!README.md

Message Passing in JS

A simple function to handle a comunication over TCP via JSON using js generators.

Usage

Write a generator for each side of the conversation. To send or receive a message at some point just yield with one of the following functions

import { awaitMessage, sendMessage } from './mp.js'

function* () {
  ...
  yield sendMessage({ msg: 'hi', x: [1, 2, 3] })
  ... 
}
  
function* () {
  ...
  const { msg, x } = yield awaitMessage()
  ... 
}

TODO

• Maybe some better names:

  sendMessage(obj) -> send(obj)

  awaitMessage() -> receive()

  runMessagePassing(socket, actorFn) -> spawn(socket, actorFn)

_client.js

import { Socket } from 'net'
import { awaitMessage, runMessagePassing, sendMessage } from './mp.js'

function* clientHandler() {
    console.log('Client sending message to server')
    yield sendMessage('client says hi!')

    const msg1 = yield awaitMessage()
    console.log('Server:', msg1)

    console.log('Client sending message to server')
    yield sendMessage('client says goodbye!')
}

const client = new Socket()

client.connect(8080, 'localhost', () => {
    console.log('Connected client to localhost:8080')
    runMessagePassing(client, clientHandler)
})

_server.js

import { Server } from 'net'
import { awaitMessage, runMessagePassing, sendMessage } from './mp.js'

function* serverHandler() {
    const msg1 = yield awaitMessage()
    console.log('Client:', msg1)

    console.log('Server sending message to client')
    yield sendMessage('server says hi!')

    const msg2 = yield awaitMessage()
    console.log('Client:', msg2)
}

const server = new Server(socket => {
    console.log(`New client on localhost:8080`)
    runMessagePassing(socket, serverHandler)
})

server.listen(8080, 'localhost', () => {
    console.log('Started server on localhost:8080')
})

mp.js

export function sendMessage(message) {
    return { type: 'send', value: message }
}

export function awaitMessage() {
    return { type: 'await' }
}

export function runMessagePassing(socket, handler) {
    const queue = []
    const it = handler()
    let lastAction = null // null if ready to process next action

    const advance = () => {
        console.log('advance()')

        if (lastAction === null) {
            lastAction = it.next()
        }
        if (lastAction.done) {
            console.log('done!')
            return
        }

        const payload = lastAction.value

        if (payload.type === 'send') {
            process.stdout.write('Sending: ')
            console.dir(lastAction, { depth: null })

            // Handle "send" actions
            socket.write(JSON.stringify(payload.value) + '\n')
            lastAction = null
        } else if (payload.type === 'await') {
            if (queue.length === 0) {
                return
            }

            const response = queue.pop()
            lastAction = it.next(response)
        } else {
            throw 'Invalid action'
        }

        setTimeout(advance, 0)
    }

    // Handle "await" actions
    socket.on('data', data => {
        console.dir(data.toString(), { depth: null })
        const response = JSON.parse(data.toString())

        queue.push(response)

        process.stdout.write('Received: ')
        console.dir(response, { depth: null })

        setTimeout(advance, 0)
    })

    setTimeout(advance, 0)
}

output.txt

//
// Server
//
Started server on localhost:8080
New client on localhost:8080
advance()
'"client says hi!"\n'
Received: 'client says hi!'
advance()
Client: client says hi!
Server sending message to client
advance()
Sending: { value: { type: 'send', value: 'server says hi!' }, done: false }
advance()
'"client says goodbye!"\n'
Received: 'client says goodbye!'
advance()
Client: client says goodbye!
advance()
done!

//
// Client
//
Connected client to localhost:8080
advance()
Client sending message to server
Sending: { value: { type: 'send', value: 'client says hi!' }, done: false }
advance()
'"server says hi!"\n'
Received: 'server says hi!'
advance()
Server: server says hi!
Client sending message to server
advance()
Sending: { value: { type: 'send', value: 'client says goodbye!' }, done: false }
advance()
done!