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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada x <whatever> Datagram Sockets
Date: Fri, 8 Feb 2019 22:38:47 +0100
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Xref: reader01.eternal-september.org comp.lang.ada:55473
Date: 2019-02-08T22:38:47+01:00
List-Id: <comp.lang.ada>

On 2019-02-08 21:35, Rego, P. wrote:
>> What the OP needs to do is
>>
>> 1. Get Length, the length of the data.
>> 2. Create C : Interfaces.C.char_array (1 .. Length)
>> 3. Transfer the data into C
>> 4. Use Interfaces.C.To_Ada (C) to transform C into an Ada String
> 
> Simple enough, would you know how transfer the data into this C? I am trying in this path
> 
>     loop
>        --  Receive and print message from client Ping
>        Channel := SOCKETS.Stream (Socket, Address);
> 
>        Text_IO.Put_Line (Integer'Image (Channel'Size));
>        
>        declare
>           Channel_Size : Integer := Integer (Channel'Size);
>           type Buffer_Type is new Interfaces.C.char_array (1 .. Interfaces.C.size_t (Channel_Size));
>           type Stream_Buffer_Type is new String (1 .. Integer (Channel_Size));
> 
>           function Copy_Arr is new Ada.Unchecked_Conversion (Buffer_Type, Stream_Buffer_Type);
>           
>           --Buffer : Buffer_Type;
>           Stream_Buffer : Stream_Buffer_Type;
>           
>        begin
>           --Buffer := String'Input (Channel);
>           
>           --!!!! Stream_Buffer := Stream_Buffer_Type (String'Input (Channel));
>        end;
> end loop;

    declare
       Packet : Stream_Element_Array (1..Max_Size);
       Last   : Stream_Element_Offset;
       From   : Sock_Addr_Type;
    loop
       Receive_Socket (Socket, Packet, Last, From); -- UDP from anyone
       declare
          Text : String (1..Natural (Last));
       begin
          for Index in 1..Last loop
             Text (Integer (Index)) := Character'Val (Packet (Index));
          end loop;
          Put_Line (Image (From) & ">|" & Text & "|");
       end;
    end loop;

For UDP there is no need to have packet length because packet=frame.

For TCP, you read the header first which usually determine the length. 
Then you read the length stream elements. After that you start to decode.

P.S. It is good practice to keep framing (packet I/O) separate from 
payload encoding/decoding.

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