Cool PowerShell Script Replicates Telnet

Lee Holmes has a cool script to reproduce telnet-like functionality via the TcpClient object in PowerShell.

## Connect-Computer.ps1 
## Interact with a service on a remote TCP port 
param( 
    [string] $remoteHost = "localhost", 
    [int] $port = 23
     ) 

try
{
    ## Open the socket, and connect to the computer on the specified port 
    write-host "Connecting to $remoteHost on port $port" 
    $socket = new-object System.Net.Sockets.TcpClient($remoteHost, $port) 
    if($socket -eq $null) { return; } 

    $stream = $socket.GetStream() 
    $writer = new-object System.IO.StreamWriter($stream) 

    $buffer = new-object System.Byte[] 1024 
    $encoding = new-object System.Text.AsciiEncoding 

    while($true) 
    { 
       ## Allow data to buffer for a bit 
       start-sleep -m 500 

       ## Read all the data available from the stream, writing it to the 
       ## screen when done. 
       while($stream.DataAvailable)  
       {  
          $read = $stream.Read($buffer, 0, 1024)    
          write-host -n ($encoding.GetString($buffer, 0, $read))  
       } 

       ## Read the user's command, quitting if they hit ^D 
       $command = read-host 
      
       ## Write their command to the remote host      
       $writer.WriteLine($command) 
       $writer.Flush() 
    } 
}
finally
{
    ## Close the streams 
    $writer.Close() 
    $stream.Close()
}

This solves the problem of telnet.exe crashing conhost.exe when using Console2.

Update

I tweaked Lee’s code to use try/finally which obviates the need for a special escape sequence to clean up the TCP resources.

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WorkAround: Console2 + Telnet.exe on Windows 7 Crashes ConHost.exe

conshost-croak

Entering the Windows telnet.exe prompt mode causes the shell process underneath Console2 to crash on Windows 7. You can reproduce this by just invoking telnet with no arguments in a Console2 session. An alternate route to hit this is exiting a telnet session with CTRL+].

The symptom is Console2 freezing because it is no longer getting text from its slaved native console followed up with a crash dialog for conhost.exe and whetever your shell was.

Unhandled exception at 0xffdd1df9 in conhost.exe: 0xC0000005: Access violation reading location 0x0000000003385460.>    conhost.exe!SB_StreamWriteToScreenBuffer()  + 0x61 bytes   

A workaround is to launch telnet into a separate conhost.exe window.

#force telnet.exe to start in its own console window. 
function telnet { start $env:SystemRoot\System32\telnet.exe $args }

Or use putty –P port –telnet host as an alternative to telnet.exe. (I can’t get plink.exe to be interactive with telnet for me.)

Update

Unless you need something nifty that telnet.exe is doing, a more elegant solution is to Lee Holmes’ Connect-Computer.ps1 PowerShell script as a telnet replacement.

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