From 05c5378265275ddd01783e7f8c395575d3cc4e85 Mon Sep 17 00:00:00 2001
From: Zaiming Shi <zmstone@gmail.com>
Date: Thu, 6 May 2021 17:59:33 +0200
Subject: [PATCH] feat(http_lib): add normalise_headers API

---
 src/emqx_http_lib.erl        | 16 ++++++++++++++++
 test/emqx_http_lib_tests.erl |  5 +++++
 2 files changed, 21 insertions(+)

diff --git a/src/emqx_http_lib.erl b/src/emqx_http_lib.erl
index 9e86fe394..60f19e6bb 100644
--- a/src/emqx_http_lib.erl
+++ b/src/emqx_http_lib.erl
@@ -19,6 +19,7 @@
 -export([ uri_encode/1
         , uri_decode/1
         , uri_parse/1
+        , normalise_headers/1
         ]).
 
 -export_type([uri_map/0]).
@@ -91,6 +92,21 @@ do_parse(URI) ->
             normalise_parse_result(Map2)
     end.
 
+%% @doc Return HTTP headers list with keys lower-cased and
+%% underscores replaced with hyphens
+%% NOTE: assuming the input Headers list is a proplists,
+%% that is, when a key is duplicated, list header overrides tail
+%% e.g. [{"Content_Type", "applicaiton/binary"}, {"content-type", "applicaiton/json"}]
+%% results in: [{"content-type", "applicaiton/binary"}]
+normalise_headers(Headers0) ->
+    F = fun({K0, V}) ->
+                K = re:replace(K0, "_", "-", [{return,list}]),
+                {string:lowercase(K), V}
+        end,
+    Headers = lists:map(F, Headers0),
+    Keys = proplists:get_keys(Headers),
+    [{K, proplists:get_value(K, Headers)} || K <- Keys].
+
 normalise_parse_result(#{host := Host, scheme := Scheme0} = Map) ->
     Scheme = atom_scheme(Scheme0),
     DefaultPort = case https =:= Scheme of
diff --git a/test/emqx_http_lib_tests.erl b/test/emqx_http_lib_tests.erl
index 393d1ff86..a850da8f5 100644
--- a/test/emqx_http_lib_tests.erl
+++ b/test/emqx_http_lib_tests.erl
@@ -77,3 +77,8 @@ uri_parse_test_() ->
        end
       }
     ].
+
+normalise_headers_test() ->
+    ?assertEqual([{"content-type", "applicaiton/binary"}],
+                 emqx_http_lib:normalise_headers([{"Content_Type", "applicaiton/binary"},
+                                                  {"content-type", "applicaiton/json"}])).