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CURLOPT_HTTPHEADER(3)      Library Functions Manual      CURLOPT_HTTPHEADER(3)


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 hostname 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 hostname 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 email 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

       This functionality affects 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 */
         }
       }


HISTORY

       Use for MIME mail added in 7.56.0.


AVAILABILITY

       Added in curl 7.1


RETURN VALUE

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


SEE ALSO

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

libcurl                           2024-08-05             CURLOPT_HTTPHEADER(3)

curl 8.9.1 - Generated Tue Aug 6 18:03:40 CDT 2024
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