PowerShell and Telnet Integration Outputs Junk Chars

Question

I have tried to get PowerShell automation for Telnet connecting to Windows Server 2012 R2, Ubuntu 16.04 and Windows XP SP3 and all servers are throwing junk characters as output.

I was going through rfc854 but I could not get this done.

Could you please help me on how to resolve this issue.

Below code would try to connect Telnet server with credentials and output dir list.

Code

param (
    [string] $terminalServer = "192.168.19.131",
    [int] $port = 23,
    [string] $username = "username",
    [string] $password = "password",
    [int] $commandDelay = 1000,
    [string] $output = ""
)

function GetOutput {
    ## Create a buffer to receive the response
    $buffer = new-object System.Byte[] 1024
    $encoding = new-object System.Text.AsciiEncoding
    $outputBuffer = ""
    $foundMore = $false
    ## Read all the data available from the stream, writing it to the
    ## output buffer when done.
    do {
        ## Allow data to buffer for a bit
        start-sleep -m 1000
        ## Read what data is available
        $foundmore = $false
        $stream.ReadTimeout = 2000
        do {
            try {
            $read = $stream.Read($buffer, 0, 1024)
                if($read -gt 0) {
                    $foundmore = $true
                        $outputBuffer += ($encoding.GetString($buffer, 0, $read))
                }
            } catch { $foundMore = $false; $read = 0 }
        } while($read -gt 0)

    } while($foundmore)

    $outputBuffer
}

$output = ""

write-host "Connecting to $terminalServer on port $port..."
trap { Write-Error "Could not connect to the server: $_"; exit }

$socket = new-object System.Net.Sockets.TcpClient($terminalServer, $port)
write-host "Connected. `n"
$stream = $socket.GetStream()
$writer = new-object System.IO.StreamWriter $stream

## Receive the output that has buffered so far
$SCRIPT:output += GetOutput

$writer.WriteLine($username)
$writer.Flush()
Start-Sleep -m $commandDelay

$SCRIPT:output += GetOutput

$writer.WriteLine($password)
$writer.Flush()
Start-Sleep -m $commandDelay

$SCRIPT:output += GetOutput

$writer.WriteLine("dir")
$writer.Flush()
Start-Sleep -m $commandDelay

$SCRIPT:output += GetOutput

$writer.WriteLine("exit")
$writer.Flush()
Start-Sleep -m $commandDelay

## Close the streams
$writer.Close()
$stream.Close()

write-host "All streams are closed. The final output is"
$output

Output

D:\Tools\T24\PowerShell>powershell .\telnet_test.ps1
Connecting to 192.168.19.131 on port 23...
Connected.

All streams are closed. The final output is
??%??????'???? ??

The "junk" is likely to be a sequence of Telnet control characters. Instead of raw TCP, consider using some readily available Telnet library. — vonPryz, Sep 06 '17 at 06:51
Thanks @vonPryz. Any specific PowerShell library you recommend? I have tried few but didn’t help. — digidhamu, Sep 06 '17 at 07:23
Unfortunately, no. There are quite a few mentioned in [old a question](https://stackoverflow.com/q/390188). — vonPryz, Sep 06 '17 at 07:28

score 0 · Answer 1 · answered Sep 07 '17 at 04:57

0

I have tried with jBASE Telnetd Server Version 4.1.1 on Windows Server 2012 R2 and perfectly listing directory.

So, with Windows version of Telnet requires some more manipulation as per rfc854 implementation.

answered Sep 07 '17 at 04:57

digidhamu

717
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PowerShell and Telnet Integration Outputs Junk Chars

1 Answers1