webm-duration-fix/src/ebml/EBMLDecoder.ts

based on ts-ebml and support large file(than 2GB) and optimize memory usage during repair

import {Int64BE} from "int64-buffer";
import {Buffer, readVint, convertEBMLDateToJSDate} from "./tools";
import * as EBML from "./EBML";
import * as tools from "./tools";
import { byEbmlID } from "./ebmlID";

enum State {
  STATE_TAG = 1,
  STATE_SIZE = 2,
  STATE_CONTENT = 3
}

export default class EBMLDecoder {

  private _buffer: Buffer;
  private _tag_stack: EBML.EBMLElementDetail[];
  private _state: State;
  /**
   * _buffer の先頭からの位置
   */
  private _cursor: number;
  /**
   * 全体におけるポインタ
   */
  private _total: number;
  private _schema: typeof byEbmlID;
  private _result: EBML.EBMLElementDetail[];

  constructor() {
    this._buffer = new Buffer(0);
    this._tag_stack = [];
    this._state = State.STATE_TAG;
    this._cursor = 0;
    this._total = 0;
    this._schema = byEbmlID;
    this._result = [];
  }

  decode(chunk: ArrayBuffer): EBML.EBMLElementDetail[] {
    this.readChunk(chunk);
    const diff = this._result;
    this._result = [];
    return diff;
  }

  private readChunk(chunk: ArrayBuffer): void {
    // 読みかけの(読めなかった) this._buffer と 新しい chunk を合わせて読み直す
    this._buffer = tools.concat([this._buffer, new Buffer(chunk)]);
    while (this._cursor < this._buffer.length) {
      // console.log(this._cursor, this._total, this._tag_stack);
      if(this._state === State.STATE_TAG && !this.readTag()) { break; }
      if(this._state === State.STATE_SIZE && !this.readSize()) { break; }
      if(this._state === State.STATE_CONTENT && !this.readContent()) { break; }
    }
  }

  private getSchemaInfo(tagNum: number): EBML.Schema {
    return this._schema[tagNum] || {
      name: "unknown",
      level: -1,
      type: "unknown",
      description: "unknown"
    };
  }

  /**
   * vint された parsing tag
   * @return - return false when waiting for more data
   */
  private readTag(): boolean {
    // tag.length が buffer の外にある
    if(this._cursor >= this._buffer.length) { return false; }

    // read ebml id vint without first byte
    const tag = readVint(this._buffer, this._cursor);

    // tag が読めなかった
    if (tag == null) { return false; }

    // >>>>>>>>>
    // tag 識別子
    //const tagStr = this._buffer.toString("hex", this._cursor, this._cursor + tag.length);
    //const tagNum = parseInt(tagStr, 16);
    // 上と等価
    const buf = this._buffer.slice(this._cursor, this._cursor + tag.length);
    const tagNum = buf.reduce((o, v, i, arr)=> o + v * Math.pow(16, 2*(arr.length-1-i)), 0);

    const schema = this.getSchemaInfo(tagNum);
    
    const tagObj: EBML.EBMLElementDetail = <any>{
        EBML_ID: tagNum.toString(16),
        schema,
        type: schema.type,
        name: schema.name,
        level: schema.level,
        tagStart: this._total,
        tagEnd: this._total + tag.length,
        sizeStart: this._total + tag.length,
        sizeEnd: null,
        dataStart: null,
        dataEnd: null,
        dataSize: null,
        data: null
    };
    // | tag: vint | size: vint | data: Buffer(size) |

    this._tag_stack.push(tagObj);
    // <<<<<<<<

    // ポインタを進める
    this._cursor += tag.length;
    this._total += tag.length;

    // 読み込み状態変更
    this._state = State.STATE_SIZE;
    
    return true;
  }

  /**
   * vint された現在のタグの内容の大きさを読み込む
   * @return - return false when waiting for more data
   */
  private readSize(): boolean {
      // tag.length が buffer の外にある
    if (this._cursor >= this._buffer.length) { return false; }

    // read ebml datasize vint without first byte
    const size = readVint(this._buffer, this._cursor);

    // まだ読めない
    if (size == null) { return false; }

    // >>>>>>>>>
    // current tag の data size 決定
    const tagObj = this._tag_stack[this._tag_stack.length - 1];

    tagObj.sizeEnd = tagObj.sizeStart + size.length;

    tagObj.dataStart = tagObj.sizeEnd;

    tagObj.dataSize = size.value;

    if (size.value === -1) {
      // unknown size
      tagObj.dataEnd = -1;
      if(tagObj.type === "m"){
        tagObj.unknownSize = true;
      }
    } else {
      tagObj.dataEnd = tagObj.sizeEnd + size.value;
    }
    
    // <<<<<<<<

    // ポインタを進める
    this._cursor += size.length;
    this._total += size.length;

    this._state = State.STATE_CONTENT;

    return true;
  }

  /**
   * データ読み込み
   */
  private readContent(): boolean {

    const tagObj = this._tag_stack[this._tag_stack.length - 1];
    
    // master element は子要素を持つので生データはない
    if (tagObj.type === 'm') {
      // console.log('content should be tags');
      tagObj.isEnd = false;
      this._result.push(tagObj);
      this._state = State.STATE_TAG;
      // この Mastert Element は空要素か
      if(tagObj.dataSize === 0){
        // 即座に終了タグを追加
        const elm = Object.assign({}, tagObj, {isEnd: true});
        this._result.push(elm);
        this._tag_stack.pop(); // スタックからこのタグを捨てる
      }
      return true;
    }

    // waiting for more data
    if (this._buffer.length < this._cursor + tagObj.dataSize) { return false; }

    // タグの中身の生データ
    const data = this._buffer.slice(this._cursor, this._cursor + tagObj.dataSize);
    
    // 読み終わったバッファを捨てて読み込んでいる部分のバッファのみ残す
    this._buffer = this._buffer.slice(this._cursor + tagObj.dataSize);

    tagObj.data = data;

    // >>>>>>>>>
    switch(tagObj.type){
      //case "m": break;
        // Master-Element - contains other EBML sub-elements of the next lower level
      case "u": tagObj.value = data.readUIntBE(0, data.length); break;
        // Unsigned Integer - Big-endian, any size from 1 to 8 octets
      case "i": tagObj.value = data.readIntBE(0, data.length); break;
        // Signed Integer - Big-endian, any size from 1 to 8 octets
      case "f": tagObj.value = tagObj.dataSize === 4 ? data.readFloatBE(0) :
                               tagObj.dataSize === 8 ? data.readDoubleBE(0) :
                               (console.warn(`cannot read ${tagObj.dataSize} octets float. failback to 0`), 0); break;
        // Float - Big-endian, defined for 4 and 8 octets (32, 64 bits)
      case "s": tagObj.value = data.toString("ascii"); break; // ascii
        //  Printable ASCII (0x20 to 0x7E), zero-padded when needed
      case "8": tagObj.value = data.toString("utf8"); break;
        //  Unicode string, zero padded when needed (RFC 2279)
      case "b": tagObj.value = data; break;
        // Binary - not interpreted by the parser
      case "d": tagObj.value = convertEBMLDateToJSDate(new Int64BE(data).toNumber()); break;
        // nano second; Date.UTC(2001,1,1,0,0,0,0) === 980985600000
        // Date - signed 8 octets integer in nanoseconds with 0 indicating 
        // the precise beginning of the millennium (at 2001-01-01T00:00:00,000000000 UTC)
    }
    if(tagObj.value === null){
      throw new Error("unknown tag type:" + tagObj.type);
    }
    this._result.push(tagObj);

    // <<<<<<<<

    // ポインタを進める
    this._total += tagObj.dataSize;

    // タグ待ちモードに変更
    this._state = State.STATE_TAG;
    this._cursor = 0;
    this._tag_stack.pop(); // remove the object from the stack

    while (this._tag_stack.length > 0) {
      const topEle = this._tag_stack[this._tag_stack.length - 1];
      // 親が不定長サイズなので閉じタグは期待できない
      if(topEle.dataEnd < 0){
        this._tag_stack.pop(); // 親タグを捨てる
        return true;
      }
      // 閉じタグの来るべき場所まで来たかどうか
      if (this._total < topEle.dataEnd) {
          break;
      }
      // 閉じタグを挿入すべきタイミングが来た
      if(topEle.type !== "m"){ throw new Error("parent element is not master element"); }
      const elm = Object.assign({}, topEle, {isEnd: true});
      this._result.push(elm);
      this._tag_stack.pop();
    }

    return true;
  }
}