ll-protocol

Node.js custom TCP protocol

Characteristics

• Send multiple messages at the same time on the same socket
• listen to a type of message by adding a event listener
• Allow streaming of messages
• Message body can be raw bytes
• protocol is written with es2015 (es6) syntax

Usage

Server

const net = require("net");
const fs = require("fs");
const LLProtocol = require("ll-protocol");

server = new net.Server();

server.on("connection", (socket) => {
    let protocol = new LLProtocol(socket);

    // accept a file
    protocol.on("someFile", (request) => {
    	const filename = request.headers.filename;

    	const writer = fs.createWriteStream(filename);

    	request.pipe(writer);
    });


    // send a basic string message ('makeResponse' already calls 'send' for response)
    const response = protocol.makeResponse('someMessage', 'This is some content to send');

});

server.listen(8000);

Client

const net = require("net");
const fs = require("fs");
const LLProtocol = require("ll-protocol");

const StringRequest = LLProtocol.request.StringRequest;

const client = new net.Socket();

client.connect(8000, () => {
    const protocol = new LLProtocol(client);

    // accept a basic string message
    protocol.setReader('someMessage', StringRequest);

    protocol.on("someMessage", (content) => {
    	console.log("someMessage event fired with content:", content);
    });


    // Send a file
    const filename = "thisissomecoolfilename.txt";
    const reader = fs.createReadStream(filename);

    const response = new LLProtocol.Response({ type: 'someFile', filename });

    reader.pipe(response);

    protocol.send(response);

});

Protocol

Message

---------------------------
|      Header (json)      |
| { type: 'messageType' } |
---------------------------
|      HEADERSEQUENCE     |
---------------------------
|      Message Content    |
|      (raw bytes)        |
---------------------------

Frame

When a message is streamed to the protocol, all chunks get into its own frame. A frameheader and frame sequence are added to the frame.

---------------------------
|  Frameheader (9 bytes)  |
---------------------------
|      Frame Content      |
|      (raw bytes)        |
---------------------------
|      FRAMESEQUENCE      |
---------------------------

Frameheader

------------------------------
|    Message Id (4 bytes)    |
------------------------------
|    Frame index (4 bytes)   |
------------------------------
| Last frame (bool) (1 byte) |
------------------------------

HEADERSEQUENCE and FRAMESEQUENCE

The sequences are both an array of bytes. The numbers are a decimal representation of the byte value (min: 0, max 255)

LLProtocol.config.SEQUENCES.header = [ 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0 ];
LLProtocol.config.SEQUENCES.frame = [ 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 ];

Because the sequences are the same for 10 bytes, when going through the chunks, it only need to check once every 10 bytes. This makes it a lot faster.