Function decodeOpcodeHistogram

packages/node/src/frameAudit.ts:90–124

(bytes: Uint8Array)

}

function decodeOpcodeHistogram(bytes: Uint8Array): Readonly<{
  histogram: Readonly<Record<string, number>>;
  valid: boolean;
}> {
  const cmdCount = readHeaderU32(bytes, 24);
  const cmdOffset = readHeaderU32(bytes, 16);
  const cmdBytes = readHeaderU32(bytes, 20);
  if (cmdCount === null || cmdOffset === null || cmdBytes === null) {
    return Object.freeze({ histogram: Object.freeze({}), valid: false });
  }
  if (cmdCount === 0) {
    return Object.freeze({ histogram: Object.freeze({}), valid: true });
  }
  if (cmdOffset < 0 || cmdBytes < 0 || cmdOffset + cmdBytes > bytes.byteLength) {
    return Object.freeze({ histogram: Object.freeze({}), valid: false });
  }
  const dv = new DataView(bytes.buffer, bytes.byteOffset, bytes.byteLength);
  let off = cmdOffset;
  const end = cmdOffset + cmdBytes;
  const hist: Record<string, number> = Object.create(null) as Record<string, number>;
  for (let i = 0; i < cmdCount; i++) {
    if (off + 8 > end) {
      return Object.freeze({ histogram: Object.freeze(hist), valid: false });
    }
    const opcode = dv.getUint16(off + 0, true);
    const size = dv.getUint32(off + 4, true);
    if (size < 8 || off + size > end) {
      return Object.freeze({ histogram: Object.freeze(hist), valid: false });
    }
    const key = String(opcode);
    hist[key] = (hist[key] ?? 0) + 1;
    off += size;
  }
  return Object.freeze({ histogram: Object.freeze(hist), valid: off === end });
}

function nowUs(): number {
  return Math.round(performance.now() * 1000);