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+= nng_http_req_add_header(3)
+:doctype: manpage
+:manmanual: nng
+:mansource: nng
+:manvolnum: 3
+:copyright: Copyright 2018 Staysail Systems, Inc. <info@staysail.tech> \
+            Copyright 2018 Capitar IT Group BV <info@capitar.com> \
+            This software 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_req_add_header - add HTTP request header
+
+== SYNOPSIS
+
+[source, c]
+-----------
+#include <nng/nng.h>
+
+int nng_http_req_add_header(nng_http_req *req, const char *key,
+    const char *val);
+-----------
+
+== DESCRIPTION
+
+The `nng_http_req_add_header()` adds an HTTP header for the request
+_req_ 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 <<nng_http_req_set_header#,nng_http_req_set_header(3)>> 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
+
+`NNG_ENOMEM`:: Insufficient memory to perform the operation.
+`NNG_ENOTSUP`:: No support for HTTP in the library.
+
+== SEE ALSO
+
+<<nng_http_req_alloc#,nng_http_req_alloc(3)>>,
+<<nng_http_req_del_header#,nng_http_req_del_header(3)>>,
+<<nng_http_req_get_header#,nng_http_req_get_header(3)>>,
+<<nng_http_req_set_header#,nng_http_req_set_header(3)>>,
+<<nng#,nng(7)>>
+
+== COPYRIGHT
+
+Copyright 2018 mailto:info@staysail.tech[Staysail Systems, Inc.] +
+Copyright 2018 mailto:info@capitar.com[Capitar IT Group BV]
+
+This document is supplied under the terms of the
+https://opensource.org/licenses/MIT[MIT License].