NAME

       CURLOPT_HTTPHEADER - set of HTTP headers

SYNOPSIS

       #include <curl/curl.h>

       CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPHEADER,
                                 struct curl_slist *headers);

DESCRIPTION

       Pass a pointer to a linked list of HTTP headers to pass to the server and/or proxy in your
       HTTP request. The same list can be used for both host and proxy requests!

       When used within an IMAP or SMTP request to upload a MIME  mail,  the  given  header  list
       establishes  the document-level MIME headers to prepend to the uploaded document described
       by CURLOPT_MIMEPOST(3). This does not affect raw mail uploads.

       The linked list should be a fully valid list of struct curl_slist structs properly  filled
       in.  Use curl_slist_append(3) to create the list and curl_slist_free_all(3) to clean up an
       entire list. If you add  a  header  that  is  otherwise  generated  and  used  by  libcurl
       internally,  your  added header is used instead. If you add a header with no content as in
       'Accept:' (no data on the right  side  of  the  colon),  the  internally  used  header  is
       disabled/removed.  With  this option you can add new headers, replace internal headers and
       remove internal headers. To add a header with no content (nothing to the right side of the
       colon), use the form 'name;' (note the ending semicolon).

       The  headers included in the linked list must not be CRLF-terminated, because libcurl adds
       CRLF after each header item itself. Failure to comply with this might  result  in  strange
       behavior.  libcurl passes on the verbatim strings you give it, without any filter or other
       safe guards. That includes white space and control characters.

       The first line in an HTTP request (containing the method, usually a GET or POST) is not  a
       header and cannot be replaced using this option. Only the lines following the request-line
       are headers. Adding this method line in this list of headers only causes your  request  to
       send an invalid header. Use CURLOPT_CUSTOMREQUEST(3) to change the method.

       When  this  option is passed to curl_easy_setopt(3), libcurl does not copy the entire list
       so you must keep it around until you no longer use this handle for a transfer  before  you
       call curl_slist_free_all(3) on the list.

       Pass a NULL to this option to reset back to no custom headers.

       The most commonly replaced HTTP headers have "shortcuts" in the options CURLOPT_COOKIE(3),
       CURLOPT_USERAGENT(3) and CURLOPT_REFERER(3). We recommend using those.

       There is an alternative option that sets or replaces headers only for  requests  that  are
       sent  with CONNECT to a proxy: CURLOPT_PROXYHEADER(3). Use CURLOPT_HEADEROPT(3) to control
       the behavior.

SPECIFIC HTTP HEADERS

       Setting some specific headers causes libcurl to act differently.

       Host:  The specified host name is used for cookie matching if the cookie  engine  is  also
              enabled for this transfer. If the request is done over HTTP/2 or HTTP/3, the custom
              host name is instead used in the ":authority" header field and Host: is not sent at
              all over the wire.

       Transfer-Encoding: chunked
              Tells  libcurl  the  upload  is  to  be done using this chunked encoding instead of
              providing the Content-Length: field in the request.

SPECIFIC MIME HEADERS

       When used to build a MIME e-mail for IMAP or SMTP, the  following  document-level  headers
       can be set to override libcurl-generated values:

       Mime-Version:
              Tells  the  parser  at  the  receiving  site how to interpret the MIME framing.  It
              defaults to "1.0" and should normally not be altered.

       Content-Type:
              Indicates the document's global structure type. By  default,  libcurl  sets  it  to
              "multipart/mixed",  describing  a  document  made of independent parts. When a MIME
              mail is only composed of alternative representations of the same data  (i.e.:  HTML
              and  plain text), this header must be set to "multipart/alternative".  In all cases
              the value must be of the form "multipart/*" to respect the document  structure  and
              may not include the "boundary=" parameter.

              Other  specific  headers  that do not have a libcurl default value but are strongly
              desired by mail delivery and user  agents  should  also  be  included.   These  are
              "From:", "To:", "Date:" and "Subject:" among others and their presence and value is
              generally checked by anti-spam utilities.

SECURITY CONCERNS

       By default, this option makes libcurl send the given headers in all HTTP requests done  by
       this  handle. You should therefore use this option with caution if you for example connect
       to the remote site using a proxy and a CONNECT request, you should  to  consider  if  that
       proxy  is  supposed to also get the headers. They may be private or otherwise sensitive to
       leak.

       Use CURLOPT_HEADEROPT(3) to make the headers only get sent to where you intend them to get
       sent.

       Custom headers are sent in all requests done by the easy handle, which implies that if you
       tell libcurl to follow redirects  (CURLOPT_FOLLOWLOCATION(3)),  the  same  set  of  custom
       headers  is  sent in the subsequent request. Redirects can of course go to other hosts and
       thus those servers get all the contents of your custom headers too.

       Starting in 7.58.0, libcurl specifically prevents "Authorization:" headers from being sent
       to  other  hosts  than  the  first  used  one,  unless  specifically  permitted  with  the
       CURLOPT_UNRESTRICTED_AUTH(3) option.

       Starting in 7.64.0, libcurl specifically prevents "Cookie:" headers  from  being  sent  to
       other   hosts   than   the   first  used  one,  unless  specifically  permitted  with  the
       CURLOPT_UNRESTRICTED_AUTH(3) option.

DEFAULT

       NULL

PROTOCOLS

       HTTP, IMAP and SMTP

EXAMPLE

       int main(void)
       {
         CURL *curl = curl_easy_init();

         struct curl_slist *list = NULL;

         if(curl) {
           curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

           list = curl_slist_append(list, "Shoesize: 10");
           list = curl_slist_append(list, "Accept:");

           curl_easy_setopt(curl, CURLOPT_HTTPHEADER, list);

           curl_easy_perform(curl);

           curl_slist_free_all(list); /* free the list */
         }
       }

AVAILABILITY

       As long as HTTP is enabled. Use in MIME mail added in 7.56.0.

RETURN VALUE

       Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.

SEE ALSO

       curl_mime_init(3),  CURLOPT_CUSTOMREQUEST(3),   CURLOPT_HEADER(3),   CURLOPT_HEADEROPT(3),
       CURLOPT_MIMEPOST(3), CURLOPT_PROXYHEADER(3)