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                     23: .TH CURLOPT_TRAILERFUNCTION 3 "October 31, 2019" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_TRAILERFUNCTION \- Set callback for sending trailing headers
                     27: .SH SYNOPSIS
                     28: #include <curl.h>
                     29: 
                     30: int curl_trailer_callback(struct curl_slist ** list, void *userdata);
                     31: 
                     32: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERFUNCTION, curl_trailer_callback *func);
                     33: .SH DESCRIPTION
                     34: Pass a pointer to a callback function.
                     35: 
                     36: This callback function will be called once right before sending the final
                     37: CR LF in an HTTP chunked transfer to fill a list of trailing headers to be
                     38: sent before finishing the HTTP transfer.
                     39: 
                     40: You can set the userdata argument with the CURLOPT_TRAILERDATA option.
                     41: 
                     42: The trailing headers included in the linked list must not be CRLF-terminated,
                     43: because libcurl will add the appropriate line termination characters after
                     44: each header item.
                     45: 
                     46: If you use curl_slist_append to add trailing headers to the curl_slist then
                     47: libcurl will duplicate the strings, and will free the curl_slist and the
                     48: duplicates once the trailers have been sent.
                     49: 
                     50: If one of the trailing headers is not formatted correctly
                     51: (i.e. HeaderName: headerdata) it will be ignored and an info message
                     52: will be emitted.
                     53: 
                     54: The return value can either be CURL_TRAILERFUNC_OK or CURL_TRAILERFUNC_ABORT
                     55: which would respectively instruct libcurl to either continue with sending the
                     56: trailers or to abort the request.
                     57: 
                     58: If you set this option to NULL, then the transfer proceeds as usual
                     59: without any interruptions.
                     60: .SH DEFAULT
                     61: NULL
                     62: .SH PROTOCOLS
                     63: HTTP
                     64: .SH EXAMPLE
                     65: #include <curl/curl.h>
                     66: 
                     67: static int trailer_cb(struct curl_slist **tr, void *data)
                     68: {
                     69:   /* libcurl will free the list */
                     70:   tr = curl_slist_append(*tr, "My-super-awesome-trailer: trailer-stuff");
                     71:   return CURL_TRAILERFUNC_OK;
                     72: }
                     73: 
                     74: CURL *curl = curl_easy_init();
                     75: if(curl) {
                     76:   /* Set the URL of the request */
                     77:   curl_easy_setopt(curl, CURLOPT_URL, "http://example.com/");
                     78:   /* Now set it as a put */
                     79:   curl_easy_setopt(curl, CURLOPT_PUT, 1L);
                     80: 
                     81:   /* Assuming we have a function that will return the data to be pushed
                     82:      Let that function be read_cb */
                     83:   curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_cb);
                     84: 
                     85:   struct curl_slist *headers = NULL;
                     86:   headers = curl_slist_append(headers, "Trailer: My-super-awsome-trailer");
                     87:   res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
                     88: 
                     89:   /* Set the trailers filling callback */
                     90:   curl_easy_setopt(curl, CURLOPT_TRAILERFUNCTION, trailer_cb);
                     91: 
                     92:   /* Perform the request, res will get the return code */
                     93:   res = curl_easy_perform(curl);
                     94: 
                     95:   curl_easy_cleanup(curl);
                     96: 
                     97:   curl_slist_free_all(headers);
                     98: }
                     99: .SH AVAILABILITY
                    100: This option was added in curl 7.64.0 and is present if HTTP support is enabled
                    101: .SH "SEE ALSO"
                    102: .BR CURLOPT_TRAILERDATA "(3), "