Poll an SSH Channel for Incoming Data

See more SSH Examples

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).

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final ssh = CkSsh();

  final sshPort = 22;
  try {
    ssh.connect('ssh.example.com', sshPort);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // 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.
  final password = 'mySshPassword';

  try {
    ssh.authenticatePw('mySshLogin', password);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final channelNum = ssh.openSessionChannel();
  if (channelNum < 0) {
    print(ssh.lastErrorText);
    return;
  }

  // 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.
  try {
    ssh.sendReqShell(channelNum);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    ssh.channelSendString(channelNum, 'date\n', 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Wait up to 3 seconds for channel data.
  final 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.
  final result = ssh.channelPoll(channelNum, pollTimeoutMs);
  if (result == -1) {
    print(ssh.lastErrorText);
    return;
  }

  if (result == -2) {
    print('No channel data arrived before the timeout.');
  }

  if (result == 0) {
    print('EOF or channel close was processed.  Buffered data may still remain.');
  }

  if (result > 0) {
    print('Total bytes buffered: $result');
  }

  final String output;
  try {
    output = ssh.getReceivedText(channelNum, 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(output);

  ssh.disconnect();
}