code: def handshake_headers(self):
          
          headers = [
              ('Host', self.host),
              ('Connection', 'Upgrade'),
              ('Upgrade', 'WebSocket'),
              ('Sec-WebSocket-Key', self.key.decode('utf-8')),
              # Origin is proxyed from the downstream server, don't set it twice
              # ('Origin', self.url),
              ('Sec-WebSocket-Version', str(max(WS_VERSION)))
          ]
  
          if self.protocols:
              headers.append(('Sec-WebSocket-Protocol', ','.join(self.protocols)))
  
          if self.extra_headers:
              headers.extend(self.extra_headers)
  
          logger.info("Handshake headers: %s", headers)
          return headers
docs: List of headers appropriate for the upgrade
          handshake.