Powershell - after inputting to stdin capturing stdout/stderr no longer works - powershell

Question

In a pretty restricted environment I'm basically only allowed to use Powershell + Plink if I want to automate some tasks.
I want to create a function that:
shows the output as it arrives if required
captures all output (stdout and stderr) to make it available later for further parsing or logging to console/file/whatever
inputs a password automatically
Unfortunately after the line where I input the password output capture stops. It used to work when I was only capturing stdout. After capturing stderr as well, no more luck.
The code:
function BaseRun {
param ($command, $arguments, $output = "Console")
$procInfo = New-Object System.Diagnostics.ProcessStartInfo
$procInfo.RedirectStandardOutput = $true
$procInfo.RedirectStandardError = $true
$procInfo.RedirectStandardInput = $true
$procInfo.FileName = $command
$procInfo.Arguments = $arguments
$procInfo.UseShellExecute = $false
$process = New-Object System.Diagnostics.Process
$process.StartInfo = $procInfo
[void]$process.Start()
$outputStream = $process.StandardOutput
$errorStream = $process.StandardError
$inputStream = $process.StandardInput
$outputBuffer = New-Object System.Text.StringBuilder
Start-Sleep -m 2000
$inputStream.Write("${env:password}`n")
while (-not $process.HasExited) {
do {
$outputLine = $outputStream.ReadLine()
$errorLine = $errorStream.ReadLine()
[void]$outputBuffer.Append("$outputLine`n")
if (($output -eq "All") -or ($output -eq "Console")) {
Write-Host "$outputLine"
Write-Host "$errorLine"
}
} while (($outputLine -ne $null) -and ($errorLine -ne $null))
}
return $outputBuffer.ToString()
}

Answer 1

Based on #w0xx0m's and #Martin Prikryl's help I managed to make this working solution:
Register-ObjectEvent -InputObject $process `
-EventName OutputDataReceived -SourceIdentifier processOutputDataReceived `
-Action {
$data = $EventArgs.data
if($data -ne $null) { Write-Host $data }
} | Out-Null
Register-ObjectEvent -InputObject $process `
-EventName ErrorDataReceived -SourceIdentifier processErrorDataReceived `
-Action {
$data = $EventArgs.data
if($data -ne $null) { Write-Host $data }
} | Out-Null
[void]$process.Start()
$process.BeginOutputReadLine()
$process.BeginErrorReadLine()
$inputStream = $process.StandardInput
Start-Sleep -m 2000
$inputStream.Write("${env:password}`n")
$process.WaitForExit()
Unregister-Event -SourceIdentifier processOutputDataReceived
Unregister-Event -SourceIdentifier processErrorDataReceived
$inputStream.Close()
For brevity I've removed the process launch section (it's the same as the one from above) and the data processing (in the example I just Write-Host it).

Answer 2

When you are reading both stdout and stderr, you cannot not use the ReadLine.
First, if there's only stderr output and no stdout, the $outputStream.ReadLine() never returns and you never get to the $errorStream.ReadLine().
A bigger problem is, that there's only a limited buffer in Windows for the outputs. So, when there's a lot of stderr before a complete stdout line is produced, the stderr buffer fills up and the applications (Plink) stops on the next attempt to write to stderr, waiting for the stderr buffer to be consumed. What it never does, as you keep waiting on a wrong stdout buffer. A deadlock.
You have to use a simple Read and never synchronously wait, when there's no output available.