Read an SSH Channel with a Byte Threshold

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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).

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

begin
success := 0;

//  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 := 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,'cat /var/log/syslog' + #10,'utf-8');
if (success = 0) then
  begin
    Memo1.Lines.Add(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
    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();