Re: Sockets, Streams, and Element_Arrays: Much confusion

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2022-12-31 13:11, Mark Gardner wrote:

> GNAT.Sockets gives me a Stream_Element_Array, which I can't find any 
> documentation on how to make use of other than "You should also be able 
> to get a Stream, which you should use instead" (About ten years ago, on 
> this very newsgroup, somebody said not to use streams with UDP, or at 
> least not GNAT.Sockets.Stream).

Stream_Element_Array is declared in Ada.Streams as

    type Stream_Element_Array is
       array(Stream_Element_Offset range <>) of
          aliased Stream_Element;

For communication purpose it is an array of octets. Your datagram is 
represented as a Stream_Element_Array or a slice of.

As for streams, yes, it does not make sense to use them for networking, 
unless you override all stream primitives. The reasons for that are

- non-portability of predefined primitives
- low efficiency for complex data types
- encoding inefficiency as well

You will need to handle some application protocol artifacts, checksums, 
counters, strange encodings, sequence number etc. It is easier to this 
directly on the Stream_Element_Array elements.

And, well, do not use UDP, expect for broadcasting. There is no reason 
to use it. For multicast consider delivery-safe protocols like PGM. For 
single cast use TCP/IP. (If you need low latency see the socket NO_DELAY 
option)

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de