const Transform = require('stream').Transform;
/**
* Emit data every number of bytes
* @extends Transform
* @param {Object} options parser options object
* @param {Number} options.length the number of bytes on each data event
* @summary A transform stream that emits data as a buffer after a specific number of bytes are received. Runs in O(n) time.
* @example
const SerialPort = require('serialport')
const ByteLength = require('@serialport/parser-byte-length')
const port = new SerialPort('/dev/tty-usbserial1')
const parser = port.pipe(new ByteLength({length: 8}))
parser.on('data', console.log) // will have 8 bytes per data event
*/
class ByteLengthParser extends Transform {
constructor(options) {
super(options);
options = options || {};
if (typeof options.length !== 'number') {
throw new TypeError('"length" is not a number');
}
if (options.length < 1) {
throw new TypeError('"length" is not greater than 0');
}
this.length = options.length;
this.position = 0;
this.buffer = Buffer.alloc(this.length);
}
_transform(chunk, encoding, cb) {
let cursor = 0;
while (cursor < chunk.length) {
this.buffer[this.position] = chunk[cursor];
cursor++;
this.position++;
if (this.position === this.length) {
this.push(this.buffer);
this.buffer = Buffer.alloc(this.length);
this.position = 0;
}
}
cb();
}
_flush(cb) {
this.push(this.buffer.slice(0, this.position));
this.buffer = Buffer.alloc(this.length);
cb();
}
}
module.exports = ByteLengthParser;