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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Gnat Sockets & Streams
Date: Sat, 15 Sep 2012 18:02:34 +0100
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Date: 2012-09-15T18:02:34+01:00
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"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:

(from bitter experience communicating with many different device
types/protocols)

> Using streams and sockets you should remember:
>
> 1. Stream attributes are not portable. The only type you should read/write
> into the socket stream is Unsigned_8 or equivalent (octet).

But you are not likely to have much trouble if you use the same
compiler, and ideally the same version, on either side.

> 2. As with any I/O you should honestly implement all layers of the protocol
> at hand. Don't try shortcuts like stream type attributes, representation
> clauses etc.

The stream type attributes may well be OK, and (as above) if you have
the same compiler either end you will probably be OK. It's quite another
matter if your Ada has to talk to someone else's C.

> 3. Network protocols are packet-oriented. You have to use Write (of the
> type Root_Stream_Type) instead of attributes to ensure that the packet is
> sent as a whole. It matters for both UDP and TCP/IP.

This is SO TRUE for UDP. I've never used multicast but anywhere there
are datagrams you need to heed this!

The approach we adopted was to use a memory stream (eg [1]) and then use
Write on the resulting Stream_Element_Array.

Not sure why it would matter for TCP? (unless you've used TCP_NO_DELAY,
of course).

[1] http://booch95.svn.sourceforge.net/viewvc/booch95/trunk/src/bc-support-memory_streams.ads?revision=1420&view=markup