ByteStream.ts

/*---------------------------------------------------------------------------------------------
* Copyright (c) Bentley Systems, Incorporated. All rights reserved.
* See LICENSE.md in the project root for license terms and full copyright notice.
*--------------------------------------------------------------------------------------------*/
/** @packageDocumentation
 * @module Utils
 */

import { assert } from "./Assert";
import { Id64, Id64String } from "./Id";

/** Allows the contents of an [ArrayBuffer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
 * to be consumed sequentially using methods to extract
 * data of a particular type from the bytes beginning at the current read position.
 * Methods and properties beginning with 'read' and taking no arguments consume data at the current read position and advance it
 * by the size of the data read. The read position can also be directly adjusted by the caller.
 * @public
 */
export class ByteStream {
  private readonly _view: DataView;
  private readonly _byteOffset: number;
  private _curPos: number = 0;

  /** Construct a new ByteStream with the read position set to the beginning.
   * @param buffer The underlying buffer from which data is to be extracted.
   * @param subView If defined, specifies the subset of the underlying buffer's data to use.
   * This constructor is subject to two common mistakes:
   *
   * 1. Given `bytes: Uint8Array`, `new ByteStream(bytes)` will compile but at run-time will produce an error asserting that
   * the DataView constructor requires an ArrayBuffer. The correct usage is `new ByteStream(bytes.buffer)`.
   * 2. Given `bytes: Uint8Array`, `new ByteStream(bytes.buffer)` creates a stream for the entire range of bytes represented by the underlying
   * ArrayBuffer. If `bytes` represents only a **sub-range** of the underlying buffer's data, the results will be unexpected unless the optional `subView`
   * argument is supplied, with correct offset and length.
   *
   * For both of the above reasons, prefer to use [[fromUint8Array]].
   * @deprecated in 3.x. Use [[fromUint8Array]] or [[fromArrayBuffer]].
   */
  public constructor(buffer: ArrayBuffer | SharedArrayBuffer, subView?: { byteOffset: number, byteLength: number }) {
    if (undefined !== subView) {
      this._view = new DataView(buffer, subView.byteOffset, subView.byteLength);
      this._byteOffset = subView.byteOffset;
    } else {
      this._view = new DataView(buffer);
      this._byteOffset = 0;
    }
  }

  /** Construct a new ByteStream for the range of bytes represented by `bytes`, which may be a subset of the range of bytes
   * represented by the underlying ArrayBuffer. The read position will be set to the beginning of the range of bytes.
   */
  public static fromUint8Array(bytes: Uint8Array): ByteStream {
    const { byteOffset, byteLength } = bytes;
    return new ByteStream(bytes.buffer, { byteOffset, byteLength }); // eslint-disable-line deprecation/deprecation
  }

  /** Construct a new ByteStream with the read position set to the beginning.
   * @param buffer The underlying buffer from which data is to be extracted.
   * @param subView If defined, specifies the subset of the underlying buffer's data to use.
   */
  public static fromArrayBuffer(buffer: ArrayBuffer | SharedArrayBuffer, subView?: { byteOffset: number, byteLength: number }): ByteStream {
    return new ByteStream(buffer, subView); // eslint-disable-line deprecation/deprecation
  }

  /** The number of bytes in this stream */
  public get length(): number {
    return this._view.byteLength;
  }

  /** The number of bytes remaining to be read, from [[curPos]] to the end of the stream. */
  public get remainingLength(): number {
    return this.length - this.curPos;
  }

  /** Returns true if the current read position has been advanced past the end of the stream. This generally indicates that an attempt was made to read more data than is available.
   * @see [[isAtTheEnd]]
   */
  public get isPastTheEnd(): boolean {
    return this.curPos > this.length;
  }

  /** Returns true if the current read position has advanced precisely to the end of the stream, indicating all of the data has been consumed.
   * @see [[isPastTheEnd]].
   */
  public get isAtTheEnd(): boolean {
    return this.curPos === this.length;
  }

  /** The current read position as an index into the stream of bytes. */
  public get curPos(): number { return this._curPos; }
  public set curPos(pos: number) {
    this._curPos = pos;
    assert(!this.isPastTheEnd);
  }

  /** Adds the specified number of bytes to the current read position */
  public advance(numBytes: number): boolean {
    this.curPos = (this.curPos + numBytes);
    return !this.isPastTheEnd;
  }

  /** Subtracts the specified number of bytes from the current read position */
  public rewind(numBytes: number): boolean {
    if (this.curPos - numBytes < 0)
      return false;

    this.curPos = this.curPos - numBytes;
    return true;
  }

  /** Resets the current read position to the beginning of the stream */
  public reset(): void { this.curPos = 0; }

  /** Read a unsigned 8-bit integer from the current read position and advance by 1 byte. */
  public readUint8(): number { return this.read(1, (view) => view.getUint8(this.curPos)); }
  /** Read an unsigned 16-bit integer from the current read position and advance by 2 bytes. */
  public readUint16(): number { return this.read(2, (view) => view.getUint16(this.curPos, true)); }
  /** Read an unsigned 32-bit integer from the current read position and advance by 4 bytes. */
  public readUint32(): number { return this.read(4, (view) => view.getUint32(this.curPos, true)); }
  /** Read a signed 32-bit integer from the current read position and advance by 4 bytes. */
  public readInt32(): number { return this.read(4, (view) => view.getInt32(this.curPos, true)); }
  /** Read a 32-bit floating point number from the current read position and advance by 4 bytes. */
  public readFloat32(): number { return this.read(4, (view) => view.getFloat32(this.curPos, true)); }
  /** Read a 64-bit floating point number from the current read position and advance by 8 bytes. */
  public readFloat64(): number { return this.read(8, (view) => view.getFloat64(this.curPos, true)); }
  /** Read an unsigned 64-bit integer from the current read position, advance by 8 bytes, and return the 64-bit value as an Id64String. */
  public readId64(): Id64String { return Id64.fromUint32Pair(this.readUint32(), this.readUint32()); }
  /** Read an unsigned 24-bit integer from the current read position and advance by 3 bytes. */
  public readUint24(): number { return this.readUint8() | (this.readUint8() << 8) | (this.readUint8() << 16); }

  /** @deprecated in 3.x. use [[readUint8]]. */
  public get nextUint8(): number { return this.readUint8(); }
  /** @deprecated in 3.x. use [[readUint16]]. */
  public get nextUint16(): number { return this.readUint16(); }
  /** @deprecated in 3.x. use [[readUint32]]. */
  public get nextUint32(): number { return this.readUint32(); }
  /** @deprecated in 3.x. use [[readInt32]]. */
  public get nextInt32(): number { return this.readInt32(); }
  /** @deprecated in 3.x. use [[readFloat32]]. */
  public get nextFloat32(): number { return this.readFloat32(); }
  /** @deprecated in 3.x. use [[readFloat64]]. */
  public get nextFloat64(): number { return this.readFloat64(); }
  /** @deprecated in 3.x. use [[readId64]]. */
  public get nextId64(): Id64String { return this.readId64(); }
  /** @deprecated in 3.x. use [[readUint32]]. */
  public get nextUint24(): number { return this.readUint24(); }

  /** Read the specified number of bytes beginning at the current read position into a Uint8Array and advance by the specified number of byte.
   * @param numBytes The number of bytes to read.
   */
  public nextBytes(numBytes: number): Uint8Array {
    const bytes = new Uint8Array(this.arrayBuffer, this.curPos + this._byteOffset, numBytes);
    this.advance(numBytes);
    return bytes;
  }

  /** Read the specified number of bytes at the specified offset without changing the read position. */
  public readBytes(readPos: number, numBytes: number): Uint8Array {
    return new Uint8Array(this.arrayBuffer, readPos + this._byteOffset, numBytes);
  }

  /** Read the specified number of unsigned 32-bit integers from the current read position and advance the read position. */
  public nextUint32s(numUint32s: number): Uint32Array {
    const numBytes = numUint32s * 4;
    const uint32s = new Uint32Array(this.arrayBuffer, this.curPos + this._byteOffset, numUint32s);
    this.advance(numBytes);
    return uint32s;
  }

  /** Returns the underlying array buffer */
  public get arrayBuffer(): ArrayBuffer | SharedArrayBuffer { return this._view.buffer; }

  private read(numBytes: number, read: (view: DataView) => number) {
    const result = read(this._view);
    this.advance(numBytes);
    return result;
  }
}