Re: Ada x <whatever> Datagram Sockets

[Simon Wright <simon@pushface.org>]

"Randy Brukardt" <randy@rrsoftware.com> writes:

> "Simon Wright" <simon@pushface.org> wrote in message 
> news:ly5ztry1f8.fsf@pushface.org...
>> "Randy Brukardt" <randy@rrsoftware.com> writes:
> ...
>> [1] not sure that FIFO_Streams offers this without copying the contents
>> out?
>
> It doesn't, but I'm not sure how it could. It's not possible for a single 
> data type to be two different streams at the same time. Moreover, at least 
> some of the time, the result isn't going to a stream at all. And I haven't 
> personally seen a case where the extra cost of copying the data is 
> significant (the target stream/API being much slower). I could see where it 
> might matter, particularly in a transfer to some other kind of memory.

You may well be right about the extra cost. As I saw it, I needed to
eliminate the need for the users to declare a buffer, read into it, and
send it to the socket (represented in GNAT.Sockets as a stream), when
there was already a perfectly good buffer in the memory stream. There
were quite a few users.

I had fun getting FIFO_Streams to build in Ada 2012. Obviously had to
remove the 2020 aspects, and recast the (declare ...). Only the bounded
version, because the unbounded version would be much more
work. Unfortunately this means GNATprove couldn't be used, because
SPARK2014 doesn't allow discriminants on derived types (SPARK RM
3.7(2)). All the same, the assertions were a huge help.

Test code:

   with Ada.Streams.FIFO_Streams.Bounded;
   with Ada.Text_IO; use Ada.Text_IO;
   procedure Test is
      S : aliased Ada.Streams.FIFO_Streams.Bounded.Stream_Type (31);
   begin
      for J in 1 .. 9 loop
         String'Output (S'Access, "hello!" & J'Image);
         declare
            Buff : Ada.Streams.Stream_Element_Array (1 .. 32);
            Last : Ada.Streams.Stream_Element_Offset;
         begin
            S.Read (Item   => Buff,
                    Last   => Last);
            for K in 1 .. Last loop
               Put (Buff (K)'Image);
            end loop;
            New_Line;
         end;
      end loop;
   end Test;

Output:

   $ ./test
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 49
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 50
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 51
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 52
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 53
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 54
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 55
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 56
    1 0 0 0 8 0 0 0 104 101 108 108 111 33 32 57