Dart

Multiple SendReqExec on the Same Connection

Demonstrates running a series of commands on one SSH connection using SendReqExec. Each exec request requires its own logical channel — this is not a separate SSH connection, just a new session channel on the existing one.

Background: An SSH session channel is single-use for an exec request: once the command runs and the server closes the channel, that channel cannot be reused. Opening a fresh channel per command is cheap, since the expensive work — the TCP connection, key exchange, and authentication — is done once and shared. This is why running ten commands over one connection is far faster than connecting ten times.

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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  // Demonstrates running a series of commands on one SSH connection using SendReqExec.  Each exec
  // request requires its own logical channel.  This is not a new SSH connection -- it is simply a
  // new session channel on the existing one.

  final ssh = CkSsh();

  final hostname = 'ssh.example.com';
  final port = 22;
  try {
    ssh.connect(hostname, port);
  } 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;
  }

  // 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;

  // ---- 1st command, on its own session channel ----
  var channelNum = ssh.openSessionChannel();
  if (channelNum < 0) {
    print(ssh.lastErrorText);
    return;
  }

  try {
    ssh.sendReqExec(channelNum, 'ls -al');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

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

  print(cmdOutput);
  print('----');

  // ---- 2nd command, on a NEW session channel over the same connection ----
  channelNum = ssh.openSessionChannel();
  if (channelNum < 0) {
    print(ssh.lastErrorText);
    return;
  }

  try {
    ssh.sendReqExec(channelNum, 'nslookup chilkatsoft.com');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

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

  print(cmdOutput);

  ssh.disconnect();
}