Ubuntu Manpage: CURLOPT_HTTPHEADER

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!

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 one will be 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 will get
disabled. 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 'MyHeader;' (note the ending semicolon).

The headers included in the linked list must not be CRLF-terminated, because libcurl adds
CRLF after each header item. Failure to comply with this will result in strange bugs
because the server will most likely ignore part of the headers you specified.

The first line in a 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 will only cause 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 will 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 headers have "shortcuts" in the options CURLOPT_COOKIE(3),
CURLOPT_USERAGENT(3) and CURLOPT_REFERER(3). We recommend using those.

There's 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 HEADERS

       Setting some specific headers will cause libcurl to act differently.

       Host:  The  specified  host  name will be 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  will instead be used in the ":authority" header field and Host:
              will not be 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.

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 handles, which  implies  that  if
       you  tell  libcurl to follow redirects (CURLOPT_FOLLOWLOCATION(3)), the same set of custom
       headers will be sent in the subsequent request. Redirects can of course go to other  hosts
       and thus those servers will get all the contents of your custom headers too.

       Starting  in 7.58.0, libcurl will specifically prevent "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 will specifically prevent "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

EXAMPLE

       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

RETURN VALUE

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