@skybloxsystems/ticket-bot
Version:
227 lines (211 loc) • 7.27 kB
JavaScript
const { Transform } = require('stream');
/**
* Base class for WebmOpusDemuxer and WebmVorbisDemuxer.
* **You shouldn't directly instantiate this class, use the opus.WebmDemuxer and vorbis.WebmDemuxer
* implementations instead!**
* @memberof core
* @protected
* @extends TransformStream
*/
class WebmBaseDemuxer extends Transform {
/**
* Creates a new Webm demuxer.
* @private
* @memberof core
* @param {Object} [options] options that you would pass to a regular Transform stream.
*/
constructor(options = {}) {
super(Object.assign({ readableObjectMode: true }, options));
this._remainder = null;
this._length = 0;
this._count = 0;
this._skipUntil = null;
this._track = null;
this._incompleteTrack = {};
this._ebmlFound = false;
}
_transform(chunk, encoding, done) {
this._length += chunk.length;
if (this._remainder) {
chunk = Buffer.concat([this._remainder, chunk]);
this._remainder = null;
}
let offset = 0;
if (this._skipUntil && this._length > this._skipUntil) {
offset = this._skipUntil - this._count;
this._skipUntil = null;
} else if (this._skipUntil) {
this._count += chunk.length;
done();
return;
}
let result;
while (result !== TOO_SHORT) {
try {
result = this._readTag(chunk, offset);
} catch (error) {
done(error);
return;
}
if (result === TOO_SHORT) break;
if (result._skipUntil) {
this._skipUntil = result._skipUntil;
break;
}
if (result.offset) offset = result.offset;
else break;
}
this._count += offset;
this._remainder = chunk.slice(offset);
done();
return;
}
/**
* Reads an EBML ID from a buffer.
* @private
* @param {Buffer} chunk the buffer to read from.
* @param {number} offset the offset in the buffer.
* @returns {Object|Symbol} contains an `id` property (buffer) and the new `offset` (number).
* Returns the TOO_SHORT symbol if the data wasn't big enough to facilitate the request.
*/
_readEBMLId(chunk, offset) {
const idLength = vintLength(chunk, offset);
if (idLength === TOO_SHORT) return TOO_SHORT;
return {
id: chunk.slice(offset, offset + idLength),
offset: offset + idLength,
};
}
/**
* Reads a size variable-integer to calculate the length of the data of a tag.
* @private
* @param {Buffer} chunk the buffer to read from.
* @param {number} offset the offset in the buffer.
* @returns {Object|Symbol} contains property `offset` (number), `dataLength` (number) and `sizeLength` (number).
* Returns the TOO_SHORT symbol if the data wasn't big enough to facilitate the request.
*/
_readTagDataSize(chunk, offset) {
const sizeLength = vintLength(chunk, offset);
if (sizeLength === TOO_SHORT) return TOO_SHORT;
const dataLength = expandVint(chunk, offset, offset + sizeLength);
return { offset: offset + sizeLength, dataLength, sizeLength };
}
/**
* Takes a buffer and attempts to read and process a tag.
* @private
* @param {Buffer} chunk the buffer to read from.
* @param {number} offset the offset in the buffer.
* @returns {Object|Symbol} contains the new `offset` (number) and optionally the `_skipUntil` property,
* indicating that the stream should ignore any data until a certain length is reached.
* Returns the TOO_SHORT symbol if the data wasn't big enough to facilitate the request.
*/
_readTag(chunk, offset) {
const idData = this._readEBMLId(chunk, offset);
if (idData === TOO_SHORT) return TOO_SHORT;
const ebmlID = idData.id.toString('hex');
if (!this._ebmlFound) {
if (ebmlID === '1a45dfa3') this._ebmlFound = true;
else throw Error('Did not find the EBML tag at the start of the stream');
}
offset = idData.offset;
const sizeData = this._readTagDataSize(chunk, offset);
if (sizeData === TOO_SHORT) return TOO_SHORT;
const { dataLength } = sizeData;
offset = sizeData.offset;
// If this tag isn't useful, tell the stream to stop processing data until the tag ends
if (typeof TAGS[ebmlID] === 'undefined') {
if (chunk.length > offset + dataLength) {
return { offset: offset + dataLength };
}
return { offset, _skipUntil: this._count + offset + dataLength };
}
const tagHasChildren = TAGS[ebmlID];
if (tagHasChildren) {
return { offset };
}
if (offset + dataLength > chunk.length) return TOO_SHORT;
const data = chunk.slice(offset, offset + dataLength);
if (!this._track) {
if (ebmlID === 'ae') this._incompleteTrack = {};
if (ebmlID === 'd7') this._incompleteTrack.number = data[0];
if (ebmlID === '83') this._incompleteTrack.type = data[0];
if (this._incompleteTrack.type === 2 && typeof this._incompleteTrack.number !== 'undefined') {
this._track = this._incompleteTrack;
}
}
if (ebmlID === '63a2') {
this._checkHead(data);
this.emit('head', data);
} else if (ebmlID === 'a3') {
if (!this._track) throw Error('No audio track in this webm!');
if ((data[0] & 0xF) === this._track.number) {
this.push(data.slice(4));
}
}
return { offset: offset + dataLength };
}
_destroy(err, cb) {
this._cleanup();
return cb ? cb(err) : undefined;
}
_final(cb) {
this._cleanup();
cb();
}
/**
* Cleans up the demuxer when it is no longer required.
* @private
*/
_cleanup() {
this._remainder = null;
this._incompleteTrack = {};
}
}
/**
* A symbol that is returned by some functions that indicates the buffer it has been provided is not large enough
* to facilitate a request.
* @name WebmBaseDemuxer#TOO_SHORT
* @memberof core
* @private
* @type {Symbol}
*/
const TOO_SHORT = WebmBaseDemuxer.TOO_SHORT = Symbol('TOO_SHORT');
/**
* A map that takes a value of an EBML ID in hex string form, with the value being a boolean that indicates whether
* this tag has children.
* @name WebmBaseDemuxer#TAGS
* @memberof core
* @private
* @type {Object}
*/
const TAGS = WebmBaseDemuxer.TAGS = { // value is true if the element has children
'1a45dfa3': true, // EBML
'18538067': true, // Segment
'1f43b675': true, // Cluster
'1654ae6b': true, // Tracks
'ae': true, // TrackEntry
'd7': false, // TrackNumber
'83': false, // TrackType
'a3': false, // SimpleBlock
'63a2': false,
};
module.exports = WebmBaseDemuxer;
function vintLength(buffer, index) {
let i = 0;
for (; i < 8; i++) if ((1 << (7 - i)) & buffer[index]) break;
i++;
if (index + i > buffer.length) {
return TOO_SHORT;
}
return i;
}
function expandVint(buffer, start, end) {
const length = vintLength(buffer, start);
if (end > buffer.length || length === TOO_SHORT) return TOO_SHORT;
let mask = (1 << (8 - length)) - 1;
let value = buffer[start] & mask;
for (let i = start + 1; i < end; i++) {
value = (value << 8) + buffer[i];
}
return value;
}