tree 8ac4a2c314ccf13b0653e34aa5b9376a4f6abdd9
parent 7871e2fd09acf3790cc292d955cdd8fee86f2fdb
author Philip Zeyliger <philip@bold.dev> 1748622775 -0700
committer Philip Zeyliger <philip@bold.dev> 1748622810 -0700

loop/server: enable SSH reverse port forwarding

~~~~

vibe-coded but tested manually with

	$python3 -mhttp.server 8000 &
	[1] 25986
	Serving HTTP on :: port 8000 (http://[::]:8000/) ...

	$ssh -R 8000:localhost:8000 sketch-241k-9zzx-gcbc-k4fs curl --silent http://localhost:8000/ | head -n 3
	::1 - - [30/May/2025 09:32:44] "GET / HTTP/1.1" 200 -
	<!DOCTYPE HTML>
	<html lang="en">
	<head>

~~~~

Implement ReversePortForwardingCallback in SSH server configuration to
allow reverse port forwarding connections from clients.

Changes include:

1. SSH Server Configuration Enhancement:
   - Added ReversePortForwardingCallback to ssh.Server struct
   - Callback allows all reverse port forwarding requests (returns true)
   - Consistent with existing LocalPortForwardingCallback behavior
   - Includes debug logging for reverse forwarding requests

Technical Implementation:

The SSH server already had the necessary infrastructure for port forwarding:
- ForwardedTCPHandler for handling forwarding requests
- RequestHandlers for 'tcpip-forward' and 'cancel-tcpip-forward'
- LocalPortForwardingCallback for client-to-server forwarding

This change adds the missing ReversePortForwardingCallback that enables
server-to-client port forwarding (reverse tunneling). The callback follows
the same permissive pattern as the local forwarding callback, allowing
all reverse forwarding requests while logging them for debugging.

Without this callback, the SSH library defaults to denying all reverse
port forwarding requests, preventing clients from establishing reverse
tunnels through the SSH connection.

Benefits:
- Enables full bidirectional port forwarding capabilities
- Maintains consistent logging and debugging for both forwarding types
- Follows established patterns in the existing codebase
- No breaking changes to existing SSH functionality

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: s9bc98f6471e2ec4dk