curl/docs/libcurl/opts/CURLOPT_HTTPHEADER.3

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.TH CURLOPT_HTTPHEADER 3 "17 Jun 2014" "libcurl 7.37.0" "curl_easy_setopt options"
.SH NAME
CURLOPT_HTTPHEADER \- set of HTTP headers
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HTTPHEADER,
                          struct curl_slist *headers);
.fi
.SH 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 \fBstruct curl_slist\fP
structs properly filled in. Use \fIcurl_slist_append(3)\fP to create the list
and \fIcurl_slist_free_all(3)\fP 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 \fBmust not\fP 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
\fICURLOPT_CUSTOMREQUEST(3)\fP to change the method.

When this option is passed to \fIcurl_easy_setopt(3)\fP, libcurl will not copy
the entire list so you \fBmust\fP keep it around until you no longer use this
\fIhandle\fP for a transfer before you call \fIcurl_slist_free_all(3)\fP 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
\fICURLOPT_COOKIE(3)\fP, \fICURLOPT_USERAGENT(3)\fP and
\fICURLOPT_REFERER(3)\fP. 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: \fICURLOPT_PROXYHEADER(3)\fP. Use
\fICURLOPT_HEADEROPT(3)\fP to control the behavior.
.SH SPECIFIC HEADERS
Setting some specific headers will cause libcurl to act differently.
.IP "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.
.IP "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.
.SH 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 \fICURLOPT_HEADEROPT(3)\fP 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
(\fICURLOPT_FOLLOWLOCATION(3)\fP), 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 \fICURLOPT_UNRESTRICTED_AUTH(3)\fP 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 \fICURLOPT_UNRESTRICTED_AUTH(3)\fP option.
.SH DEFAULT
NULL
.SH PROTOCOLS
HTTP
.SH EXAMPLE
.nf
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 again */
}
.fi

.SH AVAILABILITY
As long as HTTP is enabled
.SH RETURN VALUE
Returns CURLE_OK if HTTP is supported, and CURLE_UNKNOWN_OPTION if not.
.SH "SEE ALSO"
.BR CURLOPT_CUSTOMREQUEST "(3), " CURLOPT_HEADEROPT "(3), "
.BR CURLOPT_PROXYHEADER "(3), " CURLOPT_HEADER "(3)"