>> STREAMS and he XTI interface did have a concept of this -- you could
>> get called back when the TCP SYN arrive.  You had the option of
>> "accepting" the connection (which would reply with another TCP SYN)
>> or rejecting it (sending a TCP RST).
>
> Not on any of the STREAMs based TCP implementations I've seen.
> IIRC the XTI for TCP explicitely states that the SYN-ACK will be
> sent before any handshake with the application takes place.
> (The same isn't true for typical implemetations of other protocols
> using the XTI/TLI and STREAMS).

I think this is how it work.

Using the STREAMS API, you:

- use t_open to create a socket in non-blocking mode

- use t_bind and t_listen to start waiting for incoming connections

- use t_look to wait for a T_CONNECT event

At this point, you have the option of accepting the connection (using  
t_accept) or disconnecting (using t_snddis).  t_accept will send a  
TCP_SYN and completion the open, while t_snddis will send a TCP_RST  
(since the connection is not yet open).

The Mac OS STREAMS implementation (based on Mentat's code) made the  
t_look stuff a little easier by allowing you to specify a callback  
when the event came in, so it was a little easier to handle.

Rob