CURLOPT_HEADERFUNCTION(3)

CURLOPT_HEADERFUNCTION(3curl_easy_setopt optionCURLOPT_HEADERFUNCTION(3)

NAME

     CURLOPT_HEADERFUNCTION - callback that receives header data

SYNOPSIS

     #include <curl/curl.h>

     size_t header_callback(char *buffer,
                            size_t size,
                            size_t nitems,
                            void *userdata);

     CURLcode           curl_easy_setopt(CURL            *handle,
     CURLOPT_HEADERFUNCTION, header_callback);

DESCRIPTION

     Pass a pointer to your callback function, which should match
     the prototype shown above.

     This function gets called by  libcurl  as  soon  as  it  has
     received  header  data.  The  header callback will be called
     once for each header and  only  complete  header  lines  are
     passed  on  to  the  callback.  Parsing headers is very easy
     using this. The size of the data pointed  to  by  buffer  is
     size  multiplied  with  nmemb. Do not assume that the header
     line is zero terminated! The pointer named userdata  is  the
     one  you  set  with  the  CURLOPT_HEADERDATA(3) option. This
     callback function must return the number of  bytes  actually
     taken care of. If that amount differs from the amount passed
     in to your function, it'll signal an error to  the  library.
     This  will cause the transfer to get aborted and the libcurl
     function in progress will return CURLE_WRITE_ERROR.

     A complete HTTP header that is passed to this  function  can
     be up to CURL_MAX_HTTP_HEADER (100K) bytes.

     If this option is not set, or if it  is  set  to  NULL,  but
     CURLOPT_HEADERDATA(3) is set to anything but NULL, the func-
     tion used to accept response data will be used instead. That
     is,    it    will    be    the   function   specified   with
     CURLOPT_WRITEFUNCTION(3), or if it is not specified or  NULL
     - the default, stream-writing function.

     It's important to note that the callback will be invoked for
     the  headers  of  all  responses received after initiating a
     request and not just the final response. This  includes  all
     responses  which occur during authentication negotiation. If
     you need to operate on  only  the  headers  from  the  final
     response,  you  will need to collect headers in the callback
     yourself and use HTTP status lines, for example, to  delimit
     response boundaries.

     When a server sends  a  chunked  encoded  transfer,  it  may

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CURLOPT_HEADERFUNCTION(3curl_easy_setopt optionCURLOPT_HEADERFUNCTION(3)

     contain  a  trailer.  That  trailer  is  identical to a HTTP
     header and if such a trailer is received it is passed to the
     application  using  this callback as well. There are several
     ways to detect it  being  a  trailer  and  not  an  ordinary
     header:  1)  it  comes  after the response-body. 2) it comes
     after the final header line (CR LF) 3)  a  Trailer:   header
     among the regular response-headers mention what header(s) to
     expect in the trailer.

     For non-HTTP protocols like FTP, POP3, IMAP  and  SMTP  this
     function  will  get  called with the server responses to the
     commands that libcurl sends.

DEFAULT

     Nothing.

PROTOCOLS

     Used for all protocols with headers  or  meta-data  concept:
     HTTP, FTP, POP3, IMAP, SMTP and more.

EXAMPLE

     static size_t header_callback(char *buffer, size_t size,
                                   size_t nitems, void *userdata)
     {
       /* received header is nitems * size long in 'buffer' NOT ZERO TERMINATED */
       /* 'userdata' is set with CURLOPT_HEADERDATA */
       return nitems * size;
     }

     CURL *curl = curl_easy_init();
     if(curl) {
       curl_easy_setopt(curl, CURLOPT_URL, "http://example.com");

       curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, header_callback);

       curl_easy_perform(curl);
     }

AVAILABILITY

     Always

RETURN VALUE

     Returns CURLE_OK

SEE ALSO

     CURLOPT_HEADERDATA(3), CURLOPT_WRITEFUNCTION(3),

libcurl 7.58.0   Last change: February 03, 2016                 2