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CURLOPT_TRAILERFUNCTION(3)                            Library Functions Manual


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)

libcurl                           2025-02-08        CURLOPT_TRAILERFUNCTION(3)

curl 8.12.0 - Generated Wed Feb 19 11:35:04 CST 2025
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