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    redistribute

    0.0.3 • Public • Published






    Redistribute is a toolkit for building streaming real-time applications using Node.js, Redis Streams, WebSockets and localStorage, which aims to dramatically reduce the amount of code and cash required to write reliable, distributed, real-time applications with no single points of failure.

    Redistribute has two components, redistribute, the server package (a Node.js library), and redistribute-client, a browser and Node.js compatible client library,

    An example will look quite a bit like an example for a standard WebSocket library, with a few key differences:

    1. Redistribute Streams are distributed; any other server (and their clients) which is subscribed to a channel will receive the messages. No need for single points of failure, no need for vertically scaling a single Node.js instance, no need for the cluster module or other premature optimizations and complexities.

    2. Redistribute Streams are replayable; past messages can be re-read from the Redis stream after they have been originally sent (up to a configurable limit).

    3. Redistribute Streams are shardable; a fleet of worker machines can work together to handle messages in a stream via "Consumer Groups".

    Table of Contents

    1. About
    2. Examples
    3. Messages
    4. Server
    5. Client

    About

    Redistribute is powered by brand new features in the Redis Database - Streams! You should read the original blog post and the official Redis docs. Redistribute uses XREAD and XADD to read and write to Redis Streams, and exposes an API that allows easy creation of real-time WebSocket services. Note that we require brand new features, including the recently merged CLIENT UNBLOCK command - You can use the erulabs/redis-unstable image for Redis for now (this should land in stable redis before too long). Redistribute is meant to be a low level library, and not a full featured chat system, for example.

    Example

    Server

    // Connect to Redis5 instances
    const server = require('redistribute')([
      { host: '127.0.0.1', port: 6379 }
    ])
    // Hoist a Redistribute WebSocket server
    server.listen({
      key: '...', cert: '...', port: 8080
    })

    Client

    const client = require('redistribute-client')({
      targets: ['https://redistribute-api.demo:8080']
    })
    client.subscribe('myTestChannel')
    client.on('messages', (channel, messages) => {
      // TODO: Update chat app display with new messages!
    })
    client.publish('myTestChannel', 'TEST_MESSAGE', { foo: 'bar' })

    API Documentation

    Messages

    Messages events provide arrays of "Message" objects, which have the following properties:

    const Message = {
      offset: string,
      key: value,
      key2: value2...
    }

    For example, consider the following:

    // Server
    socket.emit('testChannel', 'TEST_MESSAGE', { foo: 'bar' })
    // Client
    client.on('messages', (channel, messages) => {
      // channel === "testChannel"
      // messages === [
      //  {
      //    offset: "1518951480106-0",
      //    TEST_MESSAGE: { foo: 'bar' } }
      // ]
    })

    Server

    Redistribute(options)

    Where "options" is an object with the following properties:

    Option Required Default Description
    targets yes - An array of Redis server URIs
    encode no JSON.stringify A function for encoding published objects
    decode no JSON.parse A function for decoding published objects

    Server Events

    • connect - A new socket has connected
    • error - An error has been encountered (connection to Redis failed, etc)

    Redistribute.listen(options)

    Where "options" is an object with the following properties:

    Option type Required Default Description
    key string yes - Filepath to SSL key
    cert string yes - Filepath to SSL certificate
    port number no 8080 Port number to listen on for websocket connections

    async Redistribute.publish(channel, ...)

    Send data upstream to the Redis service.

    await server.publish('myChannel', 'some', 'data')
    // returns with locally loaded messages and most recent offset

    Note that arguments after the channel name are in key-value pairs of two, matching the XADD Documentation. The exception is when the second argument is a number, in which case it is assumed to be a MAXLEN (Maximum stream length):

    // Delete old stream entries after ~ 5000 messages
    server.publish('myChannel', 5000, 'foo', 'bar')

    Redistribute.maxlen(channel, maxlength)

    Tells the server to prepend a MAXLEN argument to all XADD commands for this channel (Read more here). Note that this command only effects the current Redistribute instance - it is not propagated to other instances or persisted anywhere except memory.

    server.maxlen('myChannel', 5000)

    For dynamic channels, consider setting the MAXLEN during publishing

    Socket Events

    • disconnect - A socket has disconnected
    • subscribe - A socket has requested a subscription to a channel
    • unsubscribe - A socket no long wants messages from a channel
    • publish - A socket has a message to publish for a channel
    • messages - Messages have arrived from a subscribed channel

    Socket.subscribe(channel, offset)

    Argument type Required Default Description
    channel string yes - Channel identifier key
    offset string no $ Redis stream offset

    Socket.unsubscribe(channel)

    Unsubscribes a socket from a given channel. This is called automatically when a socket disconnects, if there is no existing disconnect handler defined.

    Argument type Required Default Description
    channel string yes - Channel to unsubscribe from

    Socket.emit(channel, messages)

    Send data to a connected socket

    Client

    Client(options)

    Where "options" is an object with the following properties:

    Option Required Default Description
    targets yes - An array of Redistribute server URIs
    encode no JSON.stringify A function for encoding published objects
    decode no JSON.parse A function for decoding published objects
    localStorage no true Automatically store retrieved messages

    Client Events

    • connect - Socket is connected to the server
    • disconnect - Socket has been disconnected from the server
    • messages - Messages have arrived from a subscribed channel
    • error - An error has been received from the server

    async Client.load(channel)

    Argument type Required Default Description
    channel string yes - Channel to load locally stored message for
    const { messages, lastOffset } = await client.load('myChannel')
    // returns with locally loaded messages and most recent offset

    async Client.subscribe(channel, offset)

    Argument type Required Default Description
    channel string yes - Channel to load locally stored message for
    offset string no $ Redis stream offset
    await client.subscribe('myChannel')
    // returns true if subscribe message sent successfully

    async Client.unsubscribe(channel)

    Argument type Required Default Description
    channel string yes - Channel to unsubscribe from
    await client.unsubscribe('myChannel')
    // returns true if unsubscribe message sent successfully

    async Client.publish(channel, ...)

    Argument type Required Default Description
    channel string yes - Channel to publish messages to

    The rest of the arguments are considered key-value pairs, to be used during the Redis Stream XADD. This means that the number of arguments after channel must be an even number. For example:

    // Examples of Client Publish
    await client.publish('test', 'foo', 'bar')
    // Success! Returns with new message offset
    await client.publish('test', 'foo')
    // Error! Invalid argument count!
    await client.publish('test', 'foo', { bar: "baz" })
    // Note that object arguments are stringified automatically
    await client.publish('test', 'foo', 'bar', 'baz', 'bam', 'words', 'things')
    // Success! We can post as many key-value pairs as desired

    Advanced Topics

    Restricting channels and messages (authentication)

    Redistribute has a set of default handlers for the subscribe and messages events - we simply pass them to Socket.subscribe and Server.publish directly (effectively meaning anyone can subscribe and publish to any channel). You can (can probably should!) overwrite that behavior to implement permissions and authentication by overwriting those event handlers:

    server.on('connect', socket => {
      // Handle subscription requests from users
      socket.on('subscribe', (channel, offset) => {
        if (userHasAccessToChannel(socket, channel))
          socket.subscribe(channel, offset)
      })
      // Handle messages from a user
      socket.on('messages', (channel, messages)) => {
        if (userHasAccessToChannel(socket, channel))
          server.publish(channel, messages)
      })
    })

    Maximum stream length (XADD MAXLEN)

    Redistribute can set a MAXLEN argument when performing XADDs (Read more here)

    // Set ahead of time, for specific channels
    // Limit the stream to the last 5000 messages
    // Note this setting only persists locally within this Node instance
    server.maxlen('myTestChannel', 5000)
     
    // When publishing on the server
    server.publish('myTestChannel', 5000, 'foo', 'bar')

    Filtering messages to end-users

    On the server, define a streamEvent handler, and intercept messages from Redis Stream which are on their way to end-users

    // This handler is not required (this is the default behavior!)
    server.on('streamEvent', (channel, message) => {
      // Ship messages to sockets who are subscribed to those channels
      // This handler is useful in situations where the server ought to take some action,
      // but it's not required to notify end-users of the message
      server.broadcast(channel, message)
    })

    Keywords

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    Install

    npm i redistribute

    DownloadsWeekly Downloads

    1

    Version

    0.0.3

    License

    MIT

    Unpacked Size

    32.4 kB

    Total Files

    36

    Last publish

    Collaborators

    • erulabs