feat(smart-proxy): add UDP transport support with QUIC/HTTP3 routing and datagram handler relay

rust/crates/rustproxy-http/src/connection_pool.rs

@@ -1,7 +1,7 @@
-//! Backend connection pool for HTTP/1.1 and HTTP/2.
+//! Backend connection pool for HTTP/1.1, HTTP/2, and HTTP/3 (QUIC).
 //!
 //! Reuses idle keep-alive connections to avoid per-request TCP+TLS handshakes.
-//! HTTP/2 connections are multiplexed (clone the sender for each request).
+//! HTTP/2 and HTTP/3 connections are multiplexed (clone the sender / share the connection).
 
 use std::sync::Arc;
 use std::sync::atomic::{AtomicU64, Ordering};
@@ -19,9 +19,17 @@ const IDLE_TIMEOUT: Duration = Duration::from_secs(90);
 /// Background eviction interval.
 const EVICTION_INTERVAL: Duration = Duration::from_secs(30);
 /// Maximum age for pooled HTTP/2 connections before proactive eviction.
-/// Prevents staleness from backends that close idle connections (e.g. nginx GOAWAY).
-/// 120s is well within typical server GOAWAY windows (nginx: ~60s idle, envoy: ~60s).
 const MAX_H2_AGE: Duration = Duration::from_secs(120);
+/// Maximum age for pooled QUIC/HTTP/3 connections.
+const MAX_H3_AGE: Duration = Duration::from_secs(120);
+
+/// Protocol for pool key discrimination.
+#[derive(Clone, Debug, Hash, Eq, PartialEq)]
+pub enum PoolProtocol {
+    H1,
+    H2,
+    H3,
+}
 
 /// Identifies a unique backend endpoint.
 #[derive(Clone, Debug, Hash, Eq, PartialEq)]
@@ -29,7 +37,7 @@ pub struct PoolKey {
     pub host: String,
     pub port: u16,
     pub use_tls: bool,
-    pub h2: bool,
+    pub protocol: PoolProtocol,
 }
 
 /// An idle HTTP/1.1 sender with a timestamp for eviction.
@@ -47,13 +55,22 @@ struct PooledH2 {
     generation: u64,
 }
 
+/// A pooled QUIC/HTTP/3 connection (multiplexed like H2).
+pub struct PooledH3 {
+    pub connection: quinn::Connection,
+    pub created_at: Instant,
+    pub generation: u64,
+}
+
 /// Backend connection pool.
 pub struct ConnectionPool {
     /// HTTP/1.1 idle connections indexed by backend key.
     h1_pool: Arc<DashMap<PoolKey, Vec<IdleH1>>>,
     /// HTTP/2 multiplexed connections indexed by backend key.
     h2_pool: Arc<DashMap<PoolKey, PooledH2>>,
-    /// Monotonic generation counter for H2 pool entries.
+    /// HTTP/3 (QUIC) connections indexed by backend key.
+    h3_pool: Arc<DashMap<PoolKey, PooledH3>>,
+    /// Monotonic generation counter for H2/H3 pool entries.
     h2_generation: AtomicU64,
     /// Handle for the background eviction task.
     eviction_handle: Option<tokio::task::JoinHandle<()>>,
@@ -64,16 +81,19 @@ impl ConnectionPool {
     pub fn new() -> Self {
         let h1_pool: Arc<DashMap<PoolKey, Vec<IdleH1>>> = Arc::new(DashMap::new());
         let h2_pool: Arc<DashMap<PoolKey, PooledH2>> = Arc::new(DashMap::new());
+        let h3_pool: Arc<DashMap<PoolKey, PooledH3>> = Arc::new(DashMap::new());
 
         let h1_clone = Arc::clone(&h1_pool);
         let h2_clone = Arc::clone(&h2_pool);
+        let h3_clone = Arc::clone(&h3_pool);
         let eviction_handle = tokio::spawn(async move {
-            Self::eviction_loop(h1_clone, h2_clone).await;
+            Self::eviction_loop(h1_clone, h2_clone, h3_clone).await;
         });
 
         Self {
             h1_pool,
             h2_pool,
+            h3_pool,
             h2_generation: AtomicU64::new(0),
             eviction_handle: Some(eviction_handle),
         }
@@ -173,10 +193,57 @@ impl ConnectionPool {
         gen
     }
 
+    // ── HTTP/3 (QUIC) pool methods ──
+
+    /// Try to get a pooled QUIC connection for the given key.
+    /// QUIC connections are multiplexed — the connection is shared, not removed.
+    pub fn checkout_h3(&self, key: &PoolKey) -> Option<(quinn::Connection, Duration)> {
+        let entry = self.h3_pool.get(key)?;
+        let pooled = entry.value();
+        let age = pooled.created_at.elapsed();
+
+        if age >= MAX_H3_AGE {
+            drop(entry);
+            self.h3_pool.remove(key);
+            return None;
+        }
+
+        // Check if QUIC connection is still alive
+        if pooled.connection.close_reason().is_some() {
+            drop(entry);
+            self.h3_pool.remove(key);
+            return None;
+        }
+
+        Some((pooled.connection.clone(), age))
+    }
+
+    /// Register a QUIC connection in the pool. Returns the generation ID.
+    pub fn register_h3(&self, key: PoolKey, connection: quinn::Connection) -> u64 {
+        let gen = self.h2_generation.fetch_add(1, Ordering::Relaxed);
+        self.h3_pool.insert(key, PooledH3 {
+            connection,
+            created_at: Instant::now(),
+            generation: gen,
+        });
+        gen
+    }
+
+    /// Remove a QUIC connection only if generation matches.
+    pub fn remove_h3_if_generation(&self, key: &PoolKey, expected_gen: u64) {
+        if let Some(entry) = self.h3_pool.get(key) {
+            if entry.value().generation == expected_gen {
+                drop(entry);
+                self.h3_pool.remove(key);
+            }
+        }
+    }
+
     /// Background eviction loop — runs every EVICTION_INTERVAL to remove stale connections.
     async fn eviction_loop(
         h1_pool: Arc<DashMap<PoolKey, Vec<IdleH1>>>,
         h2_pool: Arc<DashMap<PoolKey, PooledH2>>,
+        h3_pool: Arc<DashMap<PoolKey, PooledH3>>,
     ) {
         let mut interval = tokio::time::interval(EVICTION_INTERVAL);
         loop {
@@ -206,6 +273,19 @@ impl ConnectionPool {
             for key in dead_h2 {
                 h2_pool.remove(&key);
             }
+
+            // Evict dead or aged-out H3 (QUIC) connections
+            let mut dead_h3 = Vec::new();
+            for entry in h3_pool.iter() {
+                if entry.value().connection.close_reason().is_some()
+                    || entry.value().created_at.elapsed() >= MAX_H3_AGE
+                {
+                    dead_h3.push(entry.key().clone());
+                }
+            }
+            for key in dead_h3 {
+                h3_pool.remove(&key);
+            }
         }
     }
 }