Bits of .NET

📋 Headers Contain Metadata

Server sends headers with response. Read response headers for content type, cache, rate limits, authentication.

📝 Reading Headers

fetch('/api/data')
  .then(response => {
    // Read specific header
    const contentType = response.headers.get('Content-Type');
    const cacheControl = response.headers.get('Cache-Control');
    const rateLimit = response.headers.get('X-RateLimit-Remaining');
    
    console.log('Content-Type:', contentType);
    console.log('Rate limit remaining:', rateLimit);
    
    // Check if header exists
    if (response.headers.has('X-Custom-Header')) {
      console.log('Custom header present');
    }
    
    // Iterate all headers
    for (let [key, value] of response.headers) {
      console.log(`${key}: ${value}`);
    }
    
    return response.json();
  });

🎯 Useful Headers

// Content
Content-Type: application/json
Content-Length: 1024
Content-Encoding: gzip

// Caching
Cache-Control: max-age=3600
ETag: "abc123"
Last-Modified: Mon, 15 Jan 2024 12:00:00 GMT

// Rate limiting
X-RateLimit-Limit: 100
X-RateLimit-Remaining: 95
X-RateLimit-Reset: 1705334400

// Authentication
WWW-Authenticate: Bearer
Set-Cookie: session=abc123

// CORS
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET, POST, PUT, DELETE

💡 Use Cases

• Check rate limits (avoid hitting limits)
• Verify content type (JSON, HTML, etc.)
• Cache management (ETag, Cache-Control)
• Authentication (Set-Cookie, WWW-Authenticate)
• Debugging (server headers)