126 lines
4 KiB
JavaScript
126 lines
4 KiB
JavaScript
"use strict";
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import os from 'os';
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import log from 'log';
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const l = log.get("framedtransport");
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import { EventEmitter, once } from 'events';
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import { write_safe, end_safe } from '../io/StreamHelpers.mjs';
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/**
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* Manages a TCP socket using a simple binary frame system.
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* Frames look like this:
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*
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* <LENGTH: Uint32 big-endian> <DATA: Uint8Array>
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*/
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class FramedTransport extends EventEmitter {
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constructor(socket) {
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super();
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this.socket = socket;
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this.socket.on("data", this.handle_chunk.bind(this));
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this.buffer = null;
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/** The length of a uint in bytes @type {number} */
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this.uint_length = 4;
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this.writing = false;
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}
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/**
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* Handles a single chunk of incoming data.
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* May or may not emit a frame event.
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* @param {Buffer|TypedArray} chunk The incoming chunk of data.
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* @return {void}
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*/
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handle_chunk(chunk) {
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l.debug(`CHUNK length`, chunk.length, `buffer length`, this.buffer === null ? 0 : this.buffer.length);
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if(this.buffer instanceof Buffer) {
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this.buffer = Buffer.concat([ this.buffer, chunk ]);
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}
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else
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this.buffer = chunk;
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l.debug(`CHUNK buffer`, this.buffer);
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let next_frame_length = this.buffer2uint(this.buffer, 0);
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l.debug(`CHUNK total length`, this.buffer.length, `next_frame_length`, next_frame_length);
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// We have enough data! Emit a frame and then start again.
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if(this.buffer.length - this.uint_length >= next_frame_length) {
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this.emit("frame", this.buffer.slice(this.uint_length, next_frame_length));
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if(this.buffer.length - (this.uint_length + next_frame_length) > 0)
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this.buffer = this.buffer.slice(this.uint_length + next_frame_length);
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else
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this.buffer = null;
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l.info(`FRAME length`, next_frame_length, `length_remaining`, this.buffer === null ? 0 : this.buffer.length);
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}
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}
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/**
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* Converts the number at a given position in a buffer from Uint32 with
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* big-endian encoding to a normal number.
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* @param {Buffer|TypedArray} buffer The source buffer.
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* @param {number} pos32 The position in the buffer to read from.
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* @return {number} The parsed number from the buffer.
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*/
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buffer2uint(buffer, pos32) {
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l.debug(`BUFFER2UINT buffer`, buffer, `pos32`, pos32);
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// DataView doesn't work as expected here, because Node.js optimises small buffer to be views of 1 larger buffer.
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let u8 = new Uint8Array(buffer).slice(pos32, this.uint_length);
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// Convert from network byte order if necessary
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if(os.endianness() == "LE") u8.reverse();
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l.debug(`BUFFER2UINT u8`, u8, `u32`, new Uint32Array(u8.buffer));
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return new Uint32Array(u8.buffer)[0];
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}
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/**
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* Converts a positive integer into a Buffer using big-endian encoding.
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* @param {number} uint The positive integer to convert.
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* @return {Buffer} A new buffer representing the given number.
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*/
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uint2buffer(uint) {
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// DataView doesn't work as expected here, because Node.js optimises small buffer to be views of 1 larger buffer.
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let array = new ArrayBuffer(this.uint_length);
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const u8 = new Uint8Array(array);
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const u32 = new Uint32Array(array);
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u32[0] = uint;
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// Host to network byte order, if appropriate
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if(os.endianness() == "LE") u8.reverse();
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return Buffer.from(array);
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}
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/**
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* Writes a given Buffer or TypedArray to the underlying socket inn a new frame.
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* @param {Buffer|TypedArray} frame The data to send in a new frame.
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* @return {Promise} A promise that resolves when writing is complete.
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*/
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async write(frame) {
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if(this.writing) await once(this, "write-end");
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this.emit("write-start");
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this.writing = true;
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l.info(`SEND length`, frame.length);
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await write_safe(this.socket, this.uint2buffer(frame.length));
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await write_safe(this.socket, frame);
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this.writing = false;
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this.emit("write-end")
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}
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/**
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* Gracefulls closes this socket.
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* @return {Promise} A Promise that resolves when the socket is properly closed.
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*/
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async destroy() {
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// Calling socket.end() is important as it closes the stream properly
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await end_safe(this.socket);
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await this.socket.destroy();
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}
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}
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export default FramedTransport;
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