feat: add trusted proxy identity and overload stats

transport/native/server.go

@@ -53,27 +53,32 @@ type Server struct {
 	// when the listener and TLS configuration are assembled by the caller.
 	TLSConfig *tls.Config
 
-	mu             sync.Mutex
-	handler        http.Handler
-	listener       net.Listener
-	conns          map[*connection]struct{}
-	closing        bool
-	cancel         context.CancelFunc
-	wg             sync.WaitGroup
-	connSlots      chan struct{}
-	requestSlots   chan struct{}
-	accepted       atomic.Uint64
-	activeConns    atomic.Int64
-	activeRequests atomic.Int64
-	readerPool     sync.Pool
-	writerPool     sync.Pool
-	connectionPool sync.Pool
+	mu               sync.Mutex
+	handler          http.Handler
+	listener         net.Listener
+	conns            map[*connection]struct{}
+	closing          bool
+	cancel           context.CancelFunc
+	wg               sync.WaitGroup
+	connSlots        chan struct{}
+	requestSlots     chan struct{}
+	accepted         atomic.Uint64
+	rejectedConns    atomic.Uint64
+	rejectedRequests atomic.Uint64
+	activeConns      atomic.Int64
+	activeRequests   atomic.Int64
+	readerPool       sync.Pool
+	writerPool       sync.Pool
+	connectionPool   sync.Pool
 }
 
 // Stats is a point-in-time view of the native server lifecycle. Counters are
 // monotonic unless their name starts with Active.
 type Stats struct {
 	AcceptedConnections uint64 `json:"acceptedConnections"`
+	// Rejections count admission decisions, even if writing a 503 fails.
+	RejectedConnections uint64 `json:"rejectedConnections"`
+	RejectedRequests    uint64 `json:"rejectedRequests"`
 	ActiveConnections   int64  `json:"activeConnections"`
 	ActiveRequests      int64  `json:"activeRequests"`
 }
@@ -86,6 +91,8 @@ func (s *Server) Stats() Stats {
 	}
 	return Stats{
 		AcceptedConnections: s.accepted.Load(),
+		RejectedConnections: s.rejectedConns.Load(),
+		RejectedRequests:    s.rejectedRequests.Load(),
 		ActiveConnections:   s.activeConns.Load(),
 		ActiveRequests:      s.activeRequests.Load(),
 	}
@@ -252,6 +259,7 @@ func (s *Server) Serve(ctx context.Context, listener net.Listener) error {
 			select {
 			case slots <- struct{}{}:
 			default:
+				s.rejectedConns.Add(1)
 				_ = conn.Close()
 				continue
 			}
@@ -424,6 +432,7 @@ func (s *Server) serveConnection(baseCtx context.Context, state *connection) {
 				s.activeRequests.Add(-1)
 				return
 			default:
+				s.rejectedRequests.Add(1)
 				writer.Header().Set("Content-Type", "text/plain; charset=utf-8")
 				writer.WriteHeader(http.StatusServiceUnavailable)
 				writer.body.WriteString("server busy\n")

transport/native/server_test.go

@@ -711,6 +711,9 @@ func TestServerConcurrentRequestLimit(t *testing.T) {
 	if response.StatusCode != http.StatusServiceUnavailable {
 		t.Fatalf("expected 503 at concurrency limit, got %d", response.StatusCode)
 	}
+	if stats := server.Stats(); stats.RejectedRequests != 1 {
+		t.Fatalf("expected one rejected request, got %+v", stats)
+	}
 	close(release)
 	response, err = http.ReadResponse(bufio.NewReader(first), &http.Request{Method: http.MethodGet})
 	if err != nil {
@@ -842,6 +845,9 @@ func TestServerConnectionLimitReleasesAfterRequest(t *testing.T) {
 		t.Fatal("connection over MaxConnections was not rejected")
 	}
 	second.Close()
+	if stats := server.Stats(); stats.RejectedConnections < 1 {
+		t.Fatalf("expected rejected connection counter, got %+v", stats)
+	}
 
 	close(release)
 	firstResponse, err := http.ReadResponse(bufio.NewReader(first), &http.Request{Method: http.MethodGet})