Package: ASCL.SV.Server

Last update: 26 Sep 99 / 08:04

Overview

This package implments a server which recevies commands from a socket connection. Upon opening a connection a a so called agent task will be started. The agent task operates on the abstract Agent datatype. The procedure create binds the agent type and the server type together.

Synopsis

type Object( Port : Positive ) is abstract tagged private;
type Reference is access all Object'
Class; 	        	
procedure Initialize( O : in Reference; Port:
in Integer := 0 );
procedure Finalize( O : in Reference );

function  Create( O : in Object ) 
return Agent.Reference is abstract;
procedure Delete( A : Agent.Object'Class ) is abstract;   

Description

Type - Object

This is the server object. As descriminant the port number is specified where the input is received from.

Type - Reference

This type is used to reference all derived instances of the ASCL.SV.Server Class.

Method - Initialize

Preconditions:

The instance is not already initialized.

Postconditions:

The instance is initialized. The main dispatching task is running an listening on the specified port.

Function:

This procedure initialitzes an instance of the server.

Exceptions:

Allready_Initialized

Method - Create

Preconditions:

The server instance is initialized.

Postconditions:

Function:

This function has to be defined within the agent defintion. If returns a new agent for the server specitfied by the Object Type.

Exceptions:

Method

Preconditions:

Postconditions:

Function:

Exceptions:

Method

Preconditions:

Postconditions:

Function:

Exceptions:

Discussion

The port number is given as part of the Object type. An attempt should be made to make this less system dependant. TCP/IP is so commonly used, that the understanding of port number will be the same in most of the sytem environements.

The server package depends on the socket package from....This should be incorperated into the ASCL.

Example

The following example shows how to implement a server which simply replies to every input: First of all a new data type Object is defined which represents the data needed per session and a Data Type Factory is defined which contains the additionaly needed server data is defined. The package specification contains additionaly the extentsions required by the abstract types of the Server and the Agent class.

*** Reply.ads ***
with ASCL.SV.Agent;
with ASCL.SV.Server;
use ASCL.SV;

with Ada.Streams; use Ada.Streams;

package Reply is
   type Object is new Agent.Object with null record;

   type Factory is new Server.Object with null record;

   procedure Initialize( O : in out Object );
   procedure Finalize( O : in out Object );
   function Process( O : in Object; Data : in Stream_Element_Array  ) 
                  return Stream_Element_Array;
   function Create( O : in Factory ) return Agent.Reference;
end Reply;

The implementation of the package is shown below. The function create returns on every call a new instance of the Agent type and the function process implements the data processing part of the agent.

*** Reply.adb ***
with Ada.Text_IO;   use Ada.Text_IO;
package body Reply is
   procedure Initialize( O : in out Object ) is 
   begin
      Put_Line( "Agent Initialize");
   end Initialize;
   procedure Finalize( O : in out Object ) is 
   begin
     Put_Line("Finalize");
   end Finalize;
   function Create( O : in Factory ) return Agent.Reference is 
      Result : Agent.Reference := new Object;
   begin
      return  Result;
   end Create;
   function Process( O : in Object; Data : in Stream_Element_Array ) 
                                return Stream_Element_Array is
   begin
      return Data;
   end Process;
end Reply;
with Reply;
with Server; use Server; 

*** Test.adb ***
procedure Test is
  P   : Server.Reference := new Reply.Factory( 3000 );
begin
  Initialize( P );
  loop
     delay 20.0;
  end loop;
  Finalize( P );
end Test;

References