Pascal (Lazarus/Delphi)

Release an SSH Channel's Local Resources

Demonstrates the Chilkat Ssh.ChannelRelease method, which releases Chilkat's retained local resources for a channel after all output and exit information has been retrieved. The only argument is the channel number.

Background: Chilkat retains a channel's buffered output and exit information after the channel closes, so you can still read a command's final output. That retention costs memory, and a long-running program that opens many channels should release each one when finished with it. Note this is not a channel-closing method — it sends neither EOF nor CLOSE. Retrieve everything you need first, because releasing discards it.

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Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.Ssh;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  ssh: TSsh;
  sshPort: Integer;
  password: string;
  channelNum: Integer;
  output: string;

begin
  success := False;

  //  Demonstrates the Ssh.ChannelRelease method, which releases Chilkat's retained local resources
  //  for a channel after all output and exit information has been retrieved.  The only argument is
  //  the channel number.

  ssh := TSsh.Create;

  sshPort := 22;
  success := ssh.Connect('ssh.example.com',sshPort);
  if (success = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  //  Normally you would not hard-code the password in source.  You should instead obtain it
  //  from an interactive prompt, environment variable, or a secrets vault.
  password := 'mySshPassword';

  success := ssh.AuthenticatePw('mySshLogin',password);
  if (success = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  //  Open a session channel.  A negative return value indicates failure.
  channelNum := ssh.OpenSessionChannel();
  if (channelNum < 0) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  success := ssh.SendReqExec(channelNum,'uname -a');
  if (success = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  //  IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
  //  it, this call waits forever if the server never sends channel close.
  ssh.ReadTimeoutMs := 15000;

  //  Retrieve everything of interest before releasing the channel.
  success := ssh.ChannelReceiveToClose(channelNum);
  if (success = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  output := ssh.GetReceivedText(channelNum,'utf-8');
  if (ssh.LastMethodSuccess = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;
  WriteLn(output);

  //  Release the retained local resources.  This does not send EOF or CLOSE.
  ssh.ChannelRelease(channelNum);

  ssh.Disconnect();


  ssh.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.