Provided by: libcurl4-doc_7.81.0-1ubuntu1.20_all bug

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),