Hi Martin,
True, but the difference is that HTTP servers typically can use some
sort of time-out mechanism to close idling persistent connections and
free resources. Callout servers can't do that because such a behavior
could result in the loss of application message data and the OPES
processor may not necessarily be able to repeat a callout
request (since
it cannot always keep a copy of application messages).
Think of a very simple callout protocol that starts each request with a
little handshake before application data is transfered (like in SMTP).
For such a protocol it will be possible to timeout a connection by the
callout server without loosing data if the next request is just about to
be sent in this moment.
I agree, but this approach would kind of defeat the purpose of why we
want to use persistent connections in the first place, i.e. to avoid
handshakes and the like before each and every callout transaction.
Yes, this would be feasible (but not necessarily very efficient).
Absolutely. And that's why an OPES protocol SHOULD offer a keep-alive
mechanism.
How about we leave the requirement for a keep-alive mechanism in the
document, but add a sentence that says that the callout protocol MAY
choose to use an implicit mechanism in order to check the health status
of a callout connection endpoint, e.g. the parameter negotiation process.
-Andre