systemquery/src/lib/agent/Peer.mjs

"use strict";

import { EventEmitter, once } from 'events';

import log from '../io/NamespacedLog.mjs'; const l = log("peer");

import Connection from '../transport/Connection.mjs';

class Peer extends EventEmitter {
	get address() { return this.connection.address; }
	get port() { return this.connection.port; }
	get remote_endpoint() {
		return { address: this.address, port: this.port };
	}
	get id_short() {
		if(this.id === null) return null;
		return this.id.substring(0, 7);
	}
	
	get info() {
		return {
			address: this.address,
			port: this.port,
			id: this.id,
			listening_address: this.listening_address,
			listening_port: this.listening_port
		};
	}
	
	constructor(server, connection) {
		super();
		
		this.id = null;
		
		/**
		 * The parent server this Peer is part of.
		 * @type {PeerServer}
		 */
		this.server = server;
		/**
		 * The underlying Connection.
		 * @type {Connection}
		 */
		this.connection = connection;
		
		// If a message with the event name "end" is received, close our side
		// of the connection
		this.once(`message-end`, this.destroy);
	}
	
	///////////////////////////////////////////////////////////////////////////
	
	/**
	 * Accepts an existing connection as a new Peer.
	 * @param	{Connection}	connection	The Connection to accept.
	 * @return	{Promise<HelloMsg>}	A Promise that resolves once the initial handshake is complete.
	 */
	async __accept(connection) {
		this.connection = connection;
		const [ msg ] = await once(this.connection, "message-hello");
		if(!this.__handle_hello(msg))
			await this.destroy();
		
		await this.__send_hello();
		this.emit("connect");
	}
	
	/**
	 * Initiates the handshake after opening a new connection.
	 * @return	{Promise<HelloMsg>}	A Promise that resolves after the initial peer handshake is complete.
	 */
	__initiate() {
		return new Promise((resolve, reject) => {
			this.connection.once("error", reject);
			this.connection.once("message-hello", async (msg) => {
				if(!this.__handle_hello(msg))
					await this.destroy();
				
				this.connection.off("error", reject);
				this.emit("connect");
				resolve();
			});
			this.__send_hello(); // Set and forget
		});
	}
	
	/**
	 * Handles a given hello messaage from this peer.
	 * @param	{Object}	msg		The hello message to process.
	 * @return	{boolean}	Whether the peer should stay connected or not.
	 */
	__handle_hello(msg) {
		this.id = msg.id;
		this.listening_address = msg.listening_address;
		this.listening_port = msg.listening_port;
		
		if(this.id === this.server.our_id) {
			l.warn(`Our id (${this.server.our_id}) is equal to that of the remote (${this.id}), killing connection`);
			return false;
		}
		
		this.connection.on("message", this.__handle_message.bind(this));
		return true;
	}
	
	__handle_message(event_name, msg) {
		this.emit("message", event_name, msg);
		this.emit(`message-${event_name}`, msg);
	}
	
	/**
	 * Sends a hello message to this peer.
	 * @return {Promise}	A Promise that resolves when the sending of the message is complete.
	 */
	async __send_hello() {
		await this.send("hello", {
			id: this.server.our_id,
			listening_address: this.server.host,
			listening_port: this.server.port
		});
	}
	
	/**
	 * Sends a message to this peer.
	 * @param	{string}	event_name	The event name to attach to the message.
	 * @param	{Object}	msg			The message to send. Can be of any type, but an Object is recommended for increased flexibility later down the line.
	 * @return	{Promise}	A Promise that resolves whent he message has been sent.
	 */
	async send(event_name, msg) {
		await this.connection.send(event_name, msg);
	}
	
	///////////////////////////////////////////////////////////////////////////
	
	/**
	 * Closes the connection to this peer.
	 * Once called, in order to reinstate the connection it's best to
	 * instantiate a new Peer class instance.
	 * @return	{Promise}	A Promise that resolves once the connection is closed.
	 */
	async destroy() {
		// TODO: If sending an end message takes too long, we should just ignore it and move on
		await this.send("end", "goodbye");
		await this.connection.destroy();
		this.emit("destroy");
		this.removeAllListeners();
	}
}

Peer.Initiate = async function(server, address, port) {
	const conn = await Connection.Create(server.secret_join, address, port);
	const peer = new Peer(server, conn);
	await peer.__initiate();
	return peer;
}

Peer.Accept = async function(server, connection) {
	const peer = new Peer(server);
	await peer.__accept(connection);
	
	return peer;
}

export default Peer;