Poll an SSH Channel for Incoming Data

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Demonstrates the Chilkat Ssh.ChannelPoll method, which polls a channel for incoming messages, waiting at most the given number of milliseconds. The first argument is the channel number and the second is the poll timeout; pass 0 for a nonblocking poll.

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).

var
success: Integer;
ssh: TChilkatSsh;
sshPort: Integer;
password: WideString;
channelNum: Integer;
pollTimeoutMs: Integer;
result: Integer;
output: WideString;

begin
success := 0;

//  Demonstrates the Ssh.ChannelPoll method, which polls a channel for incoming messages, waiting
//  at most the given number of milliseconds.  The 1st argument is the channel number and the 2nd
//  is the poll timeout.  Pass 0 for a nonblocking poll.

ssh := TChilkatSsh.Create(Self);

sshPort := 22;
success := ssh.Connect('ssh.example.com',sshPort);
if (success = 0) then
  begin
    Memo1.Lines.Add(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 = 0) then
  begin
    Memo1.Lines.Add(ssh.LastErrorText);
    Exit;
  end;

channelNum := ssh.OpenSessionChannel();
if (channelNum < 0) then
  begin
    Memo1.Lines.Add(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 = 0) then
  begin
    Memo1.Lines.Add(ssh.LastErrorText);
    Exit;
  end;

success := ssh.ChannelSendString(channelNum,'date' + #10,'utf-8');
if (success = 0) then
  begin
    Memo1.Lines.Add(ssh.LastErrorText);
    Exit;
  end;

//  Wait up to 3 seconds for channel data.
pollTimeoutMs := 3000;
//  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.ChannelPoll(channelNum,pollTimeoutMs);
if (result = -1) then
  begin
    Memo1.Lines.Add(ssh.LastErrorText);
    Exit;
  end;

if (result = -2) then
  begin
    Memo1.Lines.Add('No channel data arrived before the timeout.');
  end;

if (result = 0) then
  begin
    Memo1.Lines.Add('EOF or channel close was processed.  Buffered data may still remain.');
  end;

if (result > 0) then
  begin
    Memo1.Lines.Add('Total bytes buffered: ' + IntToStr(result));
  end;

output := ssh.GetReceivedText(channelNum,'utf-8');
if (ssh.LastMethodSuccess = 0) then
  begin
    Memo1.Lines.Add(ssh.LastErrorText);
    Exit;
  end;
Memo1.Lines.Add(output);

ssh.Disconnect();