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 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, "https://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-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 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

RETURN VALUE

       Returns CURLE_OK.

SEE ALSO

       CURLOPT_TRAILERDATA(3),