NAME

       CURLOPT_TRAILERFUNCTION - Set 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 will be 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 option.

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

       If  you  use curl_slist_append to add trailing headers to the curl_slist then libcurl will
       duplicate the strings, and will free the curl_slist and the duplicates once  the  trailers
       have been sent.

       If one of the trailing headers is not formatted correctly (i.e. HeaderName: headerdata) it
       will be ignored and an info message will be 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

       HTTP

EXAMPLE

       #include <curl/curl.h>

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

       CURL *curl = curl_easy_init(); if(curl) {
         /* Set the URL of the request */
         curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/");
         /* Now set it as a put */
         curl_easy_setopt(curl, CURLOPT_PUT, 1L);

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

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

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

         /* Perform the request, res will get the return code */
         res = curl_easy_perform(curl);

         curl_easy_cleanup(curl);

         curl_slist_free_all(headers); }

AVAILABILITY

       This option was added in curl 7.64.0 and is present if HTTP support is enabled

SEE ALSO

       CURLOPT_TRAILERDATA(3),