provided in the header callback as usual.

       userp is the pointer set with CURLMOPT_PUSHDATA(3)

       If the callback returns CURL_PUSH_OK, the 'easy' handle will be 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. The normal response headers will be passed to  the  header  callback  for  pushed
       streams just as for normal streams.

              Returns  the  header  at  index  'num'  (or NULL). The returned pointer points to a
              "name:value" string that will be freed when this callback returns.

              Returns the value for the given header name (or NULL). This is a shortcut  so  that
              the  application  doesn't  have  to  loop through all headers to find the one it is
              interested in. The data pointed will be freed when this callback returns.  If  more
              than one header field use the same name, this returns only the first one.


       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 for this will reach the application, the
              easy handle will be destroyed by libcurl.

       *      All other return codes are reserved for future use.


       NULL, no callback


       HTTP(S) (HTTP/2 only)


       /* only allow pushes for file names starting with "push-" */
       int push_callback(CURL *parent,
                         CURL *easy,
                         size_t num_headers,
                         struct curl_pushheaders *headers,
                         void *userp)
         char *headp;
         int *transfers = (int *)userp;
         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;

       curl_multi_setopt(multi, CURLMOPT_PUSHFUNCTION, push_callback);
       curl_multi_setopt(multi, CURLMOPT_PUSHDATA, &counter);


       Added in 7.44.0


       Returns CURLM_OK if the option is supported, and CURLM_UNKNOWN_OPTION if not.