feat: header-wise max_header_value_lenght

Author: MarkoMin

doc/src/manual/cowboy_http.asciidoc

@@ -141,7 +141,8 @@ Maximum length of header names.
 
 max_header_value_length (4096)::
 
-Maximum length of header values.
+Maximum length of header values. Value can be an integer (same value for all headers)
+or a function (enables header-wise limitation).
 
 max_headers (100)::
 

src/cowboy_http.erl

@@ -44,7 +44,7 @@
 	max_authority_length => non_neg_integer(),
 	max_empty_lines => non_neg_integer(),
 	max_header_name_length => non_neg_integer(),
-	max_header_value_length => non_neg_integer(),
+	max_header_value_length => non_neg_integer() | fun((HeaderName::binary()) -> non_neg_integer()),
 	max_headers => non_neg_integer(),
 	max_keepalive => non_neg_integer(),
 	max_method_length => non_neg_integer(),
@@ -703,8 +703,8 @@ parse_hd_before_value(<< $\s, Rest/bits >>, S, H, N) ->
 parse_hd_before_value(<< $\t, Rest/bits >>, S, H, N) ->
 	parse_hd_before_value(Rest, S, H, N);
 parse_hd_before_value(Buffer, State=#state{opts=Opts, in_state=PS}, H, N) ->
-	MaxLength = maps:get(max_header_value_length, Opts, 4096),
-	case match_eol(Buffer, 0) of
+	MaxLength = get_max_header_value_len(Opts, N),
+    case match_eol(Buffer, 0) of
 		nomatch when byte_size(Buffer) > MaxLength ->
 			error_terminate(431, State#state{in_state=PS#ps_header{headers=H}},
 				{connection_error, limit_reached,
@@ -715,6 +715,13 @@ parse_hd_before_value(Buffer, State=#state{opts=Opts, in_state=PS}, H, N) ->
 			parse_hd_value(Buffer, State, H, N, <<>>)
 	end.
 
+get_max_header_value_len(#{max_header_value_length:=Max}, _HeaderName) when is_integer(Max) ->
+    Max;
+get_max_header_value_len(#{max_header_value_length:=MaxFun}, HeaderName) ->
+    MaxFun(HeaderName);
+get_max_header_value_len(_Opts, _HeaderName) ->
+    4096.
+
 parse_hd_value(<< $\r, $\n, Rest/bits >>, S, Headers0, Name, SoFar) ->
 	Value = clean_value_ws_end(SoFar, byte_size(SoFar) - 1),
 	Headers = case maps:get(Name, Headers0, undefined) of