Optimization of websocket masking

as titled

This is a cause of poor performance.

Lines 85 to 88 in 0980f9d

    
           // mask body 
        
           for (let i = 0; i < bodyLength; ++i) { 
        
             buffer[offset + i] = frameData[i] ^ maskKey[i & 3] 
        
           }

Well. we could reduce the for loop overhead by doing 4 masking operations instead of one.

As I indicated earlier. The masking is as far as I know totally useless for backend and could just be skipped...

Maybe instead of i + 4 < length, you precalculate that too

const lengthFor4 = length - (length & 3)

import { randomBytes } from "crypto";
import { group, bench, run } from "mitata";

function maskForOne(mask, buffer) {
  const alloc = Buffer.allocUnsafe(buffer.length);
  for (let i = 0; i < buffer.length; ++i) {
    alloc[i] = buffer[i] ^ mask[i & 3];
  }
  return alloc;
}

function maskForFour(mask, buffer) {
  const length = buffer.length;
  const alloc = Buffer.allocUnsafe(buffer.length);
  const lengthFor4 = length - (length & 3);
  if (length > 3) {
    for (let i = 0; i < lengthFor4; i += 4) {
      alloc[i] = buffer[i] ^ mask[0];
      alloc[i + 1] = buffer[i + 1] ^ mask[1];
      alloc[i + 2] = buffer[i + 2] ^ mask[2];
      alloc[i + 3] = buffer[i + 3] ^ mask[3];
    }
  }
  for (let i = lengthFor4; i < length; ++i) {
    alloc[i] = buffer[i] ^ mask[i & 3];
  }
  return alloc;
}

group("mask", () => {
  const buffer = new Uint8Array(randomBytes(1024 * 4).buffer);
  const mask = new Uint8Array(randomBytes(4).buffer);
  bench("for 1", () => maskForOne(mask, buffer));
  bench("for 4", () => maskForFour(mask, buffer));
});

await run();

• mask
------------------------------------------------- -----------------------------
for 1      13'381 ns/iter     (6'200 ns … 536 µs)  7'400 ns    123 µs    188 µs
for 4       9'444 ns/iter   (5'800 ns … 4'131 µs)  7'000 ns    122 µs    197 µs

summary for mask
  for 4
   1.42x faster than for 1

maybe for the last potential 3 operations a duffs device?

yes?

Something like this. Sry, I still suffer from a heat stroke and cant provide better code.

switch (length & 3) {
  case 3:
    buffer[i + 3] ^ mask[3]
  case 2:
    buffer[i + 2] ^ mask[2]
  case 2:
    buffer[i + 1] ^ mask[1]
  ...

Take care and get well soon.

	// mask body
	for (let i = 0; i < bodyLength; ++i) {
	buffer[offset + i] = frameData[i] ^ maskKey[i & 3]
	}