NAME

       CURLOPT_XFERINFOFUNCTION - progress meter callback

SYNOPSIS

       #include <curl/curl.h>

       int progress_callback(void *clientp,
                             curl_off_t dltotal,
                             curl_off_t dlnow,
                             curl_off_t ultotal,
                             curl_off_t ulnow);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_XFERINFOFUNCTION,
                                 progress_callback);

DESCRIPTION

       Pass a pointer to your callback function, which should match the prototype shown above.

       This  function  gets  called by libcurl instead of its internal equivalent with a frequent
       interval. While data is being transferred it  gets  called  frequently,  and  during  slow
       periods  like  when  nothing  is  being transferred it can slow down to about one call per
       second.

       clientp is the pointer set with CURLOPT_XFERINFODATA(3), it is not used by libcurl but  is
       only passed along from the application to the callback.

       The  callback  gets  told  how  much  data  libcurl  is  about to transfer and has already
       transferred, in number of bytes. dltotal is the total number of bytes libcurl  expects  to
       download  in this transfer. dlnow is the number of bytes downloaded so far. ultotal is the
       total number of bytes libcurl expects to upload in this transfer. ulnow is the  number  of
       bytes uploaded so far.

       Unknown/unused  argument  values  passed to the callback are set to zero (like if you only
       download data, the upload size remains 0). Many times the callback is called one  or  more
       times first, before it knows the data sizes so a program must be made to handle that.

       Return zero from the callback if everything is fine.

       Return   1   from   this   callback   to  make  libcurl  abort  the  transfer  and  return
       CURLE_ABORTED_BY_CALLBACK.

       If your callback function returns CURL_PROGRESSFUNC_CONTINUE it makes libcurl to  continue
       executing the default progress function.

       If  you transfer data with the multi interface, this function is not called during periods
       of idleness unless you call the appropriate libcurl function that performs transfers.

       CURLOPT_NOPROGRESS(3) must be set to 0 to make this function actually get called.

DEFAULT

       NULL - use the internal progress meter. That is rarely wanted by users.

PROTOCOLS

       This functionality affects all supported protocols

EXAMPLE

       struct progress {
         char *private;
         size_t size;
       };

       static size_t progress_callback(void *clientp,
                                       curl_off_t dltotal,
                                       curl_off_t dlnow,
                                       curl_off_t ultotal,
                                       curl_off_t ulnow)
       {
         struct progress *memory = clientp;
         printf("my ptr: %p\n", memory->private);

         /* use the values */

         return 0; /* all is good */
       }

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           struct progress data;

           /* pass struct to callback  */
           curl_easy_setopt(curl, CURLOPT_XFERINFODATA, &data);

           /* enable progress callback getting called */
           curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0L);

           curl_easy_setopt(curl, CURLOPT_XFERINFOFUNCTION, progress_callback);
         }
       }

AVAILABILITY

       Added in curl 7.32.0

RETURN VALUE

       Returns CURLE_OK.

SEE ALSO

       CURLOPT_NOPROGRESS(3), CURLOPT_XFERINFODATA(3)