A CBOR encoder in TypeScript

cbor-encoder.ts

class CBOREncoder {
  private entryCount: number = 0;
  private data: Uint8Array = Uint8Array.from([]);

  pushBool(key: string, value: boolean): void {
    this.entryCount++;
    this.pushTextInternal(key);
    this.pushBoolInternal(value);
  }

  pushText(key: string, value: string): void {
    this.entryCount++;
    this.pushTextInternal(key);
    this.pushTextInternal(value);
  }

  pushBytes(key: string, value: Uint8Array): void {
    this.entryCount++;
    this.pushTextInternal(key);
    this.pushBytesInternal(value);
  }

  serialise(): Uint8Array {
    const size = this.data.length + 1;
    if (size > 0xffff) throw new Error('Metadata too large.');
    if (this.entryCount > 0x1f) throw new Error('Too many map entries.');

    const ret = appendBytes(
      Uint8Array.from([0xa0 + this.entryCount]),
      this.data,
      Uint8Array.from([0, 0]),
    );
    ret[size] = size >> 8;
    ret[size + 1] = size & 0xff;
    return ret;
  }

  private appendBytes(...bufs: Uint8Array[]): void {
    this.data = appendBytes(this.data, ...bufs);
  }

  private pushBoolInternal(value: boolean): void {
    this.appendBytes(Uint8Array.from([value ? 0xf5 : 0xf4]));
  }

  private pushBytesInternal(value: Uint8Array): void {
    const len = value.length;
    if (len < 24) {
      this.appendBytes(Uint8Array.from([0x40 + len]), value);
    } else if (len <= 256) {
      this.appendBytes(Uint8Array.from([0x58, len]), value);
    } else {
      throw new Error('Byte string too large.');
    }
  }

  private pushTextInternal(value: string): void {
    const valueBuf = new TextEncoder().encode(value);
    const len = valueBuf.length;
    if (len < 24) {
      this.appendBytes(Uint8Array.from([0x60 + len]), valueBuf);
    } else if (len <= 256) {
      this.appendBytes(Uint8Array.from([0x78, len]), valueBuf);
    } else {
      throw new Error('Text string too large.');
    }
  }
}

function appendBytes(main: Uint8Array, ...bufs: Uint8Array[]): Uint8Array {
  const bufsLen = bufs.reduce((total, buf) => total + buf.length, 0);
  let skipLen = main.length;
  const ret = new Uint8Array(bufsLen + skipLen);
  ret.set(main);
  bufs.forEach(buf => {
    ret.set(buf, skipLen);
    skipLen += buf.length;
  });
  return ret;
}