Generate a JSON client

[stephenh]

Generate a JSON client

[amaury1729]

To make it really generic, we could also:

1. Change the signature of the request function to take

interface Rpc {
-  request(service: string, method: string, data: Uint8Array): Promise<Uint8Array>;
+  request<Req extends Codec, Res extends Codec>(service: string, method: string, req: Req): Promise<Res>;
}

where Codec is just:

// This is the interface that's already implemented by all types in ts-proto,
// i only gave it a name
interface Codec<T> {
  encode(message: T, writer: Writer = Writer.create()): Writer;
  decode(input: Uint8Array | Reader, length?: number): T;
  fromJSON(object: any): T;
  fromPartial(object: DeepPartial<T>): T;
  toJSON(message: T): unknown;
}

2. Then, it would be the user's responsability, when implementing the Rpc interface, to decide which wire format to use:

const implWithUint8Array: Rpc = {
  request<Req, Res>(service: string, method: string, req: Req): Promise<Res> {
    const data = Req.encode(req).finish();

    // Do whatever you used to do before, e.g. gRPC
    const wireResponse = ...;

    return Res.decode(new Reader(wireResponse))
  }
}

const implWithJSON: Rpc = {
  request<Req, Res>(service: string, method: string, req: Req): Promise<Res> {
    const data = Req.toJSON(req);

    // Do whatever you used to do before, e.g. gRPC with JSON
    const wireResponse = ...;

    return Res.fromJSON(wireResponse);
  }
}

Advantages:

• no need for an additional protoc option
• allow users to use Uint8Array, JSON for wire transfer... or do other more fancy stuff.

[alecthomas]

I think ideally it would be possible to pass a protoc option to specify which wire formats to generate. This would be nice because JSON-only clients then wouldn't need to import the JS protobuf package.

[stephenh]

@alecthomas yeah, that is a good point. We'd only needed protobuf/twirp for our rpc/services, so was all we've implemented so far...

The service impl code is fairly straightforward:

https://github.com/stephenh/ts-proto/blob/master/src/main.ts#L725

And I think really it'd just be generateRegularRpc function that could be the first place to add some conditional "if output type" type logic:

https://github.com/stephenh/ts-proto/blob/master/src/main.ts#L695

Would you be interesting in tacking a crack at this?

I might be able to hack on this at some point, but all the better if you'd like to, and then could verify the impl / usage / etc. within your project / ecosystem.

[isherman]

I started to take a look at what would be involved here.

Unfortunately, protobuf.js does not support encoding/decoding to/from canonical proto3 JSON: protobufjs/protobuf.js#1304

It looks like it's partially implemented, but lacking support for important well-known-types like Timestamp and Duration.

And google's JS protobuf library has no support at all: protocolbuffers/protobuf-javascript#95

Do you see any way forward?

[isherman]

It looks like there are some open PRs that would help, e.g. protobufjs/protobuf.js#1258

Maybe the way forward is to implement this using protobufjs, without support for those well-known types, and then either fork protobuf.js, patch it at runtime, or wait for it to be fixed upstream.

[stephenh]

Hey @isherman apologies for the really late reply here. It'd be awesome if you could poke around at this.

Per the protobuf.js PRs, I think that shouldn't be a problem, because ts-proto implements its own direct support for the proto3 JSON protocol.

I.e. here is where we generate Message.fromJSON methods and handle timestamps:

https://github.com/stephenh/ts-proto/blob/master/src/main.ts#L759

We don't handle encoding/encoding Durations yet.

So, in theory, a JSON client would just be some glue that takes the service interfaces and makes a <Service>JsonClient that uses ts-proto's existing fromJSON/toJSON methods to serde the messages.

[disjukr]

@amaurymartiny Agree. In my case, I also need the Res codec too.

interface Rpc {
-  request(service: string, method: string, data: Uint8Array): Promise<Uint8Array>;
+  request<Req extends Codec, Res extends Codec>(
+    service: string,
+    method: string,
+    data: Uint8Array,
+    req: Req,
+    res: Res
+  ): Promise<Uint8Array>;
}

[isherman]

Thanks for picking this up @disjukr, @amaurymartiny, @stephenh.
I lost momentum on #106 when the motivation for JSON serialization became less clear in my application. Will close that now.

Your approach looks more general, an improvement for sure. One tradeoff is it's a breaking change.
But I'm no longer a stakeholder here, so I defer to the maintainer!

[vtolstov]

any moving forward for this issue?