Disable ws compression if constraints clash

When the client does not provide the "client_max_window_bits" option, the server must be able to handle a sliding window of up to 32,768 bytes. In case that the window has a lower limit set by options, compression must be disabled. Co-authored-by: Ignacio Martínez <[email protected]>
ninenines · Oct 7, 2021 · a6fd4f1 · a6fd4f1
1 parent 0f5c2f8
commit a6fd4f1
Showing 1 changed file with 6 additions and 2 deletions.
diff --git a/src/cow_ws.erl b/src/cow_ws.erl
@@ -133,6 +133,8 @@ negotiate_permessage_deflate1(Params, Extensions, Opts) ->
 			ignore;
 		{#{client_max_window_bits := CB}, _} when CB > ClientMaxWindowBits ->
 			ignore;
+		{Negotiated, _} when not is_map_key(client_max_window_bits_set, Negotiated), ClientMaxWindowBits < 15 ->
+			ignore;
 		{Negotiated, RespParams2} ->
 			%% We add the configured max window bits if necessary.
 			RespParams = case Negotiated of
@@ -165,12 +167,14 @@ negotiate_params([{<<"client_max_window_bits">>, Max}|Tail], Negotiated, RespPar
 		error ->
 			ignore;
 		CB when CB =< CB0 ->
-			negotiate_params(Tail, Negotiated#{client_max_window_bits => CB},
+			negotiate_params(Tail,
+				Negotiated#{client_max_window_bits => CB,
+					client_max_window_bits_set => true},
 				[<<"; client_max_window_bits=">>, Max|RespParams]);
 		%% When the client sends window bits larger than the server wants
 		%% to use, we use what the server defined.
 		_ ->
-			negotiate_params(Tail, Negotiated,
+			negotiate_params(Tail, Negotiated#{client_max_window_bits_set => true},
 				[<<"; client_max_window_bits=">>, integer_to_binary(CB0)|RespParams])
 	end;
 negotiate_params([{<<"server_max_window_bits">>, Max}|Tail], Negotiated, RespParams) ->