CURLOPT_TRAILERFUNCTION(3)

1CURLOPT_TRAILERFUNCTION(3)          libcurl         CURLOPT_TRAILERFUNCTION(3)
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NAME

6       CURLOPT_TRAILERFUNCTION - callback for sending trailing headers
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SYNOPSIS

9       #include <curl.h>
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11       int curl_trailer_callback(struct curl_slist ** list, void *userdata);
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13       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_TRAILERFUNCTION,
14                                 curl_trailer_callback *func);
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DESCRIPTION

17       Pass a pointer to a callback function.
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19       This callback function will be called once right before sending the fi‐
20       nal CR LF in an HTTP chunked transfer to fill a list of trailing  head‐
21       ers to be sent before finishing the HTTP transfer.
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23       You  can  set the userdata argument with the CURLOPT_TRAILERDATA(3) op‐
24       tion.
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26       The trailing headers included in the linked list must not be  CRLF-ter‐
27       minated,  because  libcurl  will  add  the appropriate line termination
28       characters after each header item.
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30       If you use curl_slist_append to add trailing headers to the  curl_slist
31       then  libcurl  will duplicate the strings, and will free the curl_slist
32       and the duplicates once the trailers have been sent.
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34       If one of the trailing header fields is not formatted correctly it will
35       be ignored and an info message will be emitted.
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37       The  return  value  can  either be CURL_TRAILERFUNC_OK or CURL_TRAILER‐
38       FUNC_ABORT which would respectively instruct libcurl to either continue
39       with sending the trailers or to abort the request.
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41       If  you  set  this  option to NULL, then the transfer proceeds as usual
42       without any interruptions.
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DEFAULT

45       NULL
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PROTOCOLS

48       HTTP
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EXAMPLE

51       #include <curl/curl.h>
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53       static int trailer_cb(struct curl_slist **tr, void *data) {
54         /* libcurl will free the list */
55         *tr  =  curl_slist_append(*tr,  "My-super-awesome-trailer:   trailer-
56       stuff");
57         return CURL_TRAILERFUNC_OK; }
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59       CURL *curl = curl_easy_init(); if(curl) {
60         /* Set the URL of the request */
61         curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
62         /* Now set it as a put */
63         curl_easy_setopt(curl, CURLOPT_PUT, 1L);
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65         /* Assuming we have a function that will return the data to be pushed
66            Let that function be read_cb */
67         curl_easy_setopt(curl, CURLOPT_READFUNCTION, read_cb);
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69         struct curl_slist *headers = NULL;
70         headers   =  curl_slist_append(headers,  "Trailer:  My-super-awesome-
71       trailer");
72         res = curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers);
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74         /* Set the trailers filling callback */
75         curl_easy_setopt(curl, CURLOPT_TRAILERFUNCTION, trailer_cb);
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77         /* Perform the request, res will get the return code */
78         res = curl_easy_perform(curl);
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80         curl_easy_cleanup(curl);
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82         curl_slist_free_all(headers); }
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AVAILABILITY

85       This option was added in curl 7.64.0 and is present if HTTP support  is
86       enabled
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RETURN VALUE

89       Returns CURLE_OK.
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