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Newsgroups: comp.lang.ada
Date: Wed, 6 Feb 2019 15:10:35 -0800 (PST)
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Subject: Ada x <whatever> Datagram Sockets
From: "Rego, P." <pvrego@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:55448
Date: 2019-02-06T15:10:35-08:00
List-Id: <comp.lang.ada>

I am trying to communicate a Windows Ada application with another application in the same machine (an specific C++ porting called MQL) using datagram sockets. The core Ada app was extracted from GNAT.Sockets documentation, from the ping-pong caller. 

with GNAT.Sockets;
with Text_IO;
with Ada.Exceptions; use Ada.Exceptions;

procedure DG_SERVER is
   package SOCKETS renames GNAT.Sockets;
   Socket  : SOCKETS.Socket_Type;
   Address : SOCKETS.Sock_Addr_Type;
   Channel : SOCKETS.Stream_Access;
   Group : constant String := "239.255.128.128";

begin

   SOCKETS.Initialize;
   SOCKETS.Create_Socket (Socket, SOCKETS.Family_Inet, SOCKETS.Socket_Datagram);
   SOCKETS.Set_Socket_Option
     (Socket,
      SOCKETS.Socket_Level,
      (SOCKETS.Reuse_Address, True));
   SOCKETS.Set_Socket_Option
     (Socket,
      SOCKETS.IP_Protocol_For_IP_Level,
      (SOCKETS.Multicast_TTL, 1));
   SOCKETS.Set_Socket_Option
     (Socket,
      SOCKETS.IP_Protocol_For_IP_Level,
      (SOCKETS.Multicast_Loop, True));
   Address.Addr := SOCKETS.Any_Inet_Addr;
   Address.Port := 55505;
   SOCKETS.Bind_Socket (Socket, Address);
   SOCKETS.Set_Socket_Option
     (Socket,
      SOCKETS.IP_Protocol_For_IP_Level,
      (SOCKETS.Add_Membership, SOCKETS.Inet_Addr (Group), SOCKETS.Any_Inet_Addr));
   Address.Addr := SOCKETS.Inet_Addr (Group);
   loop
      Channel := SOCKETS.Stream (Socket, Address);
      declare
         Message : String := String'Input (Channel);
      begin
         Address := SOCKETS.Get_Address (Channel);
         Text_IO.Put_Line (Message & " from " & SOCKETS.Image (Address));
         String'Output (Channel, Message);
      end;
   end loop;
exception
   when The_Error : others =>
      Text_IO.Put_Line("!!! "&Ada.Exceptions.Exception_Information (The_Error));
end DG_SERVER;

The problem is that when I send the message (from MQL side), my Ada server returns

raised GNAT.SOCKETS.SOCKET_ERROR : [10040] Message too long
Call stack traceback locations:
0x424e6c 0x426ddb 0x426e17 0x4200a8 0x42174e 0x4019fc 0x40246d 0x4013db 0x74198482 0x778f3ab6 0x778f3a86

and investigating the libraries, Channel : SOCKETS.Stream_Access will really receive any data size.

So... how can avoid the exception?

Thanks!