111 lines
2.8 KiB
Markdown
111 lines
2.8 KiB
Markdown
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---
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c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
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SPDX-License-Identifier: curl
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Title: CURLOPT_TRAILERFUNCTION
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Section: 3
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Source: libcurl
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See-also:
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- CURLOPT_TRAILERDATA (3)
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- CURLOPT_WRITEFUNCTION (3)
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---
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# NAME
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CURLOPT_TRAILERFUNCTION - callback for sending trailing headers
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# SYNOPSIS
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~~~c
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#include <curl.h>
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int curl_trailer_callback(struct curl_slist ** list, void *userdata);
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CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERFUNCTION,
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curl_trailer_callback *func);
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~~~
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# DESCRIPTION
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Pass a pointer to a callback function.
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This callback function is called once right before sending the final CR LF in
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an HTTP chunked transfer to fill a list of trailing headers to be sent before
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finishing the HTTP transfer.
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You can set the userdata argument with the CURLOPT_TRAILERDATA(3)
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option.
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The trailing headers included in the linked list must not be CRLF-terminated,
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because libcurl adds the appropriate line termination characters after each
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header item.
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If you use curl_slist_append(3) to add trailing headers to the *curl_slist*
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then libcurl duplicates the strings, and frees the *curl_slist* once the
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trailers have been sent.
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If one of the trailing header fields is not formatted correctly it is ignored
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and an info message is emitted.
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The return value can either be **CURL_TRAILERFUNC_OK** or
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**CURL_TRAILERFUNC_ABORT** which would respectively instruct libcurl to
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either continue with sending the trailers or to abort the request.
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If you set this option to NULL, then the transfer proceeds as usual
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without any interruptions.
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# DEFAULT
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NULL
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# PROTOCOLS
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HTTP
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# EXAMPLE
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~~~c
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static int trailer_cb(struct curl_slist **tr, void *data)
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{
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/* libcurl frees the list */
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*tr = curl_slist_append(*tr, "My-super-awesome-trailer: trailer-stuff");
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return CURL_TRAILERFUNC_OK;
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}
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int main(void)
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{
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CURL *curl = curl_easy_init();
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if(curl) {
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CURLcode res;
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/* Set the URL of the request */
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curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
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/* Now set it as a put */
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curl_easy_setopt(curl, CURLOPT_PUT, 1L);
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/* Assuming we have a function that returns the data to be pushed
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Let that function be read_cb */
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curl_easy_setopt(curl, CURLOPT_READFUNCTION, trailer_cb);
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struct curl_slist *headers = NULL;
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headers = curl_slist_append(headers, "Trailer: My-super-awesome-trailer");
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res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
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/* Set the trailers filling callback */
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curl_easy_setopt(curl, CURLOPT_TRAILERFUNCTION, trailer_cb);
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/* Perform the transfer */
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res = curl_easy_perform(curl);
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curl_easy_cleanup(curl);
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curl_slist_free_all(headers);
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}
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}
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~~~
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# AVAILABILITY
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This option was added in curl 7.64.0 and is present if HTTP support is enabled.
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# RETURN VALUE
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Returns CURLE_OK.
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