= nng_http_res_add_header(3http)
//
// Copyright 2018 Staysail Systems, Inc. <info@staysail.tech>
// Copyright 2018 Capitar IT Group BV <info@capitar.com>
//
// This document is supplied under the terms of the MIT License, a
// copy of which should be located in the distribution where this
// file was obtained (LICENSE.txt).  A copy of the license may also be
// found online at https://opensource.org/licenses/MIT.
//

== NAME

nng_http_res_add_header - add HTTP response header

== SYNOPSIS

[source, c]
----
#include <nng/nng.h>
#include <nng/supplemental/http/http.h>

int nng_http_res_add_header(nng_http_res *res, const char *key,
    const char *val);
----

== DESCRIPTION

The `nng_http_res_add_header()` adds an HTTP header for the response
_res_ and the _key_ to the _val_.
The _key_ and _val_ are copied.

If a header with the value of _key_ already exists, then a comma
and whitespace separate are appended to it, followed by _val_.

If no such header already exists, then one is created with the value _val_.

TIP: The HTTP specification requires that duplicate headers be treated
identically to a single header with multiple comma-delimited values.

TIP: See xref:nng_http_res_set_header.3http.adoc[`nng_http_res_set_header()`] if
replacement of an existing header rather than appending to it is desired.

The value of _key_ is case insensitive, and should not include the final
colon in an HTTP header.  For example, specifying `Host` or `hOSt` are
equivalent, whereas the value `Host:` is not a legal header key.

== RETURN VALUES

This function returns 0 on success, and non-zero otherwise.

== ERRORS

[horizontal]
`NNG_ENOMEM`:: Insufficient memory to perform the operation.
`NNG_ENOTSUP`:: No support for HTTP in the library.

== SEE ALSO

[.text-left]
xref:nng_http_res_alloc.3http.adoc[nng_http_res_alloc(3http)],
xref:nng_http_res_del_header.3http.adoc[nng_http_res_del_header(3http)],
xref:nng_http_res_get_header.3http.adoc[nng_http_res_get_header(3http)],
xref:nng_http_res_set_header.3http.adoc[nng_http_res_set_header(3http)],
xref:nng.7.adoc[nng(7)]
