Need a sample/demo of using TIdTelnet to interact with telnet server - delphi

Question

I tried to employ Indy 10.5.5 (shipped with Delphi 2010) for:
connecting to telnet server
performing username/password authentication (gaining access to the command shell)
executing a command with returning resulting data back to application
and had no success, additionally i'm completely lost in spaghetti logic of Indy's internals and now have no idea why it didnt work or how i supposed to send strings to the server and grab the results. Need some sample code to study.
Formal form of the question: Where can i get 3-rd party contributed demo covering TIdTelnet component? (indyproject.org demos webpage do not have one)

Answer 1

The main problem with Telnet is that it DOES NOT utilize a command/response model like most other Internet protocols do. Either party can send data at any time, and each direction of data is independant from the other direction. This is reflected in TIdTelnet by the fact that it runs an internal reading thread to receive data. Because of this, you cannot simply connect, send a command, and wait for a response in a single block of code like you can with other Indy components. You have to write the command, then wait for the OnDataAvailable event to fire, and then parse the data to determine what it actually is (and be prepared to handle situations where partial data may be received, since that is just how TCP/IP works).
If you are connecting to a server that actually implements a command/response model, then you are better off using TIdTCPClient directly instead of TIdTelnet (and then implement any Telnet sequence decoding manually if the server really is using Telnet, which is rare nowadays but not impossible). For Indy 11, we might refactor TIdTelnet's logic to support a non-threaded version, but that is undecided yet.

Answer 2

done with indy.
no comments.. just som old code :-)
telnet don't like the send string kommand.. use sendch.
telnetdude.Host := 1.1.1.1;
try
telnetdude.connect;
except
on E: Exception do begin
E.CleanupInstance;
end; {except}
if telnetdude.Connected then begin
for i := 1 to length(StringToSend) do telnetdude.sendch(StringToSend[i]);
telnetdude.sendch(#13);
end;
end; {while}
end; {if}
if telnetdude.Connected then telnetdude.Disconnect;
end;

Answer 3

I hope this helps anyone looking for answers to a similar question.
Firstly, It would seem the typical command/response model (as mentioned above, does indeed NOT apply).
So I just got it working for some very simple application (rebooting my router).
Specific additions to above code from Johnny Lanewood (and perhaps some clarification)
a) You have to send #13 to confirm the command
b) I got "hangs" on every command I sent / response I requested UNTIL I enabled ThreadedEvent. (this was my big issue)
c) the OnDataAvailable event tells you when new data is available from the Telnet Server - however there are no guarantees as to what this data is - i.e. it's pretty what you get in the command line / what ever is appended to the previous responses. But is is NOT a specific response line to your command - it's whatever the telnet server returns (could be welcome info, ASCII drawings etc etc.)
Given (c) above, one would rather check the OnDataAvailable event and parse the data (knowing what you'd expect). When the output stops (i.e. you need build a mechanism for this), you can parse the data and determine whether the server is ready for something new from the client. For the purpose of my code below, I set a read timemout and I just used Sleep(2000) - ignorantly expecting no errors and that the server would be ready after the sleep for the next command.
My biggest stumbling block was ThreadedEvent := True (see above in b)
Thus, my working solution (for specific application, and possibly horrible to some).
lIDTelnet := TIdTelnet.Create(nil);
try
lIdTelnet.ReadTimeout := 30000;
lIDTelnet.OnDataAvailable := TDummy.Response;
lIDTelnet.OnStatus := TDummy.Status;
lIdTelnet.ThreadedEvent := True;
try
lIDTelnet.Connect('192.168.0.1', 23);
if not lIDTelnet.Connected then
Raise Exception.Create('192.168.0.1 TELNET Connection Failed');
Sleep(2000);
lIdtelnet.SendString(cst_user + #13);
Sleep(2000);
lIdtelnet.SendString(cst_pass + #13);
Sleep(2000);
lIdtelnet.SendString(cst_reboot + #13);
Sleep(2000);
if lIDTelnet.Connected then
lIDTelnet.Disconnect;
except
//Do some handling
end;
finally
FreeAndNil(lIdTelnet);
end;
and then
class procedure TDummy.Response(Sender: TIdTelnet; const Buffer: TIdBytes);
begin
Write(TDummy.ByteToString(Buffer));
end;
class function TDummy.ByteToString(
const aBytes: TIdBytes): String;
var
i : integer;
begin
result := '';
for i := 0 to Length(aBytes) -1 do
begin
result := result + Char(aBytes[i]);
end;
end;