Enable server-only operation and add server section to configs

- Fixed init_connections() to allow 0 connections for server-only mode
- All instances now require [server] section for bind socket
- Added test configs demonstrating server-only and client-with-server patterns
- Created run_two_instance_test.sh for manual handshake testing

src/etcp_connections.c

@@ -562,8 +562,10 @@ int init_connections(struct UTUN_INSTANCE* instance) {
         client = client->next;
     }
     
-    if (instance->connections_count == 0) {
-        DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "No connections initialized");
+    // If there are clients configured but no connections created, that's an error
+    // If there are no clients (server-only mode), 0 connections is OK (server will accept incoming)
+    if (instance->connections_count == 0 && config->clients != NULL) {
+        DEBUG_ERROR(DEBUG_CATEGORY_ETCP, "Clients configured but no connections initialized");
         return -1;
     }
     

tests/run_two_instance_test.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# Test script for ETCP connection establishment with real instances
+
+DIR=$(cd "$(dirname "$0")" && pwd)
+
+echo "=== ETCP Two-Instance Test ==="
+echo
+
+# Start server instance in background
+echo "Starting server instance..."
+$DIR/test_server_only &
+SERVER_PID=$!
+sleep 1
+
+# Start client instance
+echo "Starting client instance..."
+timeout 10 $DIR/test_server_only 2>&1
+
+# Cleanup
+kill $SERVER_PID 2>/dev/null
+wait $SERVER_PID 2>/dev/null
+
+echo
+echo "=== Test completed ==="

tests/test_server_only.conf

@@ -0,0 +1,10 @@
+[global]
+my_node_id=0x1111111111111111
+my_private_key=1313912e5d34768983b0e06530a48c77816d228a5b5605e1ab3dc443d107a3dc
+my_public_key=dde6cec8a9023339a758f60883ef41534d24a1ffdc09bbb787a5c24ddfd891e3092461835a97d37944c681fc6b2c1f5acde8ad192f7d2cdc9920aa0d3ff78e99
+tun_ip=10.99.0.1/24
+tun_ifname=tun99
+
+[server: test]
+addr=127.0.0.1:9001
+type=public