Issue reading the output of a process (cipher.exe)

Pejman 1

Reading output from process works fine. For example I run ping 4.2.2.4 and I can read output live and line by run. But for cipher /w:c: does not show the output until the end of thread.

    Private Sub RunApp()
        Dim Proc As New Process
        AddHandler Proc.OutputDataReceived, AddressOf Proc_OutputDataReceived
        AddHandler Proc.ErrorDataReceived, AddressOf Proc_ErrorDataReceived
        Dim startInfo As New ProcessStartInfo
        With startInfo
            .FileName = "ping"              REM "cipher"
            .Arguments = "4.2.2.4"          REM "/w:c:"
            .RedirectStandardOutput = True
            .RedirectStandardError = True
            .CreateNoWindow = True
            .UseShellExecute = False
        End With
        Proc.StartInfo = startInfo
        Proc.Start()
        Proc.BeginOutputReadLine()
        Proc.BeginErrorReadLine()
    End Sub

    Private Sub Proc_OutputDataReceived(sender As Object, e As DataReceivedEventArgs)
        If e.Data IsNot Nothing AndAlso Not String.IsNullOrEmpty(e.Data) Then
            Console.WriteLine(e.Data)
        End If
    End Sub

    Private Sub Proc_ErrorDataReceived(sender As Object, e As DataReceivedEventArgs)
        If e.Data IsNot Nothing AndAlso Not String.IsNullOrEmpty(e.Data) Then
            Console.WriteLine(e.Data)
        End If
    End Sub

Is there anything I forgot?

Xingyu Zhao-MSFT 5,361

Hi @Pejman ,

how can I read the output when a complete line has not yet been written?

Take a look at the following code:

        Dim baseStream As FileStream = TryCast(Proc.StandardOutput.BaseStream, FileStream)  
        Dim bytes As Byte() = Nothing  
        Dim lastRead As Integer = 0  
  
        Dim buffer As Byte() = New Byte(1) {}  
        Do  
            lastRead = baseStream.Read(buffer, 0, buffer.Length)  
            Console.Write(Encoding.Default.GetString(buffer))  
        Loop While lastRead > 0

Hope it could be helpful.

Pejman 1 Reputation point

2021-11-23T07:19:27.577+00:00

Thank you. This code works fine but does not show cipher.exe progress dots. Cipher sends dots consecutively, but this code can not read them. All characters are received except progress dots.

To remove as much data as possible, please close all other applications while running CIPHER /W.
Writing 0x00
....................................................................................................
Writing 0xFF

When it reaches the first dot of output progress, it gets stuck on line 7 and waits for the first character to arrive (W in Writing 0xFF).
Xingyu Zhao-MSFT 5,361 Reputation points

2021-11-24T02:54:36.683+00:00

Hi @Pejman ,
Check the following reference and see if it works for your problem.
Read Process StandardOutput before New Line Received
You can convert the code to vb .net.
Pejman 1 Reputation point

2021-11-24T10:56:26.45+00:00

Unfortunately not work for cipher.
Michael Taylor 51,346 Reputation points

2021-11-24T15:09:05.153+00:00

You may be stuck going to Win32 for this. I don't know if it'll be a better experience though. If you drop to Win32 then you can redirect the output to a pipe that you can then read the pipe. This is effectively what BeginOutputReadLine is doing but you can then call ReadFile directly. If it doesn't work in Win32 then it probably isn't going to work anywhere.

1 answer

Michael Taylor 51,346 Reputation points

2021-11-22T16:50:25.997+00:00

I suspect you're seeing the same behavior in both cases but it just isn't obvious. ping should return back almost instantly so probably by the time your RunApp function gets to the end the other process is already done. cipher on the other hand probably takes a while and so your runapp is finished before it gets done. In either case you are not blocking until the process completes so whoever calls RunApp is potentially running while the other process is still running in the background. If the current process is doing a lot of CPU work or writing to the console then they'll be fighting for resources.

You might consider switching to an async call and then blocking until the process completes if that is what you want to accomplish.

Note that console apps can write to the output/error stream however they want. Some processes may buffer calls until the end while others may write as they go along. You have no control over that behavior but running from the command prompt should make this obvious.
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Pejman 1 Reputation point

2021-11-22T17:03:05.857+00:00

There is no difference between ping and cipher. Cipher repeatedly sends progress points to the output. ــــ That this code can not read it.
Execute this command in the command prompt. You will find out for yourself.
cipher /w:c:

Michael Taylor 51,346 Reputation points

2021-11-22T17:21:34.157+00:00

They are different however. Watch how ping writes. It writes a line of text at a time. cipher on the other hand dumps some starting data and then writes progress dots on the screen. These are on the same line. As specified in the docs the output isn't provided until a line is written. So without knowing the exact output you're seeing I suspect you're getting a couple lines of output and then you're seeing nothing while the progress is running because it isn't writing a full line. It isn't until the progress indicator finishes that the newline is generated and then the output is provided to you.

Pejman 1 Reputation point

2021-11-22T17:36:20.31+00:00

You are right. So how can I read the output when a complete line has not yet been written?

Michael Taylor 51,346 Reputation points

2021-11-22T17:43:47.423+00:00

Good question. Those methods were added as convenience for the very common need to read the output stream from a process. But they are just wrappers around the underlying calls to read the output stream directly. Therefore if you need that kind of functionality then you'd need to basically do what those methods are doing instead. But this is a little tricky to get right so you'll want to weigh the options. Ultimately though you'll simply use the StandardOutput property directly instead of relying on the methods. You probably don't want to call ReadToEnd as that causes potential issues, which is why we have the methods. But you could call ReadAsync or more likely Peek to continually poll for data to read. You'll need to be careful that you don't eat up CPU cycles waiting though.

Pejman 1 Reputation point

2021-11-23T00:49:40.163+00:00

I was able to read the output byte by byte with the following code:

Proc.StartInfo = startInfo Proc.Start() Dim reader As StreamReader = Proc.StandardOutput While 1 REM Not Proc.HasExited Await Task.Delay(1) Dim buf() As Char = New Char(1) {} Dim l As Integer = Await reader.ReadAsync(buf, 0, buf.Length) For i As Integer = 0 To l - 1 Console.Write(buf(i)) Next End While

But the problem was still not solved.
When it reaches the first dot of output progress, it waits in line 7.
It seems that the dots of progress are not ordinary characters.

Michael Taylor 51,346 Reputation points

2021-11-23T15:29:18.967+00:00

It's possible that cipher is reusing the same line of the console. In a console app you can reset the position in the console window and overwrite an existing line. It was common for progress bar style UIs. I have no idea how this would work with the stream reader as it is literally overwriting the existing data. But I'd have to build an app to test that behavior to confirm.

Pejman 1 Reputation point

2021-11-23T15:48:32.59+00:00

Thank you
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Issue reading the output of a process (cipher.exe)

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