Chapter 3

Protocol Specification

The current protocol specification is available in XML format here and the corresponding XML DTD here.

In that protocol specification:

  • a request or event with the XML attribute type="destructor" marks the message as destructor.
  • an argument with an XML attribute enum carries a value of the corresponding enum
  • an argument with an XML attribute interface attribute indicates that an object in the same message is of that interface type
  • an argument with an XML attribute interface_arg attribute indicates that an object in the same message is of the interface given in the named argument.
  • an enum with an XML attribute bitfield indicates a single-bit value.
  • each request, event or enum has an XML attribute since to indicate the interface version this request, event or enum was introduced in
  • each interface has an XML attribute version indicate the current version of this interface

Protocol violations

The term “Protocol Violation” is used to indicate that the client or the EIS implementation have sent a message that is not allowed by the protocol specification. A protocol violation must result in immediate disconnection. In the case of the EIS implementation it is permitted to send the ei_connection.disconnect event to the client to notify them of the protocol violation.


A request or event marked as destructor causes the object to be destroyed by the sender immediately after sending the request or event. On the receiving side the object must thus be treated as defunct and no further interaction with the object is permitted.

Note that due to the asynchronous nature of the protocol, some messages may have been sent before the destructor message was received. Both client and EIS implementation must handle this case gracefully. In the EIS implementation for example, it is usually enough to reply with the ei_connection.invalid_object event.