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112 lines
3.0 KiB
JavaScript
112 lines
3.0 KiB
JavaScript
// Tweaked version of nathan7's binary-parse-stream
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// (see https://github.com/nathan7/binary-parse-stream)
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// Uses NoFilter instead of the readable in the original. Removes
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// the ability to read -1, which was odd and un-needed.
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// License for binary-parse-stream: MIT
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// binary-parse-stream is now unmaintained, so I have rewritten it as
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// more modern JS so I can get tsc to help check types.
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'use strict';
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// eslint-disable-next-line n/prefer-node-protocol
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const stream = require('stream');
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const NoFilter = require('nofilter');
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/**
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* BinaryParseStream is a TransformStream that consumes buffers and outputs
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* objects on the other end. It expects your subclass to implement a `_parse`
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* method that is a generator. When your generator yields a number, it'll be
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* fed a buffer of that length from the input. When your generator returns,
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* the return value will be pushed to the output side.
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*
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* @extends stream.Transform
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*/
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class BinaryParseStream extends stream.Transform {
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/**
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* Creates an instance of BinaryParseStream.
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*
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* @memberof BinaryParseStream
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* @param {stream.TransformOptions} options Stream options.
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*/
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constructor(options) {
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super(options);
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// Doesn't work to pass these in as opts, for some reason
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// also, work around typescript not knowing TransformStream internals
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// eslint-disable-next-line dot-notation
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this['_writableState'].objectMode = false;
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// eslint-disable-next-line dot-notation
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this['_readableState'].objectMode = true;
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this.bs = new NoFilter();
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this.__restart();
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}
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/**
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* Transforming.
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*
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* @param {any} fresh Buffer to transcode.
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* @param {BufferEncoding} _encoding Name of encoding.
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* @param {stream.TransformCallback} cb Callback when done.
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* @ignore
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*/
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_transform(fresh, _encoding, cb) {
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this.bs.write(fresh);
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while (this.bs.length >= this.__needed) {
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let ret = null;
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const chunk = (this.__needed === null) ?
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undefined :
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this.bs.read(this.__needed);
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try {
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ret = this.__parser.next(chunk);
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} catch (e) {
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return cb(e);
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}
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if (this.__needed) {
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this.__fresh = false;
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}
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if (ret.done) {
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this.push(ret.value);
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this.__restart();
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} else {
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this.__needed = ret.value || Infinity;
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}
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}
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return cb();
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}
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/**
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* Subclasses must override this to set their parsing behavior. Yield a
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* number to receive a Buffer of that many bytes.
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*
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* @abstract
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* @returns {Generator<number, any, Buffer>}
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*/
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/* istanbul ignore next */
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*_parse() { // eslint-disable-line class-methods-use-this, require-yield
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throw new Error('Must be implemented in subclass');
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}
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__restart() {
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this.__needed = null;
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this.__parser = this._parse();
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this.__fresh = true;
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}
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/**
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* Flushing.
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*
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* @param {stream.TransformCallback} cb Callback when done.
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* @ignore
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*/
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_flush(cb) {
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cb(this.__fresh ? null : new Error('unexpected end of input'));
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}
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}
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module.exports = BinaryParseStream;
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