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

       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK (0) means everything was OK, non-zero means an error occurred, see libcurl-errors(3).

SEE ALSO

       CURLOPT_NOPROGRESS(3), CURLOPT_XFERINFODATA(3)

libcurl                                            2025-03-05                        CURLOPT_XFERINFOFUNCTION(3)