@kleppe/litematic-reader/lib/data_view_stream.ts

Example: ```ts import { readFile } from "fs/promises"; import { Litematic } from '@kleppe/litematic-reader'

import { DefaultEndianDataView } from "./default_endian_data_view";

const decoder = new TextDecoder("utf-8");
const encoder = new TextEncoder();

/**
 * Parses utf8 encoded text to a JS string
 * 
 * @param array The data to decode
 * @param i The start index
 * @param length The length
 * @returns a JS string
 */
export function decodeUtf8(array: DataView, i: number, length: number): string {
  if (length === 0) { return ''; }
  return decoder.decode(new DataView(array.buffer, array.byteOffset + i, length));
}

/**
 * Encodes the given string as utf8.
 * 
 * @param s The string
 * @returns The utf8 encoding as a Uint8Array
 */
export function encodeUtf8Into(s: string, array: DataView, i: number): number {
  const { written } = encoder.encodeInto(s, new Uint8Array(array.buffer, array.byteOffset + i));
  if (written == null) { throw new Error(`Encoding string failed: '${s}'`); }
  return written;
}

/**
 * Streams data to a DataView.
 * Each writer method moves the cursor forward,
 * and resizing is automatic.
 */
export class DataViewWriter {
  i = 0;
  data: DefaultEndianDataView;
  constructor(initialCapacity = 1024, readonly littleEndian = false) {
    this.data = new DefaultEndianDataView(littleEndian, new ArrayBuffer(initialCapacity));
  }

  byte(n: number) {
    this.assertCapacity(1);
    this.data.setInt8(this.i, n);
    this.i++;
  }

  short(n: number) {
    this.assertCapacity(2);
    this.data.setInt16(this.i, n);
    this.i += 2;
  }

  int(n: number) {
    this.assertCapacity(4);
    this.data.setInt32(this.i, n);
    this.i += 4;
  }

  long(n: bigint) {
    this.assertCapacity(8);
    this.data.setBigInt64(this.i, n);
    this.i += 8;
  }

  float(n: number) {
    this.assertCapacity(4);
    this.data.setFloat32(this.i, n);
    this.i += 4;
  }

  double(n: number) {
    this.assertCapacity(8);
    this.data.setFloat64(this.i, n);
    this.i += 8;
  }

  string(s: string) {
    // 1 utf-16 character or unpaired surrogate may
    // become up to 3 bytes of utf-8. Reserve enough space
    this.assertCapacity(s.length * 3);
    const written = encodeUtf8Into(s, this.data, this.i + 2);
    this.data.setUint16(this.i, written);
    this.i += written + 2;
  }

  array(array: DataView, width: number) {
    const nItems = Math.floor(array.byteLength / width);
    this.assertCapacity(array.byteLength + 4);
    this.data.setInt32(this.i, nItems);
    this.i += 4;
    // we can just copy byte-by-byte, since both buffers
    // are big-endian. Use Uint8Arrays to represent the ranges.
    new Uint8Array(this.data.buffer, this.i, array.byteLength)
      .set(new Uint8Array(array.buffer, array.byteOffset, array.byteLength));

    this.i += array.byteLength;
  }

  varint(value: number) {
    if (value < 0x80) {
      this.byte(value & 0x7f);
    } else if (value < 0x4000) {
      this.byte(0x80 | value & 0x7f);
      this.byte(((value & 0x3f80) >>> 7));
    } else if (value < 0x200000) {
      this.byte(0x80 | value & 0x7f);
      this.byte(0x80 | ((value & 0x3f80) >>> 7));
      this.byte(((value & 0x1fc000) >>> 14));
    } else if (value < 0x10000000) {
      this.byte(0x80 | value & 0x7f);
      this.byte(0x80 | ((value & 0x3f80) >>> 7));
      this.byte(0x80 | ((value & 0x1fc000) >>> 14));
      this.byte(((value & 0xfe00000) >>> 21));
    } else {
      this.byte(0x80 | value & 0x7f);
      this.byte(0x80 | ((value & 0x3f80) >>> 7));
      this.byte(0x80 | ((value & 0x1fc000) >>> 14));
      this.byte(0x80 | ((value & 0xfe00000) >>> 21));
      this.byte(((value & 0xF0000000) >>> 28));
    }
  }

  zigZagVarint(value: number) {
    this.varint((value << 1) ^ (value >> 31));
  }

  final(): DefaultEndianDataView {
    return this.data.subview(0, this.i);
  }

  /**
   * Assures that the internal buffer can hold newBytes extra
   * bytes, doubling the current buffer size as necessary.
   * @param newBytes The number of new bytes to add
   */
  private assertCapacity(newBytes: number) {
    if (this.i + newBytes > this.data.byteLength) {
      let newSize = this.data.byteLength * 2;
      while (this.i + newBytes > newSize) {
        newSize *= 2;
      }
      const newData = new DefaultEndianDataView(this.littleEndian, new ArrayBuffer(newSize));
      new Uint8Array(newData.buffer).set(new Uint8Array(this.data.buffer));
      this.data = newData;
    }
  }
}

/**
 * Streams data from a DataView.
 * Each accessor method moves the cursor forward,
 * consuming the data.
 */
export class DataViewReader {
  i = 0;
  constructor(readonly data: DefaultEndianDataView) {
  }

  byte(): number {
    this.i += 1;
    return this.data.getInt8(this.i - 1);
  }

  short(): number {
    this.i += 2;
    return this.data.getInt16(this.i - 2);
  }

  int(): number {
    this.i += 4;
    return this.data.getInt32(this.i - 4);
  }

  long(): bigint {
    this.i += 8;
    return this.data.getBigInt64(this.i - 8);
  }

  string(): string {
    const length = this.data.getUint16(this.i);
    this.i += 2;
    const string = decodeUtf8(this.data, this.i, length);
    this.i += length;
    return string;
  }

  float(): number {
    this.i += 4;
    return this.data.getFloat32(this.i - 4);
  }

  double(): number {
    this.i += 8;
    return this.data.getFloat64(this.i - 8);
  }

  array(width: number): DataView {
    const length = this.int();
    const result = this.data.subview(this.i, length * width);
    this.i += result.byteLength;
    return result;
  }

  varint(): number {
    let first4 = this.data.getUint32(this.i, true);
    let result = first4 & 0x7f;
    this.i++;

    for (let shift = 7; shift < 28 && (first4 & 0x80) !== 0; shift += 7) {
      first4 = first4 >>> 8;
      result |= (first4 & 0x7f) << shift;
      this.i++;
    }

    if ((first4 & 0x80) !== 0) {
      const fifth = this.data.getUint8(this.i);
      result |= (fifth & 0x7f) << 28;
      this.i++;
    }

    return result;
  }

  zigZagVarint(): number {
    const int = this.varint();
    return (int >>> 1) ^ (-(int & 1));
  }

  skip(n: number) {
    this.i += n;
  }

  skipString() {
    const length = this.data.getUint16(this.i);
    this.i += 2 + length;
  }

  skipArray(width: number) {
    const length = this.int();
    this.i += length * width;
  }
}