Goals

• Idiomatic TypeScript/ES6 types
  • ts-proto is a clean break from either the built-in Google/Java-esque JS of protoc and protobufjs
  • (Techically the protobufjs/minimal package is used for actually reading/writing bytes.)
• TypeScript-first output
• Interfaces over classes
  • As much as possible, types are just interfaces (sometimes with prototype-driven defaults) so you can work with messages just like regular hashes/data structures.
• Only supports codegen *.proto-to-*.ts workflow, currently no runtime reflection/loading of dynamic .proto files
• Currently ambivalent about browser support, current focus is on Node/server-side use cases

Example Types

The generated types are "just data", i.e.:

export interface Simple {
  name: string;
  age: number;
  createdAt: Date | undefined;
  child: Child | undefined;
  state: StateEnum;
  grandChildren: Child[];
  coins: number[];
}

Along with encode/decode factory methods:

export const Simple = {
  encode(message: Simple, writer: Writer = Writer.create()): Writer {
    ...
  },

  decode(reader: Reader, length?: number): Simple {
    ...
  },

  fromJSON(object: any): Simple {
    ...
  },

  fromPartial(object: DeepPartial<Simple>): Simple {
    ...
  },

  toJSON(message: Simple): unknown {
    ...
  },
};

This allows idiomatic TS/JS usage like:

const bytes = Simple.encode({ name: ..., age: ..., ... }).finish();
const simple = Simple.decode(Reader.create(bytes));
const { name, age } = simple;

Which can dramatically ease integration when converting to/from other layers without creating a class and calling the right getters/setters.

Highlights

• A poor man's attempt at "please give us back optional types"

  Wrapper types, i.e. google.protobuf.StringValue, are mapped as optional values, i.e. string | undefined, which means for primitives we can kind of pretend that the protobuf type system has optional types.

• Timestamp is mapped as Date

• fromJSON/toJSON support the canonical Protobuf JS format (i.e. timestamps are ISO strings)

Usage

ts-proto is a protoc plugin, so you run it by (either directly in your project, or more likely in your mono-repo schema pipeline, i.e. this or this):

• Add ts-proto to your package.json
• Run npm install to download it
• Invoke protoc with a plugin parameter like:

protoc --plugin=node_modules/ts-proto/protoc-gen-ts_proto ./batching.proto -I.

Supported options:

• Right now, ts-proto always generates Twirp service implementations for any RPC services, simply because that is what we use. Adding an option to disable Twirp and support GRPC is on the todo list.
• If you pass --ts_proto_opt=context=true, the Twirp services will have a Go-style ctx parameter, which is useful for tracing/logging/etc. if you're not using node's async_hooks api due to performance reasons.

Assumptions

• TS/ES6 module name is the proto package

Todo

• Better Long support; currently any values greater than Number.MAX_SAFE_INTEGER blow up at runtime
• Model OneOfs as an ADT
• Support the string-based encoding of duration in fromJSON/toJSON
• Support bytes as base64 encoded strings in fromJSON/toJSON
• Support the json_name annotation

Typing Approach

• Missing fields on read
  • When decoding from binary, we setup a prototype for our returned object, which has default values.
    • This assumes missing keys trigger the default value, e.g. storing key=undefined would subvert the approach
  • When decoding from JSON, we may have missing keys.
    • We could convert them to our prototype.
  • When using an instantiated object, our types enforce all keys to be set.

OneOf Handling

Currently fields that are modeled with oneof either_field { string field_a; string field_b } are generated as field_a: string | undefined; field_b: string | undefined.

This means you'll have to check if object.field_a and if object.field_b, and if you set one, you'll have to remember to unset the other.

It would be nice/preferable to model this as an ADT, so it would be:

object.either_field = { kind: 'field_a', value: 'name' };

However this differs sufficiently from the wire-level format that there might be wrinkles.

An original design notion of ts-proto was that ideally we could get JSON off the wire and immediately cast it to the generated ts-proto types, but features like oneof ADTs require walking the JSON looking for things to massage.

Similarily, writing a ts-proto object as protobuf-compliant JSON would not be a straight JSON.stringify(tsProtoObject).

(Idea: maybe either_field exists in the prototype, and wraps/manages the underlying primitive values.)

Primitive Types

Protobuf has the somewhat annoying behavior that primitives types cannot differentiate between set-to-defalut-value and unset.

I.e. if you have a string name = 1, and set object.name = '', Protobuf will skip sending the tagged name field over the wire, because its understood that readers on the other end will, when they see name is not included in the payload, return empty string.

ts-proto models this behavior, of "unset" values being the primitive's default. (Technically by setting up an object prototype that knows the default values of the message's primitive fields.)

If you want fields where you can model set/unset, see Wrapper Types.

Wrapper Types

In core Protobuf, while unset primitives are read as default values, unset messages are returned as null.

This allows a cute hack where you can model a logical string | null by creating a field that is a message (can be null) and the message has a single string value (for when the value is not null).

Protobuf has several built-in types for this pattern, i.e. google.protobuf.StringValue.

ts-proto understands these wrapper types and will generate google.protobuf.StringValue name = 1 as a name: string | undefined.

This hides some of the StringValue mess and gives a more idiomatic way of using them.

Granted, it's unfortunate this is not as simple as marking the string as optional.

Current Status of Optional Values

• Required primitives: use as-is, i.e. string name = 1.
• Optional primitives: use wrapper types, i.e. StringValue name = 1.
• Required messages: not available
• Optional primitives: use as-is, i.e. SubMessage message = 1.