Support more message kinds as parameter types

[torkelrogstad]

Based on my reading of isWKTWithScalarJSONMapping and its usage, it seems like the only messages that's supported for parameters are primitive wrappers and google.protobuf universe. Would be great to also support more types from the google.type universe. I'm interested in using google.type.Date, at least.

[emcfarlane]

Hey @torkelrogstad you are correct, currently there is no custom formatting for JSON types (see this related issue that asks for google.type.Date). The parameter mapping uses the proto JSON representation and is restricted to these subset of types. Adding custom formats would have to be done with a custom JSONCodec. It would need to alter the methods MarshalAppendField and UnmarshalField to handle the date type marshalling. Hope that helps!

[rauanmayemir]

I too am interested in this.

@emcfarlane Followed your advise and started looking into JSONCodec. However, the MarshalAppendField function is just for pulling response_body fields, encoding still happens in MarshalAppend which is just a proxy for protojson.MarshalOptions.MarshalAppend.

[emcfarlane]

@rauanmayemir correct, to do custom JSON encoding that isn't parameter methods you would need to alter the MarshalAppend methods as well. This would have to be respected by both the client and the server so would not be a compatible with other implementations across the different language runtimes. However if all your clients are controlled by you then using the custom JSON methods would be an option.

[rauanmayemir]

Yeah, it's a bit too invasive just to have google.type.Date as string, so I tabled the idea for now.