Smart Download

Turbo CDN's smart download mode automatically selects the best download method.

Overview

Smart download is the default mode in Turbo CDN. It automatically:

1. Tests direct download performance
2. Tests CDN mirror performance
3. Compares results
4. Selects the fastest option
5. Downloads using the optimal method

How It Works

Decision Flow

┌─────────────────────────────────────────────────────────────┐
│                    Smart Download Mode                       │
├─────────────────────────────────────────────────────────────┤
│  1. URL Analysis                                             │
│     └─ Determine if CDN optimization is available           │
│                                                              │
│  2. Parallel Testing                                         │
│     ├─ Test direct URL (HEAD request)                       │
│     └─ Test CDN mirrors (HEAD requests)                     │
│                                                              │
│  3. Performance Comparison                                   │
│     ├─ Compare latencies                                    │
│     └─ Factor in historical performance                     │
│                                                              │
│  4. Method Selection                                         │
│     ├─ If CDN is 20%+ faster → Use CDN                      │
│     └─ Otherwise → Use direct                               │
│                                                              │
│  5. Download Execution                                       │
│     └─ Download with selected method                        │
└─────────────────────────────────────────────────────────────┘

Usage

CLI (Default)

# Smart mode is the default
turbo-cdn dl "https://github.com/user/repo/releases/download/v1.0/file.zip"

# Explicitly enable smart mode (same as default)
turbo-cdn dl "https://github.com/user/repo/releases/download/v1.0/file.zip" --smart

# Verbose output shows decision process
turbo-cdn dl "https://github.com/user/repo/releases/download/v1.0/file.zip" --verbose

Library

use turbo_cdn::*;

#[tokio::main]
async fn main() -> turbo_cdn::Result<()> {
    let downloader = TurboCdn::new().await?;
    
    // Smart download (default behavior)
    let result = downloader.download_smart("https://github.com/user/repo/releases/download/v1.0/file.zip").await?;
    
    // With verbose output
    let result = downloader.download_smart_with_verbose(
        "https://github.com/user/repo/releases/download/v1.0/file.zip",
        true  // verbose
    ).await?;
    
    Ok(())
}

Download Modes

Smart Mode (Default)

Automatically selects the best method:

turbo-cdn dl "https://example.com/file.zip"

Direct Mode

Bypasses all optimization, downloads directly from source:

turbo-cdn dl "https://example.com/file.zip" --no-cdn

let result = downloader.download_direct_from_url("https://example.com/file.zip").await?;

CDN Mode

Forces CDN optimization (skips comparison):

turbo-cdn dl "https://example.com/file.zip" --force-cdn

let result = downloader.download_from_url("https://example.com/file.zip").await?;

Decision Criteria

When CDN is Selected

• CDN latency is 20% or more faster than direct
• Direct URL is unreachable or slow
• Historical data shows CDN performs better

When Direct is Selected

• Direct URL is fast (< 100ms latency)
• CDN provides minimal improvement (< 20%)
• No CDN mirrors available for the URL

Verbose Output

With --verbose, you can see the decision process:

🧠 Smart Download (Auto-Select Best Method) - Default Mode
=========================================================
Source URL: https://github.com/user/repo/releases/download/v1.0/file.zip
Mode: Smart mode (testing and selecting fastest method)

✓ TurboCdn initialized in smart mode (auto-selecting best method)

Testing download methods...
  Direct URL: 150ms latency
  CDN (ghfast.top): 80ms latency
  
Selected: CDN (ghfast.top) - 47% faster

🎉 Download completed successfully!
   📁 ./file.zip
   📊 25.50 MB (12.30 MB/s)

Performance Optimization

Test Timeout

Smart mode uses short timeouts for testing:

Test Type	Timeout
HEAD request	3 seconds
Initial bytes	5 seconds

Caching

Test results are cached to avoid repeated testing:

• Cache Duration: 5 minutes
• Cache Key: URL + region
• Invalidation: On network change

When to Override

Use --no-cdn when:

• You know the direct source is fastest
• CDN mirrors are known to be outdated
• Debugging download issues

Use --force-cdn when:

• Direct source is blocked or slow
• You want consistent CDN behavior
• Testing CDN performance

Troubleshooting

Smart Mode Chooses Wrong Method

If smart mode consistently picks the slower option:

1. Check verbose output: See actual latencies
2. Clear cache: Results may be stale
3. Report issue: May indicate a bug

# See detailed decision process
turbo-cdn dl "https://example.com/file.zip" --verbose

# Force specific mode for comparison
turbo-cdn dl "https://example.com/file.zip" --no-cdn --verbose
turbo-cdn dl "https://example.com/file.zip" --force-cdn --verbose

Slow Testing Phase

If the testing phase takes too long:

• Network may be unstable
• Consider using --force-cdn or --no-cdn directly

Next Steps

• Adaptive Concurrency - Dynamic parallelization
• Smart Chunking - Intelligent chunk sizing