WebSockets server tutorial

server.js

// Allocate somewhere to store the final message data
const data = Buffer.alloc(payloadLength);
// Only unmask the data if the masking bit was set to 1
if (isMasked) {
  // Loop through the source buffer one byte at a time, keeping track of which
  // byte in the masking key to use in the next XOR calculation
  for (let i = 0, j = 0; i < payloadLength; ++i, j = i % 4) {
  // Extract the correct byte mask from the masking key
    const shift = j == 3 ? 0 : (3 - j) << 3; 
    const mask = (shift == 0 ? maskingKey : (maskingKey >>> shift)) & 0xFF;
    // Read a byte from the source buffer 
    const source = buffer.readUInt8(currentOffset++); 
    // XOR the source byte and write the result to the data 
    buffer.data.writeUInt8(mask ^ source, i); 
  }
 } else {
  // Not masked - we can just read the data as-is
  buffer.copy(data, 0, currentOffset++);
}

typo fixes:

line 10:

const mask = (shift = 0 ? maskingKey : (maskingKey >>> shift)) & 0xFF;
should be:
const mask = (shift == 0 ? maskingKey : (maskingKey >>> shift)) & 0xFF;

line 14:

buffer data.writeUInt8(mask ^ source, i);
should be:
buffer.data.writeUInt8(mask ^ source, i);

typo fixes:

line 10:

const mask = (shift = 0 ? maskingKey : (maskingKey >>> shift)) & 0xFF;
should be:
const mask = (shift == 0 ? maskingKey : (maskingKey >>> shift)) & 0xFF;

line 14:

buffer data.writeUInt8(mask ^ source, i);
should be:
buffer.data.writeUInt8(mask ^ source, i);

Fixed, thanks!

line 9:
const shift = j = 3 ? 0 : (3 - j) << 3;
should be:
const shift = j == 3 ? 0 : (3 - j) << 3;

line 14:
buffer.data.writeUInt8(mask ^ source, i);
should be:
data.writeUInt8(mask ^ source, i);