Enhance TLS Emulator with ALPN Support and Add Adversarial Tests

- Modified `build_emulated_server_hello` to accept ALPN (Application-Layer Protocol Negotiation) as an optional parameter, allowing for the embedding of ALPN markers in the application data payload.
- Implemented logic to handle oversized ALPN values and ensure they do not interfere with the application data payload.
- Added new security tests in `emulator_security_tests.rs` to validate the behavior of the ALPN embedding, including scenarios for oversized ALPN and preference for certificate payloads over ALPN markers.
- Introduced `send_adversarial_tests.rs` to cover edge cases and potential issues in the middle proxy's send functionality, ensuring robustness against various failure modes.
- Updated `middle_proxy` module to include new test modules and ensure proper handling of writer commands during data transmission.

src/proxy/client.rs

@@ -31,19 +31,16 @@ struct UserConnectionReservation {
     user: String,
     ip: IpAddr,
     active: bool,
-    runtime_handle: Option<tokio::runtime::Handle>,
 }
 
 impl UserConnectionReservation {
     fn new(stats: Arc<Stats>, ip_tracker: Arc<UserIpTracker>, user: String, ip: IpAddr) -> Self {
-        let runtime_handle = tokio::runtime::Handle::try_current().ok();
         Self {
             stats,
             ip_tracker,
             user,
             ip,
             active: true,
-            runtime_handle,
         }
     }
 
@@ -64,29 +61,7 @@ impl Drop for UserConnectionReservation {
         }
         self.active = false;
         self.stats.decrement_user_curr_connects(&self.user);
-
-        if let Some(handle) = &self.runtime_handle {
-            let ip_tracker = self.ip_tracker.clone();
-            let user = self.user.clone();
-            let ip = self.ip;
-            let handle = handle.clone();
-            handle.spawn(async move {
-                ip_tracker.remove_ip(&user, ip).await;
-            });
-        } else if let Ok(handle) = tokio::runtime::Handle::try_current() {
-            let ip_tracker = self.ip_tracker.clone();
-            let user = self.user.clone();
-            let ip = self.ip;
-            handle.spawn(async move {
-                ip_tracker.remove_ip(&user, ip).await;
-            });
-        } else {
-            warn!(
-                user = %self.user,
-                ip = %self.ip,
-                "UserConnectionReservation dropped without Tokio runtime; IP reservation cleanup skipped"
-            );
-        }
+        self.ip_tracker.enqueue_cleanup(self.user.clone(), self.ip);
     }
 }