Fix issue ninenines#157 relating to daylight savings time.

src/cowboy_clock.erl

@@ -64,7 +64,20 @@ rfc2109(LocalTime) ->
 	{{YYYY,MM,DD},{Hour,Min,Sec}} =
 	case calendar:local_time_to_universal_time_dst(LocalTime) of
 	    [Gmt]   -> Gmt;
-	    [_,Gmt] -> Gmt
+	    [_,Gmt] -> Gmt;
+		[] ->
+			%% The localtime generated by cowboy_cookies may fall within
+			%% the hour that is skipped by daylight savings time. If this
+			%% is such a localtime, increment the localtime with one hour
+			%% and try again, if this succeeds, subtracting the max_age
+			%% from the resulting universaltime and converting to a local
+			%% time will yield the original localtime.
+			{Date, {Hour1, Min1, Sec1}} = LocalTime,
+			LocalTime2 = {Date, {Hour1 + 1, Min1, Sec1}},
+			case calendar:local_time_to_universal_time_dst(LocalTime2) of
+				[Gmt]   -> Gmt;
+				[_,Gmt] -> Gmt
+			end
 	end,
 	Wday = calendar:day_of_the_week({YYYY,MM,DD}),
 	DayBin = pad_int(DD),