From 6d6355723529ed3423c3d8b3c3ca9a29089e9f23 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Lo=C3=AFc=20Hoguin?= <essen@ninenines.eu>
Date: Mon, 6 Jun 2016 17:33:03 +0200
Subject: REST: If-None-Match uses weak Etag comparison

Was badly implemented previously.
---
 src/cowboy_rest.erl | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/cowboy_rest.erl b/src/cowboy_rest.erl
index d28c8e9..670e74b 100644
--- a/src/cowboy_rest.erl
+++ b/src/cowboy_rest.erl
@@ -741,7 +741,7 @@ if_none_match(Req, State, EtagsList) ->
 				undefined ->
 					precondition_failed(Req2, State2);
 				Etag ->
-					case lists:member(Etag, EtagsList) of
+					case is_weak_match(Etag, EtagsList) of
 						true -> precondition_is_head_get(Req2, State2);
 						false -> if_modified_since_exists(Req2, State2)
 					end
@@ -750,6 +750,14 @@ if_none_match(Req, State, EtagsList) ->
 		error_terminate(Req, State, Class, Reason, generate_etag)
 	end.
 
+%% Weak Etag comparison: only check the opaque tag.
+is_weak_match(_, []) ->
+	false;
+is_weak_match({_, Tag}, [{_, Tag}|_]) ->
+	true;
+is_weak_match(Etag, [_|Tail]) ->
+	is_weak_match(Etag, Tail).
+
 precondition_is_head_get(Req, State=#state{method=Method})
 		when Method =:= <<"HEAD">>; Method =:= <<"GET">> ->
 	not_modified(Req, State);
-- 
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