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feat: Add slip decoder to parser-slip-encoder (#2196)
- Add option to specify slip escape codes - Add optional start and start escape
1 parent 015bc17 commit 85297bc

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4 files changed

+402
-74
lines changed

4 files changed

+402
-74
lines changed

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

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const { Transform } = require('stream')
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/**
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* A transform stream that decodes slip encoded data.
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* @extends Transform
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* @summary Runs in O(n) time, stripping out slip encoding and emitting decoded data. Optionally,
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* custom slip escape and delimiters can be provided.
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* @example
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// Receive slip encoded data from a serialport and log decoded data
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const SerialPort = require('serialport')
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const { SlipDecoder } = require('@serialport/parser-slip-encoder')
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const port = new SerialPort('/dev/tty-usbserial1')
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const parser = port.pipe(new SlipDecoder())
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parser.on('data', console.log)
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*/
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class SlipDecoder extends Transform {
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constructor(options = {}) {
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super(options)
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const opts = {
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START: undefined,
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ESC: 0xdb,
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END: 0xc0,
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ESC_START: undefined,
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ESC_END: 0xdc,
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ESC_ESC: 0xdd,
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...options,
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}
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this.opts = opts
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this.buffer = Buffer.alloc(0)
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this.escape = false
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this.start = false
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}
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_transform(chunk, encoding, cb) {
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for (let ndx = 0; ndx < chunk.length; ndx++) {
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let byte = chunk[ndx]
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if (byte === this.opts.START) {
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this.start = true
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continue
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} else if (undefined == this.opts.START) {
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this.start = true
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}
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if (this.escape) {
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if (byte === this.opts.ESC_START) {
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byte = this.opts.START
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} else if (byte === this.opts.ESC_ESC) {
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byte = this.opts.ESC
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} else if (byte === this.opts.ESC_END) {
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byte = this.opts.END
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} else {
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this.escape = false
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this.push(this.buffer)
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this.buffer = Buffer.alloc(0)
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}
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} else {
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if (byte === this.opts.ESC) {
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this.escape = true
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continue
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}
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if (byte === this.opts.END) {
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this.push(this.buffer)
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this.buffer = Buffer.alloc(0)
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this.escape = false
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this.start = false
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continue
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}
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}
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this.escape = false
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if (true === this.start) {
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this.buffer = Buffer.concat([this.buffer, Buffer.from([byte])])
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}
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}
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cb()
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}
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_flush(cb) {
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this.push(this.buffer)
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this.buffer = Buffer.alloc(0)
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cb()
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}
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}
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module.exports = SlipDecoder

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

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const { Transform } = require('stream')
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/**
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* A transform stream that emits SLIP-encoded data for each incoming packet.
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* @extends Transform
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* @summary Runs in O(n) time, adding a 0xC0 character at the end of each
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* received packet and escaping characters, according to RFC 1055. Adds another
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* 0xC0 character at the beginning if the `bluetoothQuirk` option is truthy (as
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* per the Bluetooth Core Specification 4.0, Volume 4, Part D, Chapter 3 "SLIP Layer").
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* Optionally, custom slip escape and delimiters can be provided.
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* @example
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// Read lines from a text file, then SLIP-encode each and send them to a serial port
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const SerialPort = require('serialport')
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const { SlipEncoder } = require('@serialport/parser-slip-encoder')
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const Readline = require('parser-readline')
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const fileReader = require('fs').createReadStream('/tmp/some-file.txt');
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const port = new SerialPort('/dev/tty-usbserial1')
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const lineParser = fileReader.pipe(new Readline({ delimiter: '\r\n' }));
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const encoder = fileReader.pipe(new SlipEncoder({ bluetoothQuirk: false }));
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encoder.pipe(port);
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*/
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class SlipEncoder extends Transform {
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constructor(options = {}) {
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super(options)
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const opts = {
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START: undefined,
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ESC: 0xdb,
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END: 0xc0,
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ESC_START: undefined,
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ESC_END: 0xdc,
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ESC_ESC: 0xdd,
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...options,
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}
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this.opts = opts
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if (options.bluetoothQuirk) {
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this._bluetoothQuirk = true
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}
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}
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_transform(chunk, encoding, cb) {
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const chunkLength = chunk.length
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if (this._bluetoothQuirk && chunkLength === 0) {
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// Edge case: push no data. Bluetooth-quirky SLIP parsers don't like
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// lots of 0xC0s together.
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return cb()
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}
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// Allocate memory for the worst-case scenario: all bytes are escaped,
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// plus start and end separators.
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const encoded = Buffer.alloc(chunkLength * 2 + 2)
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let j = 0
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if (this._bluetoothQuirk == true) {
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encoded[j++] = this.opts.END
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}
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if (this.opts.START !== undefined) {
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encoded[j++] = this.opts.START
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}
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for (let i = 0; i < chunkLength; i++) {
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let byte = chunk[i]
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if (byte === this.opts.START) {
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encoded[j++] = this.opts.ESC
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byte = this.opts.ESC_START
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} else if (byte === this.opts.END) {
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encoded[j++] = this.opts.ESC
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byte = this.opts.ESC_END
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} else if (byte === this.opts.ESC) {
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encoded[j++] = this.opts.ESC
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byte = this.opts.ESC_ESC
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}
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encoded[j++] = byte
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}
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encoded[j++] = this.opts.END
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cb(null, encoded.slice(0, j))
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}
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}
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module.exports = SlipEncoder

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

Lines changed: 3 additions & 72 deletions
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const { Transform } = require('stream')
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const END = 0xc0
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const ESC = 0xdb
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const ESC_END = 0xdc
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const ESC_ESC = 0xdd
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/**
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* A transform stream that emits SLIP-encoded data for each incoming packet.
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* @extends Transform
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* @summary Runs in O(n) time, adding a 0xC0 character at the end of each
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* received packet and escaping characters, according to RFC 1055. Adds another
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* 0xC0 character at the beginning if the `bluetoothQuirk` option is truthy (as
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* per the Bluetooth Core Specification 4.0, Volume 4, Part D, Chapter 3 "SLIP Layer").
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* Runs in O(n) time.
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* @example
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// Read lines from a text file, then SLIP-encode each and send them to a serial port
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const SerialPort = require('serialport')
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const SlipEncoder = require('@serialport/parser-slip-encoder')
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const Readline = require('parser-readline')
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const fileReader = require('fs').createReadStream('/tmp/some-file.txt');
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const port = new SerialPort('/dev/tty-usbserial1')
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const lineParser = fileReader.pipe(new Readline({ delimiter: '\r\n' }));
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const encoder = fileReader.pipe(new SlipEncoder({ bluetoothQuirk: false }));
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encoder.pipe(port);
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*/
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class SlipEncoderParser extends Transform {
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constructor(options = {}) {
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super(options)
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if (options.bluetoothQuirk) {
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this._bluetoothQuirk = true
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}
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}
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_transform(chunk, encoding, cb) {
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const chunkLength = chunk.length
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if (this._bluetoothQuirk && chunkLength === 0) {
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// Edge case: push no data. Bluetooth-quirky SLIP parsers don't like
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// lots of 0xC0s together.
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return cb()
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}
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// Allocate memory for the worst-case scenario: all bytes are escaped,
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// plus start and end separators.
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const encoded = Buffer.alloc(chunkLength * 2 + 2)
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let j = 0
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if (this._bluetoothQuirk) {
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encoded[j++] = END
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}
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for (let i = 0; i < chunkLength; i++) {
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let byte = chunk[i]
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if (byte === END) {
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encoded[j++] = ESC
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byte = ESC_END
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} else if (byte === ESC) {
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encoded[j++] = ESC
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byte = ESC_ESC
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}
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encoded[j++] = byte
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}
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encoded[j++] = END
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cb(null, encoded.slice(0, j))
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}
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module.exports = {
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SlipEncoder: require('./encoder'),
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SlipDecoder: require('./decoder'),
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}
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module.exports = SlipEncoderParser

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