Add functions for getting and setting response headers

doc/src/manual/cowboy_req.asciidoc

@@ -67,7 +67,10 @@ Request body:
 Response:
 
 * link:man:cowboy_req:set_resp_cookie(3)[cowboy_req:set_resp_cookie(3)] - Set a cookie
+* link:man:cowboy_req:resp_header(3)[cowboy_req:resp_header(3)] - Access the named HTTP header set for the response
+* link:man:cowboy_req:resp_headers(3)[cowboy_req:resp_headers(3)] - Access HTTP headers set for the response
 * link:man:cowboy_req:set_resp_header(3)[cowboy_req:set_resp_header(3)] - Set a response header
+* link:man:cowboy_req:set_resp_headers(3)[cowboy_req:set_resp_headers(3)] - Set several response headers
 * link:man:cowboy_req:has_resp_header(3)[cowboy_req:has_resp_header(3)] - Is the given response header set?
 * link:man:cowboy_req:delete_resp_header(3)[cowboy_req:delete_resp_header(3)] - Delete a response header
 * link:man:cowboy_req:set_resp_body(3)[cowboy_req:set_resp_body(3)] - Set the response body

doc/src/manual/cowboy_req.resp_header.asciidoc

@@ -0,0 +1,61 @@
+= cowboy_req:resp_header(3)
+
+== Name
+
+cowboy_req:resp_header - Access the named HTTP header set for the response
+
+== Description
+
+[source,erlang]
+----
+resp_header(Name, Req)          -> resp_header(Name, Req, undefined)
+resp_header(Name, Req, Default) -> binary() | Default
+
+Name    :: binary()
+Req     :: cowboy_req:req()
+Default :: any()
+----
+
+Return the currently set response header value for the given HTTP header.
+
+== Arguments
+
+Name::
+
+Desired response HTTP header name as a binary.
+
+Req::
+
+The Req object.
+
+Default::
+
+Default value returned when the header is missing.
+
+== Return value
+
+The binary value for the given HTTP header name.
+
+== Changelog
+
+* *2.0*: Function introduced.
+
+== Examples
+
+.Get the response header with the given name
+[source,erlang]
+----
+HeaderValue = cowboy_req:resp_header(<<"x-test-header">>, Req).
+----
+
+.Get the response header with the given name and a default
+[source,erlang]
+----
+HeaderValue = cowboy_req:resp_header(<<"x-test-header">>, Req, <<"bar">>).
+----
+
+== See also
+
+link:man:cowboy_req(3)[cowboy_req(3)],
+link:man:cowboy_req:set_resp_headers(3)[cowboy_req:resp_headers(3)]
+link:man:cowboy_req:set_resp_header(3)[cowboy_req:set_resp_header(3)]

doc/src/manual/cowboy_req.resp_headers.asciidoc

@@ -0,0 +1,45 @@
+= cowboy_req:resp_headers(3)
+
+== Name
+
+cowboy_req:resp_headers - Access HTTP headers set for the response
+
+== Description
+
+[source,erlang]
+----
+resp_headers(Req) -> cowboy:http_headers()
+
+Req :: cowboy_req:req()
+----
+
+Return all HTTP response headers.
+
+== Arguments
+
+Req::
+
+The Req object.
+
+== Return value
+
+Headers are returned as a map with keys being lowercase
+binary strings, and values as binary strings.
+If no response headers have been added the empty map is returned.
+
+== Changelog
+
+* *2.0*: Function introduced.
+
+== Examples
+
+.Get all response headers
+[source,erlang]
+----
+Headers = cowboy_req:resp_headers(Req).
+----
+
+== See also
+
+link:man:cowboy_req(3)[cowboy_req(3)],
+link:man:cowboy_req:set_resp_headers(3)[cowboy_req:set_resp_headers(3)]

doc/src/manual/cowboy_req.set_resp_headers.asciidoc

@@ -0,0 +1,51 @@
+= cowboy_req:set_resp_headers(3)
+
+== Name
+
+cowboy_req:set_resp_headers - Set several response headers
+
+== Description
+
+[source,erlang]
+----
+set_resp_headers(Headers, Req) -> cowboy_req:req()
+
+Headers :: cowboy:http_headers()
+Req     :: cowboy_req:req()
+----
+
+Add all given headers to the response headers.
+If a given header key already exists in the currently set
+response-header map the given value will overwrite the old.
+
+== Arguments
+
+Headers::
+
+A map with keys and values as binary strings.
+Key values should be lowercase to function properly.
+
+Req::
+
+The Req object.
+
+== Return value
+
+A request object updated with the given response headers.
+
+== Changelog
+
+* *2.0*: Function introduced.
+
+== Examples
+
+.Get all response headers
+[source,erlang]
+----
+Req1 = cowboy_req:set_resp_headers(#{<<"x-header-test">> => <<"1">>}, Req0).
+----
+
+== See also
+
+link:man:cowboy_req(3)[cowboy_req(3)],
+link:man:cowboy_req:resp_headers(3)[cowboy_req:resp_headers(3)]