Read an SSH Channel with a Byte Threshold

See more SSH Examples

Demonstrates the Chilkat Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also returns once newly processed data brings the total buffered data to or above a byte threshold. The arguments are the channel number, the poll timeout, and the threshold.

The integer return value is -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or channel close was processed, or — when greater than 0 — the total bytes currently buffered for the channel (not the bytes newly received by this call).

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;
  pollTimeoutMs: Integer;
  maxNumBytes: Integer;
  result: Integer;
  output: string;

begin
  success := False;

  //  Demonstrates the Ssh.ChannelReadAndPoll2 method, which works like ChannelReadAndPoll but also
  //  returns once the total buffered data reaches or exceeds a byte threshold.  The 1st argument is
  //  the channel number, the 2nd is the poll timeout, and the 3rd is the byte threshold.

  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;

  channelNum := ssh.OpenSessionChannel();
  if (channelNum < 0) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  //  Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
  //  raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
  //  echo typed commands back, and skips interactive login scripts.  The output is therefore
  //  clean and easily parseable -- but because no prompt is ever sent, code must not wait for
  //  one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
  success := ssh.SendReqShell(channelNum);
  if (success = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  success := ssh.ChannelSendString(channelNum,'cat /var/log/syslog' + #10,'utf-8');
  if (success = False) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  //  Return when output goes quiet for 500ms, or once about 64KB has been buffered.  The
  //  threshold is not a hard buffer limit -- a whole SSH packet may push the total above it.
  pollTimeoutMs := 500;
  maxNumBytes := 65536;
  //  The return value is: -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or
  //  channel close was processed, or the total number of buffered bytes when greater than 0.
  result := ssh.ChannelReadAndPoll2(channelNum,pollTimeoutMs,maxNumBytes);
  if (result = -1) then
    begin
      WriteLn(ssh.LastErrorText);
      Exit;
    end;

  if (result = -2) then
    begin
      WriteLn('No channel data arrived before the timeout.');
    end;

  if (result = 0) then
    begin
      WriteLn('EOF or channel close was processed.  Buffered data may still remain.');
    end;

  if (result > 0) then
    begin
      WriteLn('Total bytes buffered: ' + result);
    end;

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

  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.