# Network Switching Improvements for HMAC File Server

## ✅ Implementation Complete

The network resilience features have been successfully implemented and are ready to use!

### 🚀 Quick Start

1. **Build the enhanced server:**
   ```bash
   ./buildgo.sh
   ```

2. **Use the network-resilient configuration:**
   ```bash
   cp config-network-resilience.toml config.toml
   # Edit config.toml with your settings
   ```

3. **Start the server:**
   ```bash
   ./hmac-file-server --config config.toml
   ```

4. **Test the features:**
   ```bash
   ./test_network_resilience.sh
   ```

## 🔧 What's Been Fixed

### ✅ Implementation Status

### ✅ Implementation Status

| Feature | Status | Description |
|---------|--------|-------------|
| **Chunked/Resumable Uploads** | ✅ **IMPLEMENTED** | 5MB chunks, survives network interruptions |
| **Network Change Detection** | ✅ **IMPLEMENTED** | Monitors interfaces, pauses/resumes uploads |
| **Session Persistence** | ✅ **IMPLEMENTED** | Redis or disk storage, 24h default timeout |
| **Enhanced Timeouts** | ✅ **IMPLEMENTED** | 5-minute read/write, 10-minute idle |
| **Retry Logic** | ✅ **IMPLEMENTED** | Exponential backoff with jitter |
| **Backward Compatibility** | ✅ **GUARANTEED** | Zero changes to existing upload handlers |

### 📂 New Files Added

- `cmd/server/upload_session.go` - Session management and persistence
- `cmd/server/network_resilience.go` - Network monitoring and pause/resume
- `cmd/server/chunked_upload_handler.go` - New chunked upload endpoint
- `cmd/server/integration.go` - Non-intrusive integration layer
- `config-network-resilience.toml` - Ready-to-use configuration
- `test_network_resilience.sh` - Automated testing script

### 🌐 New API Endpoints

| Endpoint | Method | Purpose |
|----------|--------|---------|
| `/chunked-upload` | POST | Start new chunked upload session |
| `/chunked-upload` | PUT | Upload individual chunks |
| `/upload-status` | GET | Check upload progress |
| `/upload` | POST | Traditional uploads (unchanged) |

## 📱 Network Switching Benefits

### Before (Problems Fixed)
- ❌ Upload fails completely on network interruption
- ❌ Progress lost when switching WiFi/WLAN  
- ❌ Large files problematic on mobile networks
- ❌ No recovery from connection drops

### After (Solutions Implemented)  
- ✅ **Seamless network switching** - uploads pause and resume automatically
- ✅ **Progress preservation** - no lost data during interruptions
- ✅ **Mobile optimized** - 5MB chunks perfect for cellular/WiFi
- ✅ **Intelligent retry** - exponential backoff handles temporary failures
- ✅ **Session persistence** - survives server restarts

## 📋 Usage Examples

### Traditional Upload (Unchanged)
```bash
curl -X POST -H "X-Signature: HMAC" -F 'file=@document.pdf' http://localhost:8080/upload
```

### New Chunked Upload
```bash
# 1. Start session
curl -X POST \
  -H "X-Filename: large_video.mp4" \
  -H "X-Total-Size: 104857600" \
  -H "X-Signature: HMAC" \
  http://localhost:8080/chunked-upload

# 2. Upload chunks (automatically handles network switches)
curl -X PUT \
  -H "X-Upload-Session-ID: session_123" \
  -H "X-Chunk-Number: 0" \
  --data-binary @chunk_0.bin \
  http://localhost:8080/chunked-upload

# 3. Check progress
curl "http://localhost:8080/upload-status?session_id=session_123"
```

## ⚙️ Configuration

Essential settings for network resilience:

```toml
[server]
networkevents = true              # Enable network monitoring

[uploads]  
chunkeduploadsenabled = true      # Enable chunked uploads
chunksize = "5MB"                 # Optimal for mobile
sessiontimeout = "24h"            # Session persistence

[timeouts]
readtimeout = "300s"              # 5 minutes for mobile
writetimeout = "300s"             # 5 minutes for slow networks
idletimeout = "600s"              # 10 minutes keep-alive
```

## 🔨 Build & Deploy

### Build Process
```bash
# Automatic build with network resilience detection
./buildgo.sh

# Output confirms features are included:
# [INFO] Found network resilience: upload_session.go
# [INFO] Found network resilience: network_resilience.go  
# [INFO] Found network resilience: chunked_upload_handler.go
# [INFO] Found network resilience: integration.go
# [BUILD] Build successful! Binary created: ./hmac-file-server
```

### Testing
```bash
# Comprehensive feature testing
./test_network_resilience.sh

# Expected output:
# ✅ Traditional upload works
# ✅ Chunked upload session creation works  
# ✅ Upload status endpoint works
# ✅ Health endpoint works
# ✅ Metrics endpoint works
```

## 🎯 Perfect for Your Use Case

This implementation specifically solves your **notebook network switching** problem:

1. **WLAN ↔ WiFi Switching**: Uploads automatically pause during network changes and resume when stable
2. **Mobile-Friendly**: 5MB chunks work well over cellular and WiFi connections  
3. **Android/iOS Compatible**: HTTP-based solution works with any mobile platform
4. **Zero Disruption**: Existing users see no changes, new users get enhanced reliability
5. **Production Ready**: Full session persistence, monitoring, and error handling

Your users can now upload large files from notebooks/mobile devices without worrying about network switching interrupting their transfers! 🚀