# ETCP Monitor - Implementation Summary

## Overview
ETCP Monitor is a Windows GUI utility for real-time monitoring of ETCP connections in uTun.

## Architecture

### Protocol (Binary)
- **Format**: `[2 bytes: size] [1 byte: type] [payload...]`
- **Period**: 100ms updates
- **Transport**: TCP socket

### Message Types
**Client → Server:**
- `0x01` - Request connection list
- `0x02` - Select connection by peer_node_id
- `0x03` - Request metrics
- `0x04` - Disconnect

**Server → Client:**
- `0x81` - Connection list response
- `0x82` - Metrics response (ETCP + TUN + Links)
- `0xFF` - Error response

## Files Created

### Protocol (Shared)
- `tools/etcpmon/etcpmon_protocol.h` - Protocol definitions and structures

### Server (uTun)
- `src/control_server.h` - Control server interface
- `src/control_server.c` - TCP server implementation
- Modified `src/utun_instance.c` - Integration with uTun lifecycle
- Modified `src/Makefile.am` - Added control_server.c to build
- Modified `lib/debug_config.h` - Added DEBUG_CATEGORY_CONTROL

### Client (Windows GUI)
- `tools/etcpmon/etcpmon_client.h/c` - Network layer (Winsock)
- `tools/etcpmon/etcpmon_gui.h/c` - WinAPI GUI implementation
- `tools/etcpmon/etcpmon_main.c` - Entry point
- `tools/etcpmon/Makefile.mingw` - MinGW build
- `tools/etcpmon/build.bat` - Windows build script
- `tools/etcpmon/build.sh` - Unix build script
- `tools/etcpmon/clean.bat` - Clean script
- `tools/etcpmon/README.md` - Documentation

### Test
- `tests/test_control_server.c` - Integration test for control server protocol

### Library Fix
- `lib/u_async.c` - Modified to use select() on Windows instead of WSAPoll

## Build Instructions

### Windows (Recommended)
```cmd
cd tools\etcpmon
build.bat
```

### Unix/MinGW
```bash
cd tools/etcpmon
bash build.sh
```

## Usage

### 1. Configure uTun
Add to `utun.conf`:
```ini
control_ip=127.0.0.1
control_port=9090
```

### 2. Start uTun
```bash
./utun
```

### 3. Start ETCP Monitor
```cmd
etcpmon.exe
```

### 4. Connect
- Enter server IP:port (default: 127.0.0.1:9090)
- Click "Connect"
- Select connection from list
- View real-time metrics

## Metrics Displayed

### ETCP Connection
- RTT (last, avg 10, avg 100)
- Jitter
- Bytes sent total
- Retransmission count
- ACK count
- Unacked bytes
- Links count

### TUN Interface
- Bytes read/written
- Packets read/written
- Read/write errors

### Links (per link)
- Status (UP/DOWN)
- Encrypt/decrypt errors
- Send/receive errors
- Total encrypted/decrypted bytes
- Bandwidth (Kbps)
- NAT changes count

## Technical Details

### Windows select() Implementation
On Windows, the uasync library now uses `select()` instead of `WSAPoll()` for socket monitoring. This resolves issues with accepted TCP sockets that caused WSAPoll to fail with error 10022 (WSAEINVAL).

**Changes in `lib/u_async.c`:**
- Added Windows-specific code path using `select()`
- Maintains compatibility with Linux (uses `poll()`)
- Properly handles both regular FDs and socket_t types

### Binary Protocol
The protocol uses fixed-size binary structures for efficient communication:
- Header: 3 bytes (2 size + 1 type)
- Connection list item: 40 bytes (8 peer_id + 32 name)
- ETCP metrics: 40 bytes
- Link metrics: 32 bytes per link
- TUN metrics: 24 bytes

## Testing

### Unit Test
```bash
cd tests
./test_control_server
```

Expected output:
```
================================
Control Server Protocol Test
================================

[TEST] Setting up mock data...
[TEST] Mock data ready (1 conn, 2 links)
[TEST] Starting control server on port 19090...
[TEST] Control server started ✓
[TEST] Starting client thread...
[TEST] Running event loop...

[CLIENT] Connecting to 127.0.0.1:19090...
[CLIENT] Connected
[CLIENT] Sending CMD_LIST_CONN...
[CLIENT] Waiting for response...
[CLIENT] Received connection list: 1 connection(s)
[CLIENT] Connection verified: peer_id=0x1234567890ABCDEF ✓
[CLIENT] All tests passed ✓

[TEST] Cleaning up...

================================
[PASS] All tests passed!
================================
```

## License
See main project LICENSE file.