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From: Eric Jacoboni <jaco@neottia.net>
Newsgroups: comp.lang.ada
Subject: Re: TCP/IP Sockets with GNAT.Sockets
Date: Mon, 02 May 2005 07:58:06 +0200
Organization: Rogntudju & Associates
Message-ID: <020520050758066354%jaco@neottia.net>
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In article <1115001752.291144.218410@z14g2000cwz.googlegroups.com>,
fabio de francesco <fmdf@tiscali.it> wrote:

> I hadn't too many problems with exchanging messages and everything
> works. The problem is that I was only able to use Streams for
> communicating between them and I can't understand at all how to use
> Receive_Socket() and Send_Socket() because they use
> "Stream_Element_Array" and "Stream_Element _Offset" in place of
> Strings. I know that by using Streams they can't communicate with C
> programs and I've read that Streams are everything but efficient.

Streams are ok if you manage both the server and the client program.
Otherwise, for talking to a server already written, send and receive
are ok.

> (2) The following is an extract from the client program. It compiles
> and works as it is. May you please explain how to modify it in order to
> use the above-mentioned functions in place of Input() and Output()? If
> the problem can be solved by copying Strings to Stream_Element_Array
> and back, how can I do that?

Here is a simple test code that use send/receive to talk to a POP3
server :

with Gnat.Sockets;     use Gnat.Sockets;
with Ada.Text_Io;      use Ada.Text_Io;
with Ada.Exceptions;   use Ada.Exceptions;
with Ada.Streams;      use Ada.Streams;
with Ada.Command_Line; use Ada.Command_Line;

procedure GetPop3 is

   -- Constantes globales
   BUFSIZ : constant := 256;
   PORT_DEFAUT : constant Port_Type := 110;  
   Protocol_Error : exception;

   -- Wrapper pour Send_Socket
   procedure Send(Sock : in Socket_Type; S : in String) is
      subtype SEA is Stream_Element_Array(1..S'Length);
      My_SEA : SEA;
      for My_SEA'Address use S(S'First)'Address;
      Trash : Stream_Element_Offset;
   begin
      Send_Socket(Sock, My_Sea, Trash);
   end Send;
   
   -- Wrapper pour Receive_Socket
   procedure Receive(Sock : in Socket_Type; S : out String; 
                     Taille : out Natural) is
      subtype SEA is Stream_Element_Array(1..S'Length);
      My_SEA : SEA;
      for My_SEA'Address use S(S'First)'Address;
      Trash : Stream_Element_Offset;
   begin
      Receive_Socket(Sock, My_Sea, Trash);
      Taille := Natural(Trash);
   end Receive;
   
   function Get_Reponse (Sock : Socket_Type) return String is
      Tampon : String(1..BUFSIZ);
      Dernier : Natural;
   begin
      Receive(Sock, Tampon, Dernier);
      return Tampon(1..Dernier); 
   end Get_Reponse ;

   procedure Is_Ok (Reponse : in String) is
   begin
      if Reponse(1..3) /= "+OK" then
         raise Protocol_Error;
      end if;
   end Is_Ok;

   procedure Connexion (Sock : out Socket_Type;
                        Serveur, User, Pass : in String;
                        Port : in Port_Type := PORT_DEFAUT) is
      Adresse : Sock_Addr_Type;
   begin
      -- Construction de l'adresse
     Adresse.Addr := Addresses(Get_Host_By_Name (Serveur));
     Adresse.Port := PORT_DEFAUT;

     -- Creation et connexion de la socket � l'adresse
     Initialize;
     Create_Socket(Sock);           
     Connect_Socket(Sock, Adresse);

     Is_Ok(Get_Reponse(Sock));
     Send(Sock, "user " & User & ASCII.CR & ASCII.LF);
     Is_Ok(Get_Reponse(Sock));
     Send(Sock, "pass " & Pass & ASCII.CR & ASCII.LF);
     Is_Ok(Get_Reponse(Sock));
   end Connexion;

   procedure Commande (Sock : in Socket_Type;
                       Cde  : in String) is
   begin
      Send(Sock, Cde & ASCII.CR & ASCII.LF);
   end Commande;
   
   Sock : Socket_Type;

begin   -- Prog principal
   if Argument_Count /= 3 then
      Put_Line("Usage: " & Command_Name & " <serveur> <user>
<password>");
   else
      begin
         Connexion(Sock, Argument(1), Argument(2), Argument(3));
         Put_Line("Connexion ok");
         Commande(Sock, "stat");
         Put_Line(Get_Reponse(Sock));
         Close_Socket(Sock);
      exception
    when Protocol_Error =>
       Put_Line(Current_Error, "Requete incorrecte");
         when E: others =>
            Put_Line(Exception_Name(E) & ": " & Exception_Message(E));
      end;
   end if;
end GetPop3;



Hope this helps,

-- 
jaco