WebSockets server tutorial

server.js

function parseMessage (buffer) {
  const firstByte = buffer.readUInt8(0);
  const isFinalFrame = Boolean((firstByte >>> 7) & 0×1); 
  const [reserved1, reserved2, reserved3] = [ Boolean((firstByte >>> 6) & 0×1), Boolean((firstByte >>> 5) & 0×1), Boolean((firstByte >>> 4) & 0×1) ]; 
  const opCode = firstByte & 0xF; 
  // We can return null to signify that this is a connection termination frame 
  if (opCode === 0×8) 
     return null; 
  // We only care about text frames from this point onward 
  if (opCode !== 0×1) 
    return; 
  const secondByte = buffer.readUInt8(1); 
  const isMasked = Boolean((secondByte >>> 7) & 0×1); 
  // Keep track of our current position as we advance through the buffer 
  let currentOffset = 2; let payloadLength = secondByte & 0×7F; 
  if (payloadLength > 125) { 
    if (payloadLength === 126) { 
      payloadLength = buffer.readUInt16BE(currentOffset); 
      currentOffset += 2; 
    } else { 
      // 127 
      // If this has a value, the frame size is ridiculously huge! 
      const leftPart = buffer.readUInt32BE(currentOffset); 
      const rightPart = buffer.readUInt32BE(currentOffset += 4); 
      // Honestly, if the frame length requires 64 bits, you're probably doing it wrong. 
      // In Node.js you'll require the BigInt type, or a special library to handle this. 
      throw new Error('Large payloads not currently implemented'); 
    } 
  }
}