code: function lookupEndPoint (local) {
    // No interfaces bound by the desired port. Note that this would also work for
    // zero, which indicates an ephemeral binding, but we check for that case
    // explicitly before calling this function.
    if (!endPoints[local.port]) return null;
  
    // Read datagram socket from cache.
    var endPoint = endPoints[local.port][local.address];
  
    // If no datagram exists, ensure that we'll be able to create one. This only
    // inspects ports that have been bound by UDT, not by other protocols, so
    // there is still an opportunity for error when the UDP bind is invoked.
    if (!endPoint) {
      if (endPoints[local.port][0]) {
        throw new Error('Already bound to all interfaces.');
      }
      if (local.address == 0) {
        throw new Error('Cannot bind to all interfaces because some interfaces are already bound.');
      }
    }
  
    // Return cached datagram socket or nothing.
    return endPoint;
  }
docs: Look up an UDP datagram socket in the cache of bound UDP datagram sockets by the user specified port and address.