test: verify native connection capacity recovery

transport/native/server_test.go

@@ -444,6 +444,74 @@ func TestServerConcurrentRequestLimit(t *testing.T) {
 	}
 }
 
+func TestServerConnectionLimitReleasesAfterRequest(t *testing.T) {
+	started := make(chan struct{})
+	release := make(chan struct{})
+	application := omni.NewWithRouter(netrouter.New())
+	application.GET("/hold", func(ctx *omni.Context) error {
+		close(started)
+		<-release
+		return ctx.OK("done")
+	})
+	application.GET("/health", func(ctx *omni.Context) error { return ctx.OK("ok") })
+	server := native.New(application)
+	server.MaxConnections = 1
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	done := make(chan error, 1)
+	go func() { done <- server.Serve(context.Background(), listener) }()
+	waitForServer(t, listener.Addr().String())
+	defer stopServer(t, server, listener, done)
+
+	first, err := net.Dial("tcp", listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer first.Close()
+	_, _ = io.WriteString(first, "GET /hold HTTP/1.1\r\nHost: test\r\nConnection: close\r\n\r\n")
+	select {
+	case <-started:
+	case <-time.After(time.Second):
+		t.Fatal("first request did not start")
+	}
+
+	second, err := net.Dial("tcp", listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	second.SetReadDeadline(time.Now().Add(time.Second))
+	_, _ = io.WriteString(second, "GET /health HTTP/1.1\r\nHost: test\r\nConnection: close\r\n\r\n")
+	if _, err := second.Read(make([]byte, 1)); err == nil {
+		second.Close()
+		t.Fatal("connection over MaxConnections was not rejected")
+	}
+	second.Close()
+
+	close(release)
+	firstResponse, err := http.ReadResponse(bufio.NewReader(first), &http.Request{Method: http.MethodGet})
+	if err != nil {
+		t.Fatal(err)
+	}
+	firstResponse.Body.Close()
+
+	third, err := net.Dial("tcp", listener.Addr().String())
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer third.Close()
+	_, _ = io.WriteString(third, "GET /health HTTP/1.1\r\nHost: test\r\nConnection: close\r\n\r\n")
+	thirdResponse, err := http.ReadResponse(bufio.NewReader(third), &http.Request{Method: http.MethodGet})
+	if err != nil {
+		t.Fatal(err)
+	}
+	thirdResponse.Body.Close()
+	if thirdResponse.StatusCode != http.StatusOK {
+		t.Fatalf("connection slot was not released, got status %d", thirdResponse.StatusCode)
+	}
+}
+
 func TestServerReadHeaderTimeout(t *testing.T) {
 	application := omni.NewWithRouter(netrouter.New())
 	application.GET("/health", func(ctx *omni.Context) error { return ctx.OK("ok") })