Hey everyone! I've been using Ncat for a while after switching from Netcat, and I'm running into a bit of an issue. I set up a simple server command with Ncat as follows: `ncat -l 5000 -k -e 'server_script'`. The `server_script` is just a small script that reads input and echoes it back to the client. It works fine, but after the client sends a line, the connection doesn't close automatically as I expected. Instead, I have to hit Enter a couple of times to finally trigger a "Broken Pipe" message before it disconnects. How can I modify the script or the command to ensure that it disconnects right after the script finishes? Thanks!
3 Answers
What happens if you modify your server script to not wait for input and just echo some text? Does that change the behavior at all? It could help determine if Ncat is retaining the connection for some other reason.
Have you checked if your client is configuring the end-of-line characters correctly? Sometimes extra characters can keep the connection open. Try using Ctrl-M (cr) or Ctrl-J (lf) to see if that changes anything. It's also worth confirming that your server script works as intended when you run it directly in the shell without Ncat, which sounds like it does, based on your description!
Yes, I’ve tried Ctrl-M and Ctrl-J, but it still doesn’t auto-disconnect. The script runs perfectly fine when executed directly in the shell, so it seems to be an Ncat-related issue.
If the script is validating correctly in the shell but not with Ncat, there may be differences in how Ncat handles the connection state. Let us know if you try a different client!
The reason the connection doesn't close automatically is due to how TCP handles connection teardowns. When your script finishes, the server sends a FIN signal, but if the client hasn't indicated that it's done sending data, it'll leave the connection half-closed. You can send an EOF signal from the client side by using Ctrl-D after you're done sending data. This should allow Ncat to properly close the connection. If that's not working for you, you might want to consider switching to Socat, which behaves differently and may solve your issue.
Sounds like a solid plan! Socat is known for being more versatile, so it might just handle your requirements better.
Thanks for the suggestion! I'll give Socat a shot and report back on how it goes.
I haven’t tried that yet! I’ll experiment with that approach and see if it makes any difference.