Implement rate limiting with 41 responses and comprehensive logging

- Add concurrent connection handling with tokio::spawn for proper rate limiting
- Send '41 Server unavailable' responses instead of dropping connections
- Move request logger initialization earlier to enable rate limiting logs
- Add logging for rate limited requests: 'Concurrent request limit exceeded'
- Fix clippy warnings: needless borrows and match simplification
- Update test script analysis to expect 41 responses for rate limiting

src/main.rs

@@ -53,6 +53,11 @@ struct Args {
     /// Hostname for the server
     #[arg(short = 'H', long)]
     host: Option<String>,
+
+    /// TESTING ONLY: Add delay before processing (seconds) [debug builds only]
+    #[cfg(debug_assertions)]
+    #[arg(long, value_name = "SECONDS")]
+    test_processing_delay: Option<u64>,
 }
 
 
@@ -91,6 +96,16 @@ async fn main() {
         std::process::exit(1);
     }
 
+    // TESTING ONLY: Read delay argument (debug builds only)
+    #[cfg(debug_assertions)]
+    let test_processing_delay = args.test_processing_delay
+        .filter(|&d| d > 0 && d <= 300)
+        .unwrap_or(0);
+
+    // Production: always 0 delay
+    #[cfg(not(debug_assertions))]
+    let test_processing_delay = 0;
+
     // Validate directory
     let dir_path = Path::new(&root);
     if !dir_path.exists() || !dir_path.is_dir() {
@@ -120,10 +135,13 @@ async fn main() {
         let dir = root.clone();
         let expected_host = "localhost".to_string(); // Override for testing
         let max_concurrent = max_concurrent_requests;
-        if let Ok(stream) = acceptor.accept(stream).await {
-            if let Err(e) = server::handle_connection(stream, &dir, &expected_host, max_concurrent).await {
-                tracing::error!("Error handling connection: {}", e);
+        let test_delay = test_processing_delay;
+        tokio::spawn(async move {
+            if let Ok(stream) = acceptor.accept(stream).await {
+                if let Err(e) = server::handle_connection(stream, &dir, &expected_host, max_concurrent, test_delay).await {
+                    tracing::error!("Error handling connection: {}", e);
+                }
             }
-        }
+        });
     }
 }