NetVM: CDP via userspace relay (REDIRECT to loopback did not establish)

bin/netvm-cdp-relay.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python3
+"""TCP relay: listen on the netns veth IP:CDP_PORT, forward to 127.0.0.1:CDP_PORT.
+Chromium binds DevTools to loopback only; this exposes it on the veth IP for
+the host (and SSH-forwarded operators). Runs inside the netns. No dependencies.
+Usage: netvm-cdp-relay.py <listen_ip> <listen_port> <target_ip> <target_port>
+"""
+import socket, threading, sys
+
+def pipe(src, dst):
+    try:
+        while True:
+            data = src.recv(65536)
+            if not data:
+                break
+            dst.sendall(data)
+    except OSError:
+        pass
+    finally:
+        for s in (src, dst):
+            try: s.shutdown(socket.SHUT_RDWR)
+            except OSError: pass
+            s.close()
+
+def handle(client, target):
+    try:
+        upstream = socket.create_connection(target, timeout=10)
+    except OSError:
+        client.close()
+        return
+    threading.Thread(target=pipe, args=(client, upstream), daemon=True).start()
+    pipe(upstream, client)
+
+def main():
+    listen_ip, listen_port, target_ip, target_port = sys.argv[1], int(sys.argv[2]), sys.argv[3], int(sys.argv[4])
+    srv = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    srv.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
+    srv.bind((listen_ip, listen_port))
+    srv.listen(16)
+    while True:
+        client, _ = srv.accept()
+        threading.Thread(target=handle, args=(client, (target_ip, target_port)), daemon=True).start()
+
+if __name__ == "__main__":
+    main()

bin/netvm-node-down.sh

@@ -5,6 +5,8 @@ SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
 . "$SCRIPT_DIR/netvm-names.sh"
 netvm_names "${1:?usage: netvm-node-down.sh <node>}"
 nsexec() { ip netns exec "$NETNS" "$@"; }
+PIDFILE="/run/netvm-${NODE}-cdp-relay.pid"
+if [ -f "$PIDFILE" ]; then kill "$(cat "$PIDFILE")" 2>/dev/null || true; rm -f "$PIDFILE"; fi
 nsexec ip link del "$WG" 2>/dev/null || true      # inside netns first
 ip link del "$VETH" 2>/dev/null || true           # also drops the netns-side peer
 ip link del "$WG" 2>/dev/null || true            # stray host-side copy

bin/netvm-node-up.sh

@@ -58,13 +58,18 @@ nsexec ip link set "$WG" up
 nsexec ip route replace default dev "$WG"
 nsexec ip -6 route replace default dev "$WG" 2>/dev/null || true
 
-# CDP bridge: chromium binds DevTools to loopback only; redirect the veth
+# CDP bridge: chromium binds DevTools to loopback only. A tiny TCP relay
-# IP:CDP_PORT there so the host (and SSH-forwarded operators) can reach it.
+# listens on the veth IP and forwards to loopback (empirically reliable;
-# (netns iptables is namespaced; rules vanish with the netns on down.)
+# iptables REDIRECT to 127.0.0.1 did not establish). Supervised via pidfile.
-nsexec sysctl -qw net.ipv4.conf.all.route_localnet=1
+PIDFILE="/run/netvm-${NODE}-cdp-relay.pid"
-nsexec sysctl -qw "net.ipv4.conf.${VPEER}.route_localnet=1"
+if [ -f "$PIDFILE" ] && kill -0 "$(cat "$PIDFILE")" 2>/dev/null; then
-nsexec iptables -t nat -C PREROUTING -d "$PEER_IP" -p tcp --dport "$CDP_PORT" -j REDIRECT --to-port "$CDP_PORT" 2>/dev/null || \
+  echo "cdp relay already running"
-nsexec iptables -t nat -A PREROUTING -d "$PEER_IP" -p tcp --dport "$CDP_PORT" -j REDIRECT --to-port "$CDP_PORT"
+else
+  nsexec python3 "$SCRIPT_DIR/netvm-cdp-relay.py" "$PEER_IP" "$CDP_PORT" 127.0.0.1 "$CDP_PORT" \
+    >/dev/null 2>&1 &
+  echo $! > "$PIDFILE"
+  echo "cdp relay started ($PEER_IP:$CDP_PORT -> 127.0.0.1:$CDP_PORT)"
+fi
 
 # wait for handshake (first one can take ~10s)
 HS=""