Feedme Javascript WebSocket Transport

WebSocket transports for the Feedme Javascript Client and Feedme Node.js Server Core libraries.

The server transport runs on Node.js. The client transport runs on Node.js and in the browser.

Created and maintained as a core part of the Feedme project.

• Feedme Javascript WebSocket Transport
  • Server
    • Installation
    • Initialization
    • Usage: Feedme API on a Stand-Alone WebSocket Server
    • Usage: Feedme API on an Existing HTTP/S Server
    • Usage: Multiple Feedme APIs on a Single HTTP/S Server
    • WebSocket Errors
  • Node.js Client
    • Installation
    • Initialization
    • WebSocket Errors
  • Browser Client
    • Installation
    • Initialization
    • WebSocket Errors
  • Compatibility

Server

The server transport lets you serve a Feedme API over WebSockets in Node.js.

The server transport is built on top of the ws module and supports everything that it does, including HTTPS and compression. The transport depends on ws version 6.2.x in order to retain Node 6 support.

Installation

To install the NPM package:

npm install feedme-server-core feedme-transport-ws

Initialization

To initialize a Feedme server:

const feedmeServerCore = require("feedme-server-core");
const feedmeTransportWs = require("feedme-transport-ws/server");

const server = feedmeServerCore({
  transport: feedmeTransportWs(options),
});

The options argument is passed internally to the ws module and can be used to configure the underlying WebSocket server. See the ws documentation for options. The application must not specify the handleProtocols option, which is used internally by the transport.

The transport also incorporates a heartbeat system, which can be confired using:

• options.heartbeatIntervalMs - Optional non-negative integer. Defaults to 5000.

  Specifies how often to send a WebSocket ping to each client to ensure continued responsiveness.

  If set to 0, then the server will not ping clients.

• options.heartbeatTimeoutMs - Optional positive integer. Defaults to 4500.

  Specifies how long to wait after pinging a client until the connection is considered to have been lost and the WebSocket is terminated.

  Must be strictly less than options.heartbeatIntervalMs if specified.

Errors thrown:

• err.message === "INVALID_ARGUMENT"

  There was a problem with one or more of the supplied arguments.

Usage: Feedme API on a Stand-Alone WebSocket Server

To serve a Feedme API on a single-purpose WebSocket server accepting connections on all paths:

const feedmeServerCore = require("feedme-server-core");
const feedmeTransportWs = require("feedme-transport-ws/server");

const server = feedmeServerCore({
  transport: feedmeTransportWs({
    port: 8080,
  }),
});
server.start();

Usage: Feedme API on an Existing HTTP/S Server

To serve a Feedme API on a specific path of an existing HTTP/S server:

const http = require("http");
const feedmeServerCore = require("feedme-server-core");
const feedmeTransportWs = require("feedme-transport-ws/server");

const httpServer = http.createServer(function (req, res) => {
  res.writeHead(200);
  res.end("Welcome");
});
httpServer.listen(8080);

const feedmeServer = feedmeServerCore({
  transport: feedmeTransportWs({
    server: httpServer,
    path: "/feedme"
  })
});
feedmeServer.start();

When serving a Feedme API on an existing HTTP/S server:

• The external HTTP server is not required to be listening in order to initialize the Feedme transport and server. The transport does not attempt to start or stop the external HTTP server.

• If there is a call to feedmeServer.start() and the external HTTP server is not already listening, then feedmeServer will become starting and wait for the HTTP server to be started by the application, at which point feedmeServer will become started. If the HTTP server is already listening when the application calls feedmeServer.start(), then feedmeServer will become started immediately.

• If the external HTTP server stops listening for new connections, either due to a failure or an application call to httpServer.close(), then feedmeServer will automatically become stopped and any existing clients will be disconnected. If the external HTTP server is subsequently restarted then the application must call feedmeServer.start() to re-launch the Feedme server.

• If there is a call to feedmeServer.stop() while the external HTTP server is running then the WebSocket endpoint is removed and the external server is left running.

Usage: Multiple Feedme APIs on a Single HTTP/S Server

To serve multiple Feedme APIs on a single HTTP/S server:

const http = require("http");
const feedmeServerCore = require("feedme-server-core");
const feedmeTransportWs = require("feedme-transport-ws/server");

// Create the basic HTTP server
const httpServer = http.createServer((req, res) => {
  res.writeHead(200);
  res.end("Welcome");
});
httpServer.listen(port);

// Create the first Feedme server
const feedmeTransport1 = feedmeTransportWs({
  noServer: true,
});
const feedmeServer1 = feedmeServerCore({
  transport: feedmeTransport1,
});
feedmeServer1.start();

// Create the second Feedme server
const feedmeTransport2 = feedmeTransportWs({
  noServer: true,
});
const feedmeServer2 = feedmeServerCore({
  transport: feedmeTransport2,
});
feedmeServer2.start();

// Route WebSocket upgrade requests to the appropriate Feedme transport
httpServer.on("upgrade", (request, socket, head) => {
  const { pathname } = url.parse(request.url);
  if (pathname === "/feedme1") {
    feedmeTransport1.handleUpgrade(request, socket, head);
  } else if (pathname === "/feedme2") {
    feedmeTransport2.handleUpgrade(request, socket, head);
  } else {
    socket.destroy();
  }
});

When serving a Feedme API in noServer mode:

• The transport has no way of knowing whether the external HTTP server is listening for connections. It is up to the application to start and stop the Feedme server as appropriate.

• The application must call feedmeServerX.start() before making calls to feedmeTransportX.handleUpgrade(). The Feedme server will immediately become started.

• A call to httpServer.close() will cause the external HTTP server to stop listening for new connections, but it will not terminate existing connections and httpServer will not emit close until all WebSocket clients have disconnected. If the application closes the external HTTP server, it should also call feedmeServerX.stop(), which will cause the transport to close all existing WebSocket connections.

WebSocket Errors

The transport makes the following ws-level error information available to applications via the Feedme server library.

• If there is a problem initializing the ws module then the error thrown by ws is made available to server library stopping and stop event handlers as err.wsError.

• If the ws module or an external HTTP server emits a close event then the associated error is made available to the server library stopping and stop event handlers as err.wsError.

• When a client connection closes unexpectedly, the WebSocket disconnect code and reason are made available to server library disconnect event handlers as err.wsCode and err.wsReason.

• If the ws module calls back an error when attempting to send a message or a ping to a client then the error is made available to server library disconnect event handlers as err.wsError.

Node.js Client

The Node.js client transport lets you connect to a Feedme API server over Webockets from Node.js.

The Node.js client is built on top of the ws module and supports everything it does, including HTTPS and compression. The client depends on ws version 6.2.x in order to retain Node 6 support.

Installation

To install the NPM package:

npm install feedme-transport-ws

Initialization

To initialize a Feedme client:

const feedmeClient = require("feedme-client");
const feedmeTransportWs = require("feedme-transport-ws/client");

const client = feedmeClient({
  transport: feedmeTransportWs(address, options);
});

Transport factory function arguments:

• address - Required string. The server WebSocket URL (ws://...)

• options Optional object. The object is passed to the ws module and can be used to configure the underlying WebSocket client. See the ws documentation for options.

  The Node transport client also incorporates a heartbeat system, which can be configured using:

  • options.heartbeatIntervalMs - Optional non-negative integer. Defaults to 5000.

    Specifies how often to send a WebSocket ping to the server to ensure responsiveness.

    If set to 0, then the client will not ping the server.

  • options.heartbeatTimeoutMs - Optional positive integer. Defaults to 4999.

    Specifies how long to wait after pinging the server until the connection is considered to have been lost.

    Must be strictly less than options.heartbeatIntervalMs if specified.

Errors thrown:

• err.message === "INVALID_ARGUMENT"

  There was a problem with one or more of the supplied arguments.

WebSocket Errors

The transport makes the following ws-level error information available to applications via the Feedme client library.

• If there is a problem initializing the ws module then the error thrown by ws is made available to client library [disconnect]((https://github.com/aarong/feedme-client#disconnect) event handlers as err.wsError.

• If the connection closes unexpectedly, the WebSocket disconnect code and reason are made available to client library disconnect event handlers as err.wsCode and err.wsReason.

• If the ws module calls back an error when attempting to send a message or a ping to the server then the error is made available to client library [disconnect]((https://github.com/aarong/feedme-client#disconnect) event handlers as err.wsError.

Browser Client

The browser client transport lets you connect to a Feedme API server over Webockets using the native WebSocket implementation available in the browser.

Unlike the Node.js client, the browser client does not have a heartbeat feature because browser WebSocket implementations do not expose a ping API. Heartbeat functionality is left to the browser.

Installation

To install the NPM package:

npm install feedme-transport-ws

To access using a CDN:

<script
  type="text/javascript"
  src="https://cdn.jsdelivr.net/npm/feedme-transport-ws"
></script>

The module is named feedmeTransportWs in the global scope.

Initialization

To initialize a Feedme client:

const feedmeClient = require("feedme-client");
const feedmeTransportWs = require("feedme-transport-ws/browser");

const client = feedmeClient({
  transport: feedmeTransportWs(address);
});
client.connect();

Transport factory function arguments:

• address - Required string. The server WebSocket URL.

Errors thrown:

• err.message === "INVALID_ARGUMENT"

  There was a problem with one or more of the supplied arguments.

• err.message === "NO_WEBSOCKETS"

  There is no WebSocket implementation available.

WebSocket Errors

The transport makes the following WebSocket-level error information available to applications via the Feedme client library.

• If an error is thrown when initializing a WebSocket object then the error is made available to client library [disconnect]((https://github.com/aarong/feedme-client#disconnect) event handlers as err.wsError.

• If the connection closes unexpectedly, the WebSocket disconnect code and reason are made available to client library disconnect event handlers as err.wsCode and err.wsReason.

• If an error is thrown when attempting to send a message to the server then the error is made available to client library [disconnect]((https://github.com/aarong/feedme-client#disconnect) event handlers as err.wsError.

Compatibility

The server module should be compatible be with third-party WebSocket client transports that:

1. Specify either no WebSocket subprotocol or a feedme subprotocol.

2. Transmit Feedme messages by sending a single string across the WebSocket.

3. Do not transmit anything else on the WebSocket.

The client module should be compatible with third-party WebSocket server transports that:

1. Accept connections with a feedme WebSocket subprotocol.

2. Transmit Feedme messages by sending a single string across the WebSocket.

3. Do not transmit anything else on the WebSocket.