protoc-gen-grpc-gateway-es

Generate TypeScript client for gRPC API exposed via grpc-gateway. Powered by protobuf-es framework and bun toolchain.

Philosophy

The plugin walks over the proto files and converts

• protobuf messages to TypeScipt types and
• protobuf RPC to RPC JavaScript classes.

The RPC JavaScript class contains data about protobuf RPC and two useful methods, the signature of the class is

class RPC<RequestMessage, ResponseMessage> = {
  // HTTP method of the RPC. If not specified by google.api.http option defaults
  // to `POST`.
  readonly method: `DELETE` | `GET` | `PATCH` | `POST` | `PUT`;
  // URL path of the RPC. If not specified by the google.api.http option defaults
  // to "$proto_package.$service_name/$method_name".
  readonly path: string;
  // Optional: the path to body in the RequestMessage, only if specified by the
  // google.api.http option.
  readonly bodyKey?: string;
  /**
   * Creates a JavaScript Request object which can be used directly with fetch API.
   * If you are using other HTTP client, you can read the request properties from
   * the Request object - in that case read the usage caveats below.
   * @see https://developer.mozilla.org/en-US/docs/Web/API/Request
   * @param config the request configuration for the RPC
   * @param params the request message for the RPC as defined in the proto file
   */
  createRequest: (c: RequestConfig, m: RequestMessage) => Request;
  /**
   * Simple identity function that just types the input as ResponseMessage.
   * Usefull for TypeScript code to assing a type to the response.
   */
  responseTypeId: (r: any) => ResponseMessage;
};

Unlike many other gRPC-to-TypeScript generators, this one tries to be as minimal as possible, we don't do any extra de/-serialization for you, but we are using the TypeScript type system to provide more safety via type aliases and the runtime.ts file generated alongside your files contains conversion helpers

• The well-known protobuf types google.protobuf.Timestamp is converted to JavaScript string by the gRPC-gateway. The string contains date-time in ISO-8601 date format, you can convert that to JavaScript Date simply by passing it to the Date constructor or to the Data.parse static method. Conversion of Date object to the ISO string is simple with Date#toISOString method. There is no conversion helper in the runtime.ts module.
• Well-known protobuf type google.protobuf.Duration is converted to JavaScript string by the grpc-gateway. The string contains float of seconds with the s suffix, there is no appropriate JS type for that.
• The protobuf bytes type is converted to JavaScript string containing base64 encoded bytes. This is generated as type alias BytesString, preventing you from using it as a regular string in TypeScript. There are helper functions in the runtime.ts module for conversion from/to UInt8Array.
• The protobuf int64 type is converted to JavaScript string containing the ingerer. The gRPC-gateway does that to avoid overflow and loss of precision for very large numbers. This is generated as type alias BigIntString preventing you from using it as a regular string in TypeScript. There are helper functions in the runtime.ts module for conversion from/to BigInt.

Usage

The usage has two phases. First you need to generate the {Java,Type}Script files and then use them in your app.

Generate {Java,Type}Script files

This package is published as protoc-gen-grpc-gateway-es NPM module which contains the executable Node.js script. To use it in your buf generation project, write a shell script that will invoke the executable via NPX

#!/bin/sh

npx protoc-gen-grpc-gateway-es

Add the execute attribute to the script

chmod +x ./path/to/your/script.sh

And set it as a plugin in buf.gen.yaml

# buf.gen.yaml
version: v1
managed:
  enabled: true
  go_package_prefix:
    default: example/package/prefix
    except:
      - buf.build/googleapis/googleapis
      - buf.build/grpc-ecosystem/grpc-gateway
plugins:
  - name: es
    out: path/to/output/directory
    opt: target=ts,import_extension=none
    path: ./path/to/your/script.sh

If you need some intro to buf generate there is a tutorial on buf website.

You need to change:

• managed.go_package_prefix.default to your package prefix,
• plugins[0].out to the output directory of your choice,
• plugins[0].path to the path of the shell script which invokes the protoc-gen-grpc-gateway-es via NPX.

Then run buf generate (assuming you have properly installed and configured the buf) and it will generate the TypeScript files for you.

If you want to generate JavaScript instead of TypeScript, just pass change the plugin option opt: target=js. The list of all plugin options is here. For reason behind option import_extension=none see the caveats.

Note on formatting

To simplify the development, this plugin is not concerned with pretty printed output. The generated files are readable, but if your eyes are bleeding, use your favorite formatter after the files generation, e.g.

npx prettier --write gen/es/

Usage in app code

The generated files rely on browser API, i.e. it is anticipated you will use it in the browser only, usage in Node.js is untested, but in theory should work, at least in Node.js>=18

The generated files contain all the the protobuf messages as TypeScript types, all the protobuf enums as TypeScript enums and protobuf methods as RPC JavaScript classes. There is also a top-level runtime.ts file which contains the constructor of RPC class and a few helper TypeScript types and functions.

The typical usage with fetch might look like this.

import { SomeService_SomeMethod, type SomeMethodRequest } from "./gen/es/example/package/prefix/some_service_pb.ts";
import { type RequestConfig } from "./gen/es/runtime.ts"

const getBearerToken = () => {
  // your getter for bearer token in you app
  return `XYZ`;
}

const requestConfig: RequestConfig = {
  basePath: "https://example.test/api/v1",
  bearerToken: getBearerToken
};

const someMethodRequest: SomeMethodRequest = {
  flip: "flop",
}

// this is not required, but let's say we want to abort the request after 5 seconds
const signal = AbortSignal.timeout(5_000);

const request = SomeService_SomeMethod.getRequest(config, variables)

const serviceMethodCall = fetch(request, { signal }).then(response => {
  if (response.ok) {
    // type the response with the `responseTypeId` identity function, only
    // needed in TypeScript. If you are concerned with extra micro-task generated
    // by the `.then` call, you can type the `response.json()` with TypeScript
    // `as` keyword `response.json() as Promise<SomeMethodResponse>`
    return response.json().then(SomeService_SomeMethod.responseTypeId)
  }
  // reject the non-succesfull (non 2xx status code) response or do other things in your app
  return Promise.reject(response)
})

Note that the gRPC-gateway always returns a JSON, so respone.json() is safe here. In other APIs you might obtain non-JSON response and calling response.json() blindly would be a mistake.

You will likely create a wrapper function around the RPC class since the logic will be probably the same for all RPCs. We don't provide this wrapper since we consider it app-specific, but it might look something like this.

import { SomeService_SomeMethod } from "./gen/es/example/package/prefix/some_service_pb.ts";
import { type RPC, type RequestConfig } from "./gen/es/runtime.ts"

// this is usually constant for all RPC's in one API
const requestConfig: RequestConfig = {
  basePath: "https://example.test/api/v1",
  bearerToken: getBearerToken
};

// The generic types `RequestMessage` and `ResponseMessage` are inferred from the `RPC` passed as an argument
const fetchWrapRPC = <RequestMessage, ResponseMessage>(
  rpc: RPC<RequestMessage, ResponseMessage>
) => {
  return (
    variables: RequestMessage,
    { signal }: { signal?: AbortSignal } = {}
  ) => {
    return fetch(rpc.createRequest(requestConfig, variables), { signal })
      .then((response) => {
        if (response.ok) {
          // avoiding the `.then` call by using `as` keyword
          return response.json() as Promise<ResponseMessage>;
        }
        return Promise.reject(response);
      });
  };
};

// use the wrapper for generated RPC
const someServiceSomeMethodAsyncFunction = fetchWrapRPC(SomeService_SomeMethod);

// example of AbortController that you can abort imperetively later
const abortController = new AbortController();

// call the async function which accepts the request message and returns a promise of response JSON
const responseJSON = await someServiceSomeMethodAsyncFunction(
  { signal: abortController.signal }
  { flip: "flop" },
);

Usage caveats

1. The generated TypeScript files import other files with .js extension, this can be changed in the plugin configuration and I recommend setting import_extension=none which produces extension-less imports, otherwise your bundler or test framework might fail to resolve the imports.

2. The protobuf oneof are generated into the TypeScript as union, i.e. the message

   // flip.proto
   
   message Flip {
     string flap = 1;
     oneof toss {
       bool heads = 2;
       bool tails = 3;
     }
   }

   is generated as

   // flip_pb.ts
   
   export type Flip = { flap?: string } & (
    | { heads?: boolean; }
    | { tails?: boolean; }
   );

   this captures the mutual exclusivity but is a little cumbersome to work with in TypeScript, because if you attempt to access flip.heads the compiler complains that heads might not be defined. This forces you to use the JavaScript in operator which acts as a type guard. It is little inconvenient to use it each time you want to access the oneof field, but it is the proper way to tackle this problem.

   let test = flip.heads; // ❌ TS error: Object is possibly 'undefined'.
   if ("heads" in flip) {
     test = flip.heads; // ✅ OK, the `heads` is the `oneof` field
     test = flip.tails; // ❌ TS error: the `heads` and `tails` are mutually exclusive
   }

3. We decided to generate the JavaScript Request object for you, which is neatly compatible with the fetch API. Unfortunately, the Request object has a few quirks inherited from the streaming nature of the fetch. If you would ever need to read the body of the Request, you'll find it is a ReadableStream object and as such it is uneasy to obtain it's value. The most straight-forward way to consume the stream is to pass it to the Response object and then read it asynchronously

   const request = SomeService_SomeMethod.getRequest(config, variables);
   const requestBodyAsText = await(new Response(request.body).text());

   you can as well parse the body to a string with Response#json you know from the fetch API responses. After this call the readable stream will be consumed and no longer available, so if you read the body of the Request you can no longer use the Request object for the fetch API call 😒 You need to create a new Request object, where the constructor allows you clone the original request and you can pass in the old body you have read as a new body.

   // here passing the original request and the old body which was read into a text.
   const requestClone = new Request(request, { body: requestBodyAsText });

   The fetch API has identical signature so you can pass the same parameters to fetch

   // instead of creating a new Request object, you can pass the arguments directly to fetch call
   const response = await fetch(request, { body: requestBodyAsText });

   But you will most likely read the Request to use other network library than fetch. In any case, the runtime.ts library exports all of it's internals so you can use it as a plumbing in case you don't like the RPC#createRequest method 😉.

Development

First, read the Protobuf-ES: Writing Plugins and familiarize yourself with the Bun toolkit.

Use test-driven development, first write a failing test with feature you want to implement and then change the code.

Folders and their meaning

• /options/ - when you want to read options (a.k.a. extensions) from the proto files, and the options are non-scalar, such as

  option (google.api.http) = {get: "/v1/{name_test=projects/*/documents/*}:customMethod"};

  where the value of the google.api.http is an object, the protobuf-es framework requires you to have prepared the object types as @bufbuild/protobuf/Message JavaScript classes. Jere we are using buf to convert all options commonly used in gRPC-gateway into the required messages classes. There is a script bun run generateOptions which outputs the JavaScript classes into the /options/ folder, from which we import the classes during generation.

• /src/ - the main source code of this plugin

  • index.ts - instantiates the plugin with protobuf-es framework
  • generate.Ts.ts - the main logic of the plugin,
  • helpers.ts - various helpers for the plugin,
  • runtime.ts - this file is not used during generation, but contains common code for the runtime - the file is coppied by the plugin into the output folder and other generated files imports common logic from there.

• /tests/ - the test files, written using bun test API, you can run the test from CLI with bun test in the root of this repo or use bun plugin for your IDE to run and debug the tests selectivelly (highly recommended). There is an e2e setup which abstracts the protoc generation. The test framework accepts string representing a proto file, uses buf "black-magic" to resolve all proto dependencies and prepares the CodeGeneratorRequest¹, which is then passed to our logic and you can assert the generated TypeScript code.

  The generated code and your asserts are compiled via tsc so formatting nuances and comments are stripped away and the syntax of both values is verified before the test. Each test case is selfcontained, you must pass in valid proto file content and you obtain all generated TypeScript files.

• /tools/go - the shell script for invoking GO libraries with pinned version.

Development caveats

1. The bun is used also as a package manager, use bun add for adding dependencies, bun run for running NPM scripts or bunx instead of npx.
2. Beware that bun and buf are two different things and easy to confuse, it is easy to make mistake like running bun command with buf and vice versa.
3. Because buf can only read proto files from the file-system, each test writes a temporary file into /tests/proto/. The name of the file passed to getCodeGeneratorRequest function in the test is the actual name of the file created in /tests/proto/ directory, therefor each test must use unique file name. I usually name the file loosely after the test-case.

Footnotes

1. the protoc feeds the plugin with gRPC message CodeGenerationRequest on stdin and awaits the gRPC CodeGeneraionResponse on stdout. ↩