How can two applications communicate with each other if they are running on different machines?

unit Chris;

interface


uses  SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls, ExtCtrls, Menus, IniFiles, Buttons, ComCtrls,
  Spin, Registry, FileCtrl, ShellAPI, WinSvc;

// -----------------------------------------------------------------------
// First of all the Type-Definitions

Type
  TChMailSlot = class
    LastError: String;
    function CreateLocalServer(MailSlotName: String): Boolean;
    function CreateRemoteServer(Server, MailSlotName: String): Boolean;
    function CreateLocalClient(MailSlotName: String): Boolean;
    function CreateRemoteClient(Server, MailSlotName: String): Boolean;
    function ReadMail : String;
    function WriteMail(Text: String) : Boolean;
    procedure CloseServer;
    procedure CloseClient;
  private
    { Private declarations }
    FMailslotServer : THandle;
    FMailslotClient : THandle;
  public
    { Public declarations }
  end;

Var ChMailSlot : TChMailSlot;


implementation


{ -----------------------------------------------------------------------------}
{ --------------------   Begin of TChMailSlot-Declarations   ----------------- }
{ -----------------------------------------------------------------------------}

function TChMailSlot.CreateLocalServer(MailSlotName: String): Boolean;
const cERRNOCREATE   = 'The Mailslot %s could not be created';
      cSUCCESSCREATE = 'The Mailslotserver %s has been created';
begin
  LastError:= '';
  FMailslotServer := CreateMailslot(PChar('\\.\mailslot\'+MailSlotName), 0, 0, nil);
  if FMailslotServer = Invalid_Handle_Value then begin
    Result:= False;
    LastError:= Format(cERRNOCREATE, [MailSlotName]);
  end else begin
    Result:= True;
    LastError:= Format(cSUCCESSCREATE, [MailSlotName]);
  end;
end;

function TChMailSlot.CreateRemoteServer(Server, MailSlotName: String): Boolean;
const cERRNOCREATE   = 'The Mailslot %s could not be created';
      cSUCCESSCREATE = 'The Mailslotserver %s has been created';
begin
  LastError:= '';
  FMailslotServer := CreateMailslot(PChar('\\'+Server+'\mailslot\'+MailSlotName), 0, 0, nil);
  if FMailslotServer = Invalid_Handle_Value then begin
    Result:= False;
    LastError:= Format(cERRNOCREATE, [MailSlotName]);
  end else begin
    Result:= True;
    LastError:= Format(cSUCCESSCREATE, [MailSlotName]);
  end;
end;

function TChMailSlot.CreateLocalClient(MailSlotName: String): Boolean;
Const cERRNOOPEN     = 'The Mailslot %s could not be opened.';
      cSUCCESSCREATE = 'The Mailslotclient %s could be created';
begin
  FMailslotClient := CreateFile(PChar('\\.\mailslot\'+MailSlotName), Generic_Write, File_Share_Read,
                          nil, Open_Existing, File_Attribute_Normal, 0);
  if FMailslotClient = INVALID_HANDLE_VALUE then begin
    Result:= False;
    LastError:= Format(cERRNOOPEN, [MailSlotName]);
  end else begin
    Result:= True;
    LastError:= Format(cSUCCESSCREATE, [MailSlotName]);
  end;
end;

function TChMailSlot.CreateRemoteClient(Server, MailSlotName: String): Boolean;
Const cERRNOOPEN     = 'The Mailslot %s could not be opened.';
      cSUCCESSCREATE = 'The Mailslotclient %s was be created successfully';
begin
  FMailslotClient := CreateFile(PChar('\\'+Server+'\mailslot\'+MailSlotName), Generic_Write, File_Share_Read,
                          nil, Open_Existing, File_Attribute_Normal, 0);
  if FMailslotClient = INVALID_HANDLE_VALUE then begin
    Result:= False;
    LastError:= Format(cERRNOOPEN, [MailSlotName]);
  end else begin
    Result:= True;
    LastError:= Format(cSUCCESSCREATE, [MailSlotName]);
  end;
end;

function TChMailSlot.ReadMail : String;
const cERRNOINFO     = 'Reading Mailslot information not possible.';
      cERRNOREAD     = 'It was not possible to read the information from the Mailslot.';
Var  iMsgSize : DWord;
     iRead    : DWord;
     sMsg     : String;
begin
  Result:= '';
  LastError:= '';
  if not GetMailslotInfo(FMailslotServer, nil, iMsgSize, nil, nil) then
  begin
    LastError:= cERRNOINFO;
  end;
  if iMsgSize <> MAILSLOT_NO_MESSAGE then
    begin
      SetLength(sMsg, iMsgSize);
      if not ReadFile(FMailslotServer, sMsg[1], iMsgSize, iRead, nil) then
        begin
          LastError:=cERRNOREAD;
        end;
      Result:= sMsg;
    end;
end;

function TChMailSlot.WriteMail(Text: String) : Boolean;
const cERRNOWRITE = 'It was not possible to send the information to the Mailslot.';
var
  iBytes : DWord;
  sMsg   : String;
begin
  sMsg := Text;
  LastError:= cERRNOWRITE;
  Try
    WriteFile(FMailslotClient, sMsg[1], Length(sMsg), iBytes, nil);
    Result:= True;
    LastError:='';
  except
    LastError:= cERRNOWRITE;
    Result:= False;
  end;
end;


procedure TChMailSlot.CloseServer;
begin
  CloseHandle(FMailslotServer);
end;

procedure TChMailSlot.CloseClient;
begin
  CloseHandle(FMailslotClient);
end;

begin  { ----------------  Initialisation of the Unit ---------------- }

ChMailSlot:= TChMailSlot.Create;
END.


{ -----------------------------------------------------------------------------}
{ ---------------------- End of TChMailSlot-Declarations --------------------- }
{ -----------------------------------------------------------------------------}





{ And now a simple client-programm using the Mailslot definitions above defined in the unit Chris }

unit MainClient;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls,Chris;

type
  TForm1 = class(TForm)
    Label1: TLabel;
    Label2: TLabel;
    Messages: TEdit;
    Text: TEdit;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  ChMailSlot.CreateLocalClient('TestMailSlot');
  Messages.Text:= ChMailSlot.LastError;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  ChMailSlot.CloseClient;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  If not ChMailSlot.WriteMail(Text.Text) then begin
    MessageBeep(0);
  end;
  Messages.Text:= ChMailSlot.LastError;
  Text.SelectAll;
end;

end.




{ And the corresponding server-programm using the Mailslot definitions above defined in the unit Chris }


unit Main;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls,Chris, ExtCtrls;

type
  TForm1 = class(TForm)
    Messages: TEdit;
    Label1: TLabel;
    Text: TEdit;
    Label2: TLabel;
    Button1: TButton;
    Timer1: TTimer;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Timer1Timer(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);
begin
  ChMailSlot.CreateLocalServer('TestMailSlot');
  Messages.Text:= ChMailSlot.LastError;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  ChMailSlot.CloseServer;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Text.Text:=ChMailSlot.ReadMail;
  Messages.Text:= ChMailSlot.LastError;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
Var Mail: String;
begin
  Mail:= ChMailSlot.ReadMail;
  If Mail <> '' then begin
    Text.Text:= Mail;
    Messages.Text:= ChMailSlot.LastError;
  end;
end;

end.