grpc-caller

An improved gRPC client.

Features

Promisifies request / response (Unary) calls if no callback is supplied
Promisifies request stream / response calls if no callback is supplied
Automatically converts plain javascript object to metadata in calls.
Adds optional retry functionality to request / response (Unary) calls.
Exposes expanded Request API for collecting metadata and status.

Installation

$ npm install grpc-caller

Overview

Improved unary calls

Works as standard gRPC client:

const caller = require('grpc-caller')
const PROTO_PATH = path.resolve(__dirname, './protos/helloworld.proto')
const client = caller('0.0.0.0:50051', PROTO_PATH, 'Greeter')
client.sayHello({ name: 'Bob' }, (err, res) => {
  console.log(res)
})

For unary calls, also promisified if callback is not provided:

client.sayHello({ name: 'Bob' })
  .then(res => console.log(res))

Which means means you can use is with async / await

const res = await client.sayHello({ name: 'Bob' })
console.log(res)

For Unary calls we expose retry option identical to async.retry.

const res = await client.sayHello({ name: 'Bob' }, {}, { retry: 3 })
console.log(res)

Improved request stream / response calls

Lets say we have a remote call writeStuff that accepts a stream of messages and returns some result based on processing of the stream input.

Works as standard gRPC client:

const call = client.writeStuff((err, res) => {
  if (err) console.error(err)
  console.log(res)
})

// ... write stuff to call

If no callback is provided we promisify the call such that it returns an object with two properties call and res such that:

call - the standard stream to write to as returned normally by grpc
res - a promise that’s resolved / rejected when the call is finished, in place of the callback.

Using destructuring we can do something like:

const { call, res } = client.writeStuff()
res
  .then(res => console.log(res))
  .catch(err => console.error(err))

// ... write stuff to call

This means we can abstract the whole operation into a nicer promise returning async function to use with async / await

async function writeStuff() {
  const { call, res } = client.writeStuff()
  // ... write stuff to call
  return res
}

const res = await writeStuff()
console.log(res)

Automatic `Metadata` creation

All standard gRPC client calls accept Metadata as first or second parameter (depending on the call type). However one has to manually create the Metadata object. This module uses grpc-create-metadata to automatically create Metadata if plain Javascript object is passed in.

// the 2nd parameter will automatically be converted to gRPC Metadata and
// included in the request
const res = await client.sayHello({ name: 'Bob' }, { requestid: 'my-request-id-123' })
console.log(res)

We can still pass an actual Metadata object and it will be used as is:

const meta = new grpc.Metadata()
meta.add('requestid', 'my-request-id-123')
const res = await client.sayHello({ name: 'Bob' }, meta)
console.log(res)

Request API

In addition to simple API above, the library provides a more detailed "Request" API that can be used to control the call details. The API can only be used for Unary and request streaming calls.

Unary calls

const req = new client
  .Request('sayHello', { name: 'Bob' }) // call method name and argument
  .withMetadata({ requestId: 'bar-123' }) // call request metadata
  .withResponseMetadata(true) // we want to collect response metadata
  .withResponseStatus(true) // we want to collect the response status
  .withRetry(5) // retry options

const res = await req.exec()  
// res is an instance of our `Response`
// we can also call exec() using a callback

console.log(res.response) // the actual response data { message: 'Hello Bob!' }
console.log(res.metadata) // the response metadata
console.log(res.status)   // the response status
console.log(res.call)     // the internal gRPC call

Request streaming calls

In case of request streaming calls if exec() is called with a callback the gRPC call stream is returned. If no callback is provided an object is returned with call property being the call stream and res property being a Promise fulfilled when the call is completed. There is no retry option for request streaming calls.

const req = new client.Request('writeStuff') // the call method name
    .withMetadata({ requestId: 'bar-123' })  // the call request metadata
    .withResponseMetadata(true) // we want to collect response metadata
    .withResponseStatus(true)   // we want to collect the response status

const { call, res: resPromise } = req.exec()

// ... write data to call

const res = await resPromise // res is our `Response`

console.log(res.response) // the actual response data
console.log(res.metadata) // the response metadata
console.log(res.status)   // the response status
console.log(res.call)     // the internal gRPC call

API Reference

Request

A Request class that encapsulates the request of a call.

Kind: global class

Request
- new Request(methodName, param)
- .withGrpcOptions(opts) ⇒ Object
- .withMetadata(opts) ⇒ Object
- .withRetry(retry) ⇒ Object
- .withResponseMetadata(value) ⇒ Object
- .withResponseStatus(value) ⇒ Object
- .exec(fn) ⇒ Promise | Object

new Request(methodName, param)

Creates a Request instance.

Param	Type	Description
methodName	`String`	the method name.
param	`\*`	the call argument in case of `UNARY` calls.