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59 lines
2.2 KiB
JavaScript
59 lines
2.2 KiB
JavaScript
"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.PacketLengthParser = void 0;
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const stream_1 = require("stream");
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/**
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* A transform stream that decodes packets with a delimiter and length of payload
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* specified within the data stream.
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* @extends Transform
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* @summary Decodes packets of the general form:
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* [delimiter][len][payload0] ... [payload0 + len]
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*
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* The length field can be up to 4 bytes and can be at any offset within the packet
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* [delimiter][header0][header1][len0][len1[payload0] ... [payload0 + len]
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*
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* The offset and number of bytes of the length field need to be provided in options
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* if not 1 byte immediately following the delimiter.
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*/
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class PacketLengthParser extends stream_1.Transform {
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constructor(options = {}) {
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super(options);
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const { delimiter = 0xaa, packetOverhead = 2, lengthBytes = 1, lengthOffset = 1, maxLen = 0xff } = options;
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this.opts = {
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delimiter,
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packetOverhead,
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lengthBytes,
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lengthOffset,
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maxLen,
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};
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this.buffer = Buffer.alloc(0);
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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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const byte = chunk[ndx];
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if (byte === this.opts.delimiter) {
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this.start = true;
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}
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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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if (this.buffer.length >= this.opts.lengthOffset + this.opts.lengthBytes) {
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const len = this.buffer.readUIntLE(this.opts.lengthOffset, this.opts.lengthBytes);
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if (this.buffer.length == len + this.opts.packetOverhead || len > this.opts.maxLen) {
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this.push(this.buffer);
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this.buffer = Buffer.alloc(0);
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this.start = false;
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}
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}
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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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exports.PacketLengthParser = PacketLengthParser;
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