Adds a SLIP encoder

packages/parser-slip-encoder/README.md

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+See our api docs https://node-serialport.github.io/parsers/SlipEncoderParser.html

packages/parser-slip-encoder/package.json

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+{
+  "name": "parser-slip-encoder",
+  "main": "slip-encoder.js",
+  "version": "1.0.2",
+  "dependencies": {
+    "safe-buffer": "^5.1.1"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/node-serialport/parsers.git"
+  }
+}

packages/parser-slip-encoder/slip-encoder.js

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+'use strict'
+const Buffer = require('safe-buffer').Buffer
+const Transform = require('stream').Transform
+
+const END = 0xC0;
+const ESC = 0xDB;
+const ESC_END = 0xDC;
+const ESC_ESC = 0xDD;
+
+/**
+* A transform stream that emits SLIP-encoded data for each incoming packet.
+* @extends Transform
+* @summary Runs in O(n) time, adding a 0xC0 character at the end of each
+* received packet and escaping characters, according to RFC 1055. Adds another
+* 0xC0 character at the beginning if the `bluetoothQuirk` option is truthy (as
+* per the Bluetooth Core Specification 4.0, Volume 4, Part D, Chapter 3 "SLIP Layer").
+* Runs in O(n) time.
+* @example
+// Read lines from a text file, then SLIP-encode each and send them to a serial port
+const SerialPort = require('serialport')
+const SlipEncoder = require('parser-slip-encoder')
+const Readline = require('parser-readline')
+const fileReader = require('fs').createReadStream('/tmp/some-file.txt');
+const port = new SerialPort('/dev/tty-usbserial1')
+const lineParser = fileReader.pipe(new Readline({ delimiter: '\r\n' }));
+const encoder = fileReader.pipe(new SlipEncoder({ bluetoothQuirk: false }));
+encoder.pipe(port);
+*/
+class SlipEncoderParser extends Transform {
+	constructor (options) {
+		options = options || {}
+		super(options)
+
+		if (options.bluetoothQuirk) {
+			this._bluetoothQuirk = true;
+		}
+	}
+
+	_transform (chunk, encoding, cb) {
+		const chunkLength = chunk.length;
+
+		if (this._bluetoothQuirk && chunkLength === 0) {
+			// Edge case: push no data. Bluetooth-quirky SLIP parsers don't like
+			// lots of 0xC0s together.
+			return cb();
+		}
+
+		// Allocate memory for the worst-case scenario: all bytes are escaped,
+		// plus start and end separators.
+		let encoded = Buffer.alloc((chunkLength * 2) + 2);
+		let j = 0;
+
+		if (this._bluetoothQuirk) {
+			encoded[j++] = END;
+		}
+
+		for (let i=0; i<chunkLength; i++) {
+			let byte = chunk[i];
+			if (byte === END) {
+				encoded[j++] = ESC;
+				byte = ESC_END;
+			} else if (byte === ESC) {
+				encoded[j++] = ESC;
+				byte = ESC_ESC;
+			}
+
+			encoded[j++] = byte;
+		}
+
+		encoded[j++] = END;
+
+		cb(null, encoded.slice(0, j));
+	}
+}
+
+module.exports = SlipEncoderParser

packages/parser-slip-encoder/slip-encoder.test.js

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+'use strict'
+/* eslint-disable no-new */
+
+const Buffer = require('safe-buffer').Buffer
+const sinon = require('sinon')
+
+const SlipEncoder = require('./slip-encoder')
+
+describe('SlipEncoderParser', () => {
+
+	it ('Adds one delimiter to one-byte messages', ()=>{
+		const spy = sinon.spy()
+		const encoder = new SlipEncoder();
+		encoder.on('data', spy);
+
+		encoder.write(Buffer.from([0x01]));
+		encoder.write(Buffer.from([0x80]));
+		encoder.write(Buffer.from([0xFF]));
+		encoder.write(Buffer.from([0xA5]));
+
+		assert.equal(spy.callCount, 4);
+		assert.deepEqual(spy.getCall(0).args[0], Buffer.from([0x01, 0xC0]));
+		assert.deepEqual(spy.getCall(1).args[0], Buffer.from([0x80, 0xC0]));
+		assert.deepEqual(spy.getCall(2).args[0], Buffer.from([0xFF, 0xC0]));
+		assert.deepEqual(spy.getCall(3).args[0], Buffer.from([0xA5, 0xC0]));
+	});
+
+	it ('Adds two delimiters to one-byte messages with the bluetooth quirk', ()=>{
+		const spy = sinon.spy()
+		const encoder = new SlipEncoder({ bluetoothQuirk: true });
+		encoder.on('data', spy);
+
+		encoder.write(Buffer.from([0x01]));
+		encoder.write(Buffer.from([0x80]));
+		encoder.write(Buffer.from([0xFF]));
+		encoder.write(Buffer.from([0xA5]));
+
+		assert.equal(spy.callCount, 4);
+		assert.deepEqual(spy.getCall(0).args[0], Buffer.from([0xC0, 0x01, 0xC0]));
+		assert.deepEqual(spy.getCall(1).args[0], Buffer.from([0xC0, 0x80, 0xC0]));
+		assert.deepEqual(spy.getCall(2).args[0], Buffer.from([0xC0, 0xFF, 0xC0]));
+		assert.deepEqual(spy.getCall(3).args[0], Buffer.from([0xC0, 0xA5, 0xC0]));
+	});
+
+	it ('Adds one delimiter to zero-byte messages', ()=>{
+		const spy = sinon.spy()
+		const encoder = new SlipEncoder();
+		encoder.on('data', spy);
+
+		encoder.write(Buffer.from([]));
+
+		assert.equal(spy.callCount, 1);
+		assert.deepEqual(spy.getCall(0).args[0], Buffer.from([0xC0]));
+	});
+
+	it ('Does nothing with zero-byte messages with the bluetooth quirk', ()=>{
+		const spy = sinon.spy()
+
+		const encoder = new SlipEncoder({ bluetoothQuirk: true });
+
+		encoder.on('data', spy);
+
+		encoder.write(Buffer.from([]));
+		encoder.write(Buffer.from([]));
+		encoder.write(Buffer.from([]));
+		encoder.write(Buffer.from([]));
+
+		assert.equal(spy.callCount, 0);
+	});
+
+
+	it ('Escapes characters', ()=>{
+		const spy = sinon.spy()
+		const encoder = new SlipEncoder();
+		encoder.on('data', spy);
+
+		encoder.write(Buffer.from([0x01]));
+		encoder.write(Buffer.from([0xC0]));
+		encoder.write(Buffer.from([0xDB]));
+		encoder.write(Buffer.from([0xDC]));
+		encoder.write(Buffer.from([0xDD]));
+		encoder.write(Buffer.from([0xFF]));
+
+		assert.equal(spy.callCount, 6);
+		assert.deepEqual(spy.getCall(0).args[0], Buffer.from([0x01, 0xC0]));
+		assert.deepEqual(spy.getCall(1).args[0], Buffer.from([0xDB, 0xDC, 0xC0]));
+		assert.deepEqual(spy.getCall(2).args[0], Buffer.from([0xDB, 0xDD, 0xC0]));
+		assert.deepEqual(spy.getCall(3).args[0], Buffer.from([0xDC, 0xC0]));
+		assert.deepEqual(spy.getCall(4).args[0], Buffer.from([0xDD, 0xC0]));
+		assert.deepEqual(spy.getCall(5).args[0], Buffer.from([0xFF, 0xC0]));
+	});
+
+	it ('Escapes characters with the bluetooth quirk', ()=>{
+		const spy = sinon.spy()
+		const encoder = new SlipEncoder({ bluetoothQuirk: true });
+		encoder.on('data', spy);
+
+		encoder.write(Buffer.from([0x01]));
+		encoder.write(Buffer.from([0xC0]));
+		encoder.write(Buffer.from([0xDB]));
+		encoder.write(Buffer.from([0xDC]));
+		encoder.write(Buffer.from([0xDD]));
+		encoder.write(Buffer.from([0xFF]));
+
+		assert.equal(spy.callCount, 6);
+		assert.deepEqual(spy.getCall(0).args[0], Buffer.from([0xC0, 0x01, 0xC0]));
+		assert.deepEqual(spy.getCall(1).args[0], Buffer.from([0xC0, 0xDB, 0xDC, 0xC0]));
+		assert.deepEqual(spy.getCall(2).args[0], Buffer.from([0xC0, 0xDB, 0xDD, 0xC0]));
+		assert.deepEqual(spy.getCall(3).args[0], Buffer.from([0xC0, 0xDC, 0xC0]));
+		assert.deepEqual(spy.getCall(4).args[0], Buffer.from([0xC0, 0xDD, 0xC0]));
+		assert.deepEqual(spy.getCall(5).args[0], Buffer.from([0xC0, 0xFF, 0xC0]));
+	});
+});