mTCPJSON

Module with classes to send and receive data as JSON over TCP.

Getting Started

1. Install mTCPJSON via NPM.

npm install mtcpjson

Optionally: rename mtcpjson to mTCPJSON: npm is unable to handle the complexity of uppercase characters in a module name. Node.js on Windows does not have this problem, so renaming the folder is not required for you to use the module.

1. Require mTCPJSON in your project.

var mTCPJSON = require("mTCPJSON");

1. Instantiate a cServer to accept connections and send/receive data.

var oTCPJSONServer = new mTCPJSON.cServer();
oTCPJSONServer.on("connect", fHandleConnection);
function fHandleConnection(oTCPJSONConnection) {
  oTCPJSONConnection.on("message", function (oError, xData) {
    if (oError) {
      // Handle oError
    } else {
      // Process xData
    }
  });
  oTCPJSONConnection.fSendMessage("Anything that can be stringified", function (oError) {
    if (oError) {
      // Failed to send (connection was closed).
    };
  });
};

1. Create a cConnection to a server and send/receive data.

new mTCPJSON.fConnect(fHandleConnection);

(See step 3 above for an example implementation of fHandleConnection).

Notes

A ''client'' instantiates a connection to a ''server'' by calling fConnect and a ''server'' accepts connections from ''clients'' by instantiating a cServer instance. A successfully established connection results in a cConnection instance for both the ''client'' and the ''server''. From that point on, both the ''client'' and ''server'' can send and receive JSON messages as equals.

cConnection.fSendMessage is used to send a message that consist of one value converted to a string using JSON.stringify. cConnection instances emit one message event for each such message received, with two arguments. The first argument is an Error object when an invalid message was received or undefined if the message was valid. If the message was valid, the second argument is the value that was sent, reconstructed from the data in the message using JSON.parse.

Protocol

The protocol used to transmit data is simple and robust. Each message sent starts with a string that represents the length of the JSON data in the message, followed by a semi colon. This is followed by the actual JSON data and another semicolon. Messages that are larger than the maximum transfer unit (MTU) of the network are broken into smaller chunks. However, to reduce the risk of a sender swamping a receiver with data, there is a limit of 1Mb on the size of the JSON data that can be transmitted in one message.

Example:

14;"Hello, World";

Where "Hello, World" is of course 14 characters long. If a message is received that is not in accordance with the protocol, the receiver emits an "error" event.

API

class cServer

Can be used to accept connections, through which you can send values as JSON.

Constructors:

[new] mTCPJSON.cServer([Object dxOptions]);

Where dxOptions is an optional object that can have the following properties:

• Number uIPVersion: IP version to use (valid values: 4 (default), 6).
• String sHostname: Network device to bind to (default: computer name, use localhost if you want to accept connections only from scripts running on the same machine).
• Number uPort: port number to send to (default: 28876).
• Number uConnectionKeepAlive: Enable sending TCP keep-alive packets every uConnectionKeepAlive milliseconds.

Events:

error, parameter: Error oError

Emitted when there is a network error.

start

Emitted when the cServer instance is ready to receive connections.

connect, parameter: cConnection oConnection

Emitted when a connection to the server is established.

stop

Emitted when the cServer instance has stopped receiving connections. This can happen when there is a network error or after you tell the sender to stop.

Methods:

undefined fStop(bDisconnect)

Stop the cServer instance. If bDisconnect is false, the server stops accepting new connections and will wait for existing connections to close. If bDisconnect is true, the server will also disconnect all existing connections. The server will emit a stop event as soon as it no longer accepts new connections and there are no more open connections.

`undefined fConnect(Function fCallback[, Object dxOptions])

Where dxOptions is an optional object that can have the following properties:

• Number uIPVersion: IP version to use (valid values: 4 (default), 6).
• String sHostname: Target computer (default: connect to local computer).
• Number uPort: port number to connect to (default: 28876).
• Number uConnectionKeepAlive: Enable sending TCP keep-alive packets every uConnectionKeepAlive milliseconds. fConnect attempts to establish a connection of a cServer instance using the provided dxOptions. fCallback(Error oError, cConnection oConnection) is called when a connection cannot be established (oError will contain details) or when a connection has been established (oError will be undefined and oConnection will contain a cConnection instance).

class cConnection

Represent connections through which data can be transmitted as JSON messages. Instances of cConnection are emitted through the connect event of cServer instances, and passed to the callback of the fConnect function.

Events:

error, parameter: Error oError

Emitted when there is a network error.

message, parameters: Error oError, Any xData

Emitted when the cConnection instance has received a message. If the message was invalid, oError will contain a description of the problem. Otherwise, oError will be undefined and xData will contain the data sent by the cConnection instance on the other end of the connection.

disconnect

Emitted when the cConnection instance has stopped receiving messages. This happens when there is a network error or after you tell the connection to disconnect.

Methods:

undefined fSendMessage(Any xMessage, Function fCallback)

Convert the data in xMessage to string using JSON.stringify and send it to through the connection. fCallback(Error oError) is called when the message has been sent (oError == undefined) or if there was an error (oError will contain details).

undefined fDisconnect()

Disconnect the cConnection instance.

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License

This code is licensed under CC0 v1.0 Universal.