feat: Add slip decoder to parser-slip-encoder (#2196)

- Add option to specify slip escape codes
- Add optional start and start escape

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

@@ -0,0 +1,94 @@
+const { Transform } = require('stream')
+
+/**
+* A transform stream that decodes slip encoded data.
+* @extends Transform
+* @summary Runs in O(n) time, stripping out slip encoding and emitting decoded data. Optionally,
+* custom slip escape and delimiters can be provided.
+* @example
+// Receive slip encoded data from a serialport and log decoded data
+const SerialPort = require('serialport')
+const { SlipDecoder } = require('@serialport/parser-slip-encoder')
+const port = new SerialPort('/dev/tty-usbserial1')
+const parser = port.pipe(new SlipDecoder())
+parser.on('data', console.log)
+*/
+class SlipDecoder extends Transform {
+  constructor(options = {}) {
+    super(options)
+
+    const opts = {
+      START: undefined,
+      ESC: 0xdb,
+      END: 0xc0,
+
+      ESC_START: undefined,
+      ESC_END: 0xdc,
+      ESC_ESC: 0xdd,
+
+      ...options,
+    }
+    this.opts = opts
+
+    this.buffer = Buffer.alloc(0)
+    this.escape = false
+    this.start = false
+  }
+
+  _transform(chunk, encoding, cb) {
+    for (let ndx = 0; ndx < chunk.length; ndx++) {
+      let byte = chunk[ndx]
+
+      if (byte === this.opts.START) {
+        this.start = true
+        continue
+      } else if (undefined == this.opts.START) {
+        this.start = true
+      }
+
+      if (this.escape) {
+        if (byte === this.opts.ESC_START) {
+          byte = this.opts.START
+        } else if (byte === this.opts.ESC_ESC) {
+          byte = this.opts.ESC
+        } else if (byte === this.opts.ESC_END) {
+          byte = this.opts.END
+        } else {
+          this.escape = false
+          this.push(this.buffer)
+          this.buffer = Buffer.alloc(0)
+        }
+      } else {
+        if (byte === this.opts.ESC) {
+          this.escape = true
+          continue
+        }
+
+        if (byte === this.opts.END) {
+          this.push(this.buffer)
+          this.buffer = Buffer.alloc(0)
+
+          this.escape = false
+          this.start = false
+          continue
+        }
+      }
+
+      this.escape = false
+
+      if (true === this.start) {
+        this.buffer = Buffer.concat([this.buffer, Buffer.from([byte])])
+      }
+    }
+
+    cb()
+  }
+
+  _flush(cb) {
+    this.push(this.buffer)
+    this.buffer = Buffer.alloc(0)
+    cb()
+  }
+}
+
+module.exports = SlipDecoder

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

@@ -0,0 +1,89 @@
+const { Transform } = require('stream')
+
+/**
+* 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").
+* Optionally, custom slip escape and delimiters can be provided.
+* @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('@serialport/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 SlipEncoder extends Transform {
+  constructor(options = {}) {
+    super(options)
+
+    const opts = {
+      START: undefined,
+      ESC: 0xdb,
+      END: 0xc0,
+
+      ESC_START: undefined,
+      ESC_END: 0xdc,
+      ESC_ESC: 0xdd,
+
+      ...options,
+    }
+    this.opts = opts
+
+    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.
+    const encoded = Buffer.alloc(chunkLength * 2 + 2)
+    let j = 0
+
+    if (this._bluetoothQuirk == true) {
+      encoded[j++] = this.opts.END
+    }
+
+    if (this.opts.START !== undefined) {
+      encoded[j++] = this.opts.START
+    }
+
+    for (let i = 0; i < chunkLength; i++) {
+      let byte = chunk[i]
+
+      if (byte === this.opts.START) {
+        encoded[j++] = this.opts.ESC
+        byte = this.opts.ESC_START
+      } else if (byte === this.opts.END) {
+        encoded[j++] = this.opts.ESC
+        byte = this.opts.ESC_END
+      } else if (byte === this.opts.ESC) {
+        encoded[j++] = this.opts.ESC
+        byte = this.opts.ESC_ESC
+      }
+
+      encoded[j++] = byte
+    }
+
+    encoded[j++] = this.opts.END
+
+    cb(null, encoded.slice(0, j))
+  }
+}
+
+module.exports = SlipEncoder

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

@@ -1,73 +1,4 @@
-const { Transform } = require('stream')
-
-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('@serialport/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 = {}) {
-    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.
-    const 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 = {
+  SlipEncoder: require('./encoder'),
+  SlipDecoder: require('./decoder'),
 }
-
-module.exports = SlipEncoderParser