UNIX IPC Datagram Reliability under - (nf)

[rpw3 at fortune.UUCP]

#R:allegra:-220500:fortune:11600053:000:1040
fortune!rpw3    Feb  7 00:45:00 1984

+--------------------
| From:  Peter Vanderbilt <pv.usc-cse at rand-relay>
| 
| It would be convenient to be able to reliably send one message
| without going through the trouble (and overhead) of setting up
| a stream.
+--------------------

That's what the Xerox NS "Packet Exchange" protocol is all about.

Even so, you should be careful to set up your services to be idempotent.
Since any given packet may be lost/duplicated, it should be o.k. for a
given request (with the same tag/cookie/handle) so be acted on more
than once. Note that UNIX read's and write's have this property, if the
file offset ["lseek" pointer] is included in the request, and you don't
do a second operation 'til the first has succeeded.  (Unfortunately,
"open" and "close" are harder, without additional state in the server
that the simple protocol was designed to avoid in the first place.)

Rob Warnock

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