initial

relay.mjs

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+import readline from 'node:readline';
+import net from 'node:net';
+import fs from 'node:fs';
+
+
+export class Relay {
+
+	#target_stream = null;
+	#socket_server = null;
+	#line_buffer_tally = 0;
+
+	constructor(listening_socket, target_socket, line_buffer=[], line_buffer_max_size=1024**2) {
+		Object.assign(this, { listening_socket, target_socket, line_buffer, line_buffer_max_size });
+	}
+	serve() {
+
+		const server = net.createServer((socket) => {
+
+			console.log("socket connected");
+
+			const rli = readline.createInterface({
+				input: socket,
+				crlfDelay: Infinity
+			});
+
+			rli.on('line', (line) => this.log_line(line));
+
+			socket.on('close', () => {
+				console.log("socket closed");
+			});
+
+			socket.on('error', (err) => {
+				console.log("socket error", { err });
+			});
+
+		});
+
+
+		server.on('error', (err) => {
+			console.log("server error", { err });
+		});
+
+		this.listening_socket.listen(server, () => {
+			this.#socket_server = server;
+		});
+
+	}
+
+	buffer_line(line) {
+
+		this.#line_buffer_tally += line.length + 1;
+		this.line_buffer.push(line);	// NOTE: We may of course briefly overshoot here but we are not expecting or caring about huge oneliners for now
+
+		while (this.line_buffer.length && (this.#line_buffer_tally > this.line_buffer_max_size)) {
+			const discarded = this.line_buffer.shift();
+			this.#line_buffer_tally -= discarded.length + 1;
+			console.log({ discarded });
+		}
+
+	}
+
+	log_line(line) {
+		this.buffer_line(line);
+
+		if (this.#target_stream) {
+			this.#flush();
+		} else {
+			this.#connect_target();
+		}
+
+	}
+
+	#connect_target() {
+
+		if (this.#target_stream) {
+			return;
+		}
+
+		const socket = net.createConnection(this.target_socket.connect_options);
+
+		socket.on('connect', () => {
+			this.#target_stream = socket;
+			this.#flush();
+		});
+
+		socket.on('error', (err) => {
+			console.log("target error", { err });
+			socket.destroy();
+			this.#target_stream = null;
+		});
+
+		socket.on('close', () => {
+			this.#target_stream = null;
+		});
+
+	}
+
+
+	#flush() {
+
+		while (this.line_buffer.length && this.#target_stream) {
+
+			const line = this.line_buffer[0];
+			const ok = this.#target_stream.write(line + '\n');
+
+			if (ok === false) {
+				return;
+			}
+
+			this.line_buffer.shift();
+		}
+	}
+
+
+
+}