Technical Q&A NW22

Error -3168 (kOTStateChangeErr) and Handoff Endpoints

Q: I've implemented a server endpoint which hands the connection off to a handoff endpoint. After the server processes a connect request using the OTAccept call, the asynchronous handler for the handoff endpoint is passed a T_DATA event. When the handler makes the OTRcv call, however, it returns error -3168, (kOTStateChangeErr). Can you explain this?

A: This problem only occurs when there is a handoff (secondary) endpoint involved. The implementation of Open Transport makes it possible for an asynchronous handoff endpoint to receive a T_DATA event before the connect mechanism is completed. After accepting a connection, an asynchronous listener endpoint can expect to receive a T_ACCEPTCOMPLETE call. The "accepting" or handoff endpoint can expect to receive the T_PASSCON event.

It is possible for the handoff endpoint to receive the T_DATA event before receiving the T_PASSCON event. If this happens, set a flag to defer receiving the data until later. When the T_PASSCON event is received, check the flag and issue the OTRcv call if the flag is set. (Note that after deferring the handling of the T_DATA event, your handler will not be notified with this event, until you process (read) all of the data presently available.)