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Scala-inspired Actors that use Redis as a message transport


Mutual is inspired by Scala's Actor model. Concurrency is managed by setting up Channels between participants. Remote channels are implemented by using Redis as a transport. Event channels provide an EventEmitter like interface. Builder methods, in combination with event-bubbling, can be used to build complex chains of asynchronous processing.

fs = require "fs"

{EventChannel} = require "mutual"
events = new EventChannel

# all error events will bubble-up here
events.on "error", (error) -> console.log error

# wrap a Node-style callback function
read = events.wrap(fs.readFile)

# use builder function to create an asynchronous control flow
do events.serially (go) ->
  go -> read("foo.txt", encoding: "utf8")
  go (text) -> console.log text

Remote channels are just event channels, which means you can swap them out without changing any code. Here's a simple express app that implements a chat interface:

http = require "http"
{EventChannel} = require "mutual"
events = new EventChannel

# all error events will bubble-up here
events.on "error", (error) -> console.log error

{getChannel,makeChannel} = do (channels = {}) ->
  makeChannel: (name) -> events.source name
  getChannel: (name) -> channels[name] ?= makeChannel(name)

express = require "express"
app = express()

app.use (request, response, next) -> 
  body = ""
  request.on "data", (data) -> body += data
  request.on "end", ->
    request.body = body

app.get '/:channel', (request, response) ->
  {channel} = request.params
  getChannel(channel).once "message", (message) ->
    response.send message '/:channel', (request, response) ->
  response.send 202, ""
  {channel} = request.params
  message = request.body
  getChannel(channel).emit "message", message


If you run this, you can do a GET to a channel URL (ex: /foo) and then POST a message to it.

    curl http://localhost:1337/foo &
    curl http://localhost:1337/foo -d "Hello"

The original GET will return the message.

Of course, this isn't much different from what we could do using EventEmitter, outside of utilizing the event bubbling for error events. However, this version also has a big limitation: it only works for one process. If we start to get lots of messages, we'll want to be able to run multiple processes, perhaps even across multiple machines.

With Mutual, all we need to do, basically, is change makeChannel so that it returns a RemoteChannel.

First, let's require the RedisTransport and RemoteChannel:

{RemoteChannel,EventChannel,RedisTransport} = require "../src/index"

Next, well instantiate the transport:

transport = new RedisTransport host: "localhost", port: 6379

Finally, we just change our makeChannel function:

makeChannel: (name) -> 
  channel = new RemoteChannel {name,transport}
  channel.forward(events, name)

The rest of our code remains the same. We've just moved to an implementation that will work across multiple process or machine boundaries by adding and modifying a few lines of code. The bulk of our application is unchanged.

Our final version of our little chat API can be found in the examples.

npm install mutual

In development - the interface is relatively stable, but we haven't done a lot of load and performance testing.