Return single element array with JSON-RPC is impossible?

[cl0ne]

When we have a method that returns list of structs, depending on the element count we will get completely different results:

• list with 2+ structs will give an expected array with 2+ objects;
• empty list will give an empty string (okay, I get it, we have no way differentiate empty list from empty strings);
• list with single struct will be stripped down to object instead of an array with single object (of course, we can work around this by wrapping result list with a single-field object, but that looks like an ugly hack).

The question is why encode_handler_payload unwraps single-element lists?

[vinoski]

This was apparently done in the very first version of the yaws_rpc module; see 1791e3d. My understanding is that the module was originally written to support Haxe, so perhaps it had/has a case that requires this.

[cl0ne]

I guess that replacing

yaws/src/yaws_rpc.erl

Lines 393 to 402 in ca704a9

	encode_handler_payload({response, [ErlStruct]}, ID, RpcType) ->
	encode_handler_payload({response, ErlStruct}, ID, RpcType);
	encode_handler_payload({response, ErlStruct}, ID, RpcType) ->
	StructStr =
	case RpcType of
	json -> json2:encode({struct, [{result, ErlStruct}, {id, ID},
	{"jsonrpc", "2.0"}]});
	haxe -> [$h, $x, $r | haxe:encode(ErlStruct)]
	end,
	{ok, StructStr}.

with

encode_handler_payload({response, ErlStruct}, ID, json) ->
    StructStr = json2:encode({struct, [
        {result, ErlStruct},
        {id, ID},
        {"jsonrpc", "2.0"}
    ]}),
    {ok, StructStr};

encode_handler_payload({response, [ErlStruct]}, ID, haxe) ->
    encode_handler_payload({response, ErlStruct}, ID, haxe);
encode_handler_payload({response, ErlStruct}, ID, haxe) ->
    StructStr = [$h, $x, $r | haxe:encode(ErlStruct)],
    {ok, StructStr}.

will fix the issue but breaks backward compatibility at the same time.

[vinoski]

Right, the backward compatibility issue is the problem with changing this.