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63 lines
2.1 KiB
JavaScript
63 lines
2.1 KiB
JavaScript
8 months ago
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"use strict";
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Object.defineProperty(exports, "__esModule", { value: true });
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exports.SlipEncoder = void 0;
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const stream_1 = 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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*
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* 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.
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*/
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class SlipEncoder extends stream_1.Transform {
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constructor(options = {}) {
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super(options);
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const { START, ESC = 0xdb, END = 0xc0, ESC_START, ESC_END = 0xdc, ESC_ESC = 0xdd, bluetoothQuirk = false } = options;
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this.opts = {
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START,
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ESC,
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END,
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ESC_START,
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ESC_END,
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ESC_ESC,
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bluetoothQuirk,
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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.opts.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.opts.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 && this.opts.ESC_START) {
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encoded[j++] = this.opts.ESC;
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byte = this.opts.ESC_START;
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}
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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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}
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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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exports.SlipEncoder = SlipEncoder;
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