Add support for range requests (RFC7233) in cowboy_rest

This is currently undocumented but is planned to be documented
in the next version.

test/handlers/ranges_provided_h.erl

@@ -0,0 +1,30 @@
+%% This module defines the ranges_provided callback
+%% and return something different depending on query string.
+
+-module(ranges_provided_h).
+
+-export([init/2]).
+-export([content_types_provided/2]).
+-export([ranges_provided/2]).
+-export([get_text_plain/2]).
+
+init(Req, State) ->
+	{cowboy_rest, Req, State}.
+
+content_types_provided(Req, State) ->
+	{[{{<<"text">>, <<"plain">>, []}, get_text_plain}], Req, State}.
+
+ranges_provided(Req=#{qs := <<"list">>}, State) ->
+	{[
+		{<<"bytes">>, get_text_plain_bytes},
+		{<<"pages">>, get_text_plain_pages},
+		{<<"chapters">>, get_text_plain_chapters}
+	], Req, State};
+ranges_provided(Req=#{qs := <<"none">>}, State) ->
+	{[], Req, State};
+%% Simulate the callback being missing in other cases.
+ranges_provided(_, _) ->
+	no_call.
+
+get_text_plain(Req, State) ->
+	{<<"This is REST!">>, Req, State}.