Ubuntu Manpage: CURLOPT_HTTPHEADER

Provided by: libcurl4-doc_8.5.0-2ubuntu10.6_all

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.