The Implementation of an FTP Server

This event authenticates a user that is trying to use the FTP server. It is advisable to use a database to authenticate a particular user. In the code below, I used "myusername" and "mypassword" as the username and password:

procedure TForm1.IdFTPServer1UserLogin(ASender:TIdFTPServerContext;
const AUsername, APassword: String; var AAuthenticated:Boolean);
begin
if (AUsername = edit1.Text) and (APassword = edit2.Text) then
begin
AAuthenticated:=True
end
else
begin
AAuthenticated := False;
end;
end;

procedure TForm1.IdFTPServer1StoreFile(ASender:TIdFTPServerContext;
const AFileName: String; AAppend: Boolean; var VStream:TStream);
begin
if not Aappend then
VStream := TFileStream.Create(AFileName,fmCreate)
else
      VStream := TFileStream.Create(AFileName,fmOpenWrite)
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
idftpserver1.DefaultPort:=strtoint(edit3.text);
idftpserver1.Active:=true;
showmessage('Connected');
end;

procedure TForm1.IdFTPServer1AfterUserLogin(ASender:TIdFTPServerContext);
begin
//set home dir here
homedir:='c:';
end; 

This event is optional. It enables you to show a message when a exception occurs:

procedure TForm1.IdFTPServer1Exception(AContext: TIdContext;
AException: Exception);
begin
showmessage(AException.Message);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
idftpserver1.Active:=false;
close;
end; 

The server status event simply displays the status of the server when  there is a status change:

procedure TForm1.IdFTPServer1Status(ASender: TObject;
const AStatus: TIdStatus; const AStatusText: String);
begin
memo1.lines.add(Astatustext);
end;

procedure TForm1.IdFTPServer1Stat(ASender:TIdFTPServerContext;
AStatusInfo: TStrings);
var
i:integer;
begin
for i:= 0 to astatusinfo.Count-1 do
begin
memo1.Lines.Add(astatusinfo.Strings[i]);
end;
end;

This event gets fired when the server writes data to a client. I've included it mainly for debugging purposes. It will record all communications between the server and a client:

procedure TForm1.IdFTPServer1Execute(AContext: TIdContext);
begin
logfile1.DoLogWriteString(AContext.Connection.IOHandler.AllData);
end;

That is all there is to implementing a working FTP server. As you will no doubt notice, I have not implemented all of the commands, but the ones I implemented cover all that is required for an FTP server to function well.

Conclusion

The best way to test this application is with a graphical FTP client such as Dreamweaver instead of telnet. For some reason  the server application refuses to execute the LIST command when telnet is used. And as I've stated many times before, you cannot do anything with an FTP server that cannot show you the files in a given directory. I've notified the Indy developers about this problem, and hopefully they will work on it.