plucky (3) CURLOPT_TRAILERFUNCTION.3.gz

NAME

       CURLOPT_TRAILERFUNCTION - callback for sending trailing headers

SYNOPSIS

       #include <curl.h>

       int curl_trailer_callback(struct curl_slist ** list, void *userdata);

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERFUNCTION,
                                 curl_trailer_callback *func);

DESCRIPTION

       Pass a pointer to a callback function.

       This callback function is called once right before sending the final CR LF in an HTTP chunked transfer to
       fill a list of trailing headers to be sent before finishing the HTTP transfer.

       You can set the userdata argument with the CURLOPT_TRAILERDATA(3) option.

       The trailing headers included in the linked list must not be CRLF-terminated, because  libcurl  adds  the
       appropriate line termination characters after each header item.

       If  you  use  curl_slist_append(3)  to add trailing headers to the curl_slist then libcurl duplicates the
       strings, and frees the curl_slist once the trailers have been sent.

       If one of the trailing header fields is not formatted correctly it is ignored  and  an  info  message  is
       emitted.

       The  return  value  can  either be CURL_TRAILERFUNC_OK or CURL_TRAILERFUNC_ABORT which would respectively
       instruct libcurl to either continue with sending the trailers or to abort the request.

       If you set this option to NULL, then the transfer proceeds as usual without any interruptions.

DEFAULT

       NULL

PROTOCOLS

       This functionality affects http only

EXAMPLE

       static int trailer_cb(struct curl_slist **tr, void *data)
       {
         /* libcurl frees the list */
         *tr = curl_slist_append(*tr, "My-super-awesome-trailer: trailer-stuff");
         return CURL_TRAILERFUNC_OK;
       }

       int main(void)
       {
         CURL *curl = curl_easy_init();
         if(curl) {
           CURLcode res;

           /* Set the URL of the request */
           curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
           /* Now set it as a put */
           curl_easy_setopt(curl, CURLOPT_UPLOAD, 1L);

           /* Assuming we have a function that returns the data to be pushed
              Let that function be read_cb */
           curl_easy_setopt(curl, CURLOPT_READFUNCTION, trailer_cb);

           struct curl_slist *headers = NULL;
           headers = curl_slist_append(headers, "Trailer: My-super-awesome-trailer");
           res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);

           /* Set the trailers filling callback */
           curl_easy_setopt(curl, CURLOPT_TRAILERFUNCTION, trailer_cb);

           /* Perform the transfer */
           res = curl_easy_perform(curl);

           curl_easy_cleanup(curl);

           curl_slist_free_all(headers);
         }
       }

AVAILABILITY

       Added in curl 7.64.0

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_TRAILERDATA(3), CURLOPT_WRITEFUNCTION(3)