systemquery/src/lib/agent/PeerServer.mjs

"use strict";

import { EventEmitter, once } from 'events';
import net from 'net';

import p_retry from 'p-retry';
import log from 'log'; const l = log.get("peerserver");

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

import Peer from './Peer.mjs';

/**
 * A server that handles connections to many peers.
 * Note that when a new peer connects it is NOT asked for a list of peers it is
 * aware of. This is something you need to handle yourself!
 * @extends EventEmitter
 */
class PeerServer extends EventEmitter {
	constructor(our_id, secret_join) {
		super();
		
		this.our_id = our_id;
		this.secret_join = secret_join;
		
		// The number of retries when attempting to connect to a peer
		this.retries = 5;
		
		this.connected_peers = [];
		this.connecting_peers = [];
	}
	
	/**
	 * Starts the PeerServer listening on the given port and bind address.
	 * @param	{Number}	[port=5252]		The port number to listen on.
	 * @param	{String}	[host="::"]		The address to bind to.
	 * @return	{Promise<void>}				A Promise that resolves when the server setup is complete.
	 */
	listen(port = 5252, host="::") {
		return new Promise((resolve, reject) => {
			this.server = net.createServer(async (client) => {
				await this.handle_client(client);
			});
			
			this.server.once("error", reject);
			this.server.on("error", this.handle_error);
			this.server.listen({
				host,
				port,
				exclusive: false
			}, () => {
				this.server.off("error", reject);
				resolve();
			});
		});
	}
	
	handle_error(error) {
		throw error;
	}
	
	async handle_client(client) {
		const peer = await Peer.Accept(this, await Connection.Wrap(this.secret_join, client));
		this.peer_initialise(peer);
		await once(peer, "connect");
	}
	
	/**
	 * Initialises a CONNECTED peer and registers it as a valid peer.
	 * This also includesd attaching the necessary event handlers.
	 * @param  {Peer}	peer	The peer in question.
	 * @return {void}
	 */
	peer_initialise(peer) {
		this.connected_peers.push(peer);
		peer.on("message", this.handle_message.bind(this, peer));
		peer.on("destroy", this.handle_destroy.bind(this, peer));
	}
	
	async handle_message(peer, message) {
		this.emit("message", peer, message);
		this.emit(`message-${message.event}`, peer, message.message);
	}
	
	async handle_destroy(peer) {
		const index = this.connected_peers.indexOf(peer);
		if(index > -1)
			this.connected_peers.splice(index, 1);
		
		l.log(`Peer ${peer.address}:${peer.port} disconnected`);
		this.emit("disconnect", peer.remote_endpoint);
	}
	
	/**
	 * Returns a list of all currently known peer addresses.
	 * @return	{{address:string,port:number}[]}
	 */
	peers() {
		return this.connected_peers.map((peer) => peer.remote_endpoint)
			.filter(el => typeof el.addr === "string" && typeof el.port === "number");
	}
	
	/**
	 * Resolves a Peer id to the respective peer instance.
	 * @param	{string|Peer}	peer_id	The peer ID to resolve as a string. If a Peer instance is passed instead, this is simply returned unchanged.
	 * @return	{Peer}		The Peer instance associated with the given peer id.
	 */
	peer_resolve(peer_id) {
		if(peer_id instanceof Peer) return peer_id;
		for (let peer of this.connected_peers) {
			if(peer.id === peer_id) return peer;
		}
	}
	
	/**
	 * Resolves a list of peer ids (and potentially Peer instances) to a list
	 * of Peer instances.
	 * Any Peer instances passed are returned unchanged.
	 * @param	{...string|Peer}	peers	The peer(s) to resolve.
	 * @return	{Peer[]}			A list of Peer instances.
	 */
	peers_resolve(...peers) {
		return peers.map(this.peer_resolve);
	}
	
	/**
	 * Processes a list of peers.
	 * New connections are established to any peers in the list to which
	 * we don't already have a connection.
	 * Note that this function does NOT connect to any other peers known to the
	 * peers in the list you've specified! You need to do this manually.
	 * @param {...{address: string, port: number}} new_peers  The list of new peers to process.
	 * @returns	{Promise<Peer[]>}	A list of new peers to which we have successfully established a connection.
	 */
	async add_peers(...new_peers) {
		// The arrow function here is NOT async because the promise from
		// this.add_peer is returned directly to await Promise.all().
		return (await Promise.all(new_peers.map(
			new_peer => p_retry(async () => await this.add_peer(
				new_peer.address,
				new_peer.port
			), {
				retries: this.retries,
				onFailedAttempt: (error, attempt, left) =>
					l.error(`[attempt ${attempt} / ${left}] Error while connecting to ${new_peer.address}:${new_peer.port}: ${error}`)
			})
		))).filter(peer => peer instanceof Peer);
	}
	
	/**
	 * Connects to a new peer and adds them to the pool of currently connected peers.
	 * Note: This does NOT automatically connect to all the peers known to the
	 * peer you're connecting to!
	 * You need to do this manually.
	 * @throws	{ErrorWrapper}		Throws if the connection failed. This could be for a large number of different reasons, from an incorrect join secret from the remote to connection issues.
	 * @param	{string}	address	The address to connect to.
	 * @param	{number}	port	The port number to connect to.
	 * @return	{Promise<Peer|null>}	A Promise that resolves to the resulting Peer connection, or null if the connection wasn't attemped.
	 */
	async add_peer(address, port) {
		// If we're already connected, don't bother reconnecting again
		if(this.peers().some(el => el.address === address && el.port === port))
			return;
		
		const peer_string = `peer:${address}:${port}`;
		this.connecting_peers.push(peer_string);
		let conn;
		try {
			conn = await Peer.Initiate(this, address, port);
			peer_initialise(conn);
		}
		catch(error) {
			throw new ErrorWrapper(`Error: Failed to connect to peer.`, error);
		}
		finally {
			this.connecting_peers.splice(this.connecting_peers.indexOf(peer_string));
		}
		
		this.emit(`peer`, conn);
		return conn;
	}
	
	/**
	 * Sends a message to 1 or more peers.
	 * @param	{string|Peer|string[]|Peer[]}	peer_id		Either the peer id or the peer itself to which we should send the message. May also be an array of arbitrarily mixed items - in which case the message will be sent to all the specified peers in parallel. The order which peers are messaged is undefined.
	 * @param	{string}		event_name	The name of the event to send.
	 * @param	{Object}		msg			The message itself to send.
	 * @return	{Promise}		A Promise that resolves (or potentially rejects) when the message has been sent.
	 */
	async send(peer_id, event_name, msg) {
		if(!(peer_id instanceof Array)) peer_id = [ peer_id ];
		
		await Promise.all(this.peers_resolve(...peer_id).map(
			peer => peer.send(event_name, msg)
		));
	}
	
	/**
	 * Sends a message in parallel to all peers to which we have an established
	 * connection.
	 * The order which peers are messaged is undefined.
	 * @param	{string}		event_name	The name of the event to send.
	 * @param	{Object}		msg			The message itself to send.
	 * @return	{Promise}		A Promise that resolves (or potentially rejects) when the message has been sent.
	 */
	async broadcast(event_name, msg) {
		await this.send(this.connected_peers, event_name, msg);
	}
	
	/**
	 * Shuts the server down.
	 * This does not disconnect any existing peers!
	 * @return {Promise} A Promise that resolves once the server has been shutdown.
	 */
	shutdown_server() {
		return new Promise((resolve, _reject) => {
			this.server.close(resolve);
		});
	}
	
	/**
	 * Stops the PeerServer and gracefully (if possible) disconnects all existing peers.
	 * @return	{Promise}	A Promise that resolves once the shutdown process has completed.
	 */
	async destroy() {
		await this.shutdown_server();
		await Promise.all(...this.connected_peers.map(peer => peer.destroy()));
	}
}

export default PeerServer;