There is a long running script script.sh
on a remote Linux machine. I need to start it and monitor it's activity in real time. The script during it's activity may output to stdout
and stderr
. I am searching for a way to capture both of the streams.
I use Renci SSH.NET to upload script.sh
and start it, so it would be great to see a solution bounded to this library. In my mind the perfect solution is the new method:
var realTimeScreen= ...;
var commandExecutionStatus = sshClient.RunCommandAsync(
command: './script.sh',
stdoutEventHandler: stdoutString => realTimeScreen.UpdateStdout(stdString)
stderrEventHandler: stderrString => realTimeScreen.UpdateStderr(stderrString));
...
commandExecutionStatus.ContinueWith(monitoringTask =>
{
if (monitoringTask.Completed)
{
realTimeScreen.Finish();
}
});
Use SshClient.CreateCommand
method. It returns SshCommand
instance.
The SshCommand
class has OutputStream
(and Result
) for stdout and ExtendedOutputStream
for stderr.
See SshCommandTest.cs
:
public void Test_Execute_ExtendedOutputStream()
{
var host = Resources.HOST;
var username = Resources.USERNAME;
var password = Resources.PASSWORD;
using (var client = new SshClient(host, username, password))
{
#region Example SshCommand CreateCommand Execute ExtendedOutputStream
client.Connect();
var cmd = client.CreateCommand("echo 12345; echo 654321 >&2");
var result = cmd.Execute();
Console.Write(result);
var reader = new StreamReader(cmd.ExtendedOutputStream);
Console.WriteLine("DEBUG:");
Console.Write(reader.ReadToEnd());
client.Disconnect();
#endregion
Assert.Inconclusive();
}
}
See also a full code for similar WinForms question Execute long time command in SSH.NET and display the results continuously in TextBox.
So, here is the solution I came up with. Of course, it can be improved, so it is open to critique.
I used
await Dispatcher.Yield(DispatcherPriority.ApplicationIdle);
instead of Task.Yield()
because Task.Yield()
will make continuation a higher priority than GUI events, but, as a bad consequence, it demands your application to use WindowsBase.dll
.
public static class SshCommandExtensions
{
public static async Task ExecuteAsync(
this SshCommand sshCommand,
IProgress<ScriptOutputLine> progress,
CancellationToken cancellationToken)
{
var asyncResult = sshCommand.BeginExecute();
var stdoutStreamReader = new StreamReader(sshCommand.OutputStream);
var stderrStreamReader = new StreamReader(sshCommand.ExtendedOutputStream);
while (!asyncResult.IsCompleted)
{
await CheckOutputAndReportProgress(
sshCommand,
stdoutStreamReader,
stderrStreamReader,
progress,
cancellationToken);
await Dispatcher.Yield(DispatcherPriority.ApplicationIdle);
}
sshCommand.EndExecute(asyncResult);
await CheckOutputAndReportProgress(
sshCommand,
stdoutStreamReader,
stderrStreamReader,
progress,
cancellationToken);
}
private static async Task CheckOutputAndReportProgress(
SshCommand sshCommand,
TextReader stdoutStreamReader,
TextReader stderrStreamReader,
IProgress<ScriptOutputLine> progress,
CancellationToken cancellationToken)
{
if (cancellationToken.IsCancellationRequested)
{
sshCommand.CancelAsync();
}
cancellationToken.ThrowIfCancellationRequested();
await CheckStdoutAndReportProgressAsync(stdoutStreamReader, progress);
await CheckStderrAndReportProgressAsync(stderrStreamReader, progress);
}
private static async Task CheckStdoutAndReportProgressAsync(
TextReader stdoutStreamReader,
IProgress<ScriptOutputLine> stdoutProgress)
{
var stdoutLine = await stdoutStreamReader.ReadToEndAsync();
if (!string.IsNullOrEmpty(stdoutLine))
{
stdoutProgress.Report(new ScriptOutputLine(
line: stdoutLine,
isErrorLine: false));
}
}
private static async Task CheckStderrAndReportProgressAsync(
TextReader stderrStreamReader,
IProgress<ScriptOutputLine> stderrProgress)
{
var stderrLine = await stderrStreamReader.ReadToEndAsync();
if (!string.IsNullOrEmpty(stderrLine))
{
stderrProgress.Report(new ScriptOutputLine(
line: stderrLine,
isErrorLine: true));
}
}
}
public class ScriptOutputLine
{
public ScriptOutputLine(string line, bool isErrorLine)
{
Line = line;
IsErrorLine = isErrorLine;
}
public string Line { get; private set; }
public bool IsErrorLine { get; private set; }
}
In addition to Wojtpl2's answer. For commands like "tail -f" one of the streamer tasks will lock on ReadLine method:
var stderrLine = await streamReader.ReadLineAsync();
To overcome this, we need to pass token to streamReader with extension method:
public static Task<T> WithCancellation<T>(this Task<T> task, CancellationToken cancellationToken)
{
return task.IsCompleted // fast-path optimization
? task
: task.ContinueWith(
completedTask => completedTask.GetAwaiter().GetResult(),
cancellationToken,
TaskContinuationOptions.ExecuteSynchronously,
TaskScheduler.Default);
}
thx to Can I cancel StreamReader.ReadLineAsync with a CancellationToken?
and use it like this:
var stderrLine = await streamReader.ReadToEndAsync().WithCancellation(cancellationToken);
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