Possible fix for port exhaustion during integration tests

src/Dapr.Testcontainers/Common/PortUtilities.cs

@@ -11,25 +11,63 @@
 // limitations under the License.
 //  ------------------------------------------------------------------------
 
+using System;
 using System.Net;
 using System.Net.Sockets;
 
 namespace Dapr.Testcontainers.Common;
 
+/// <summary>
+/// Represents a temporary reservation for a TCP port.
+/// </summary>
+public sealed class PortReservation : IDisposable
+{
+    private Socket? _socket;
+
+    internal PortReservation(Socket socket)
+    {
+        _socket = socket;
+        Port = ((IPEndPoint)socket.LocalEndPoint!).Port;
+    }
+
+    /// <summary>
+    /// The reserved port number.
+    /// </summary>
+    public int Port { get; }
+
+    /// <inheritdoc />
+    public void Dispose()
+    {
+        _socket?.Dispose();
+        _socket = null;
+    }
+}
+
 /// <summary>
 /// Provides port-related utilities.
 /// </summary>
 public static class PortUtilities
 {
+    /// <summary>
+    /// Reserves an available TCP port until the returned reservation is disposed.
+    /// </summary>
+    /// <returns>A <see cref="PortReservation"/> representing the reserved port.</returns>
+    public static PortReservation ReserveTcpPort()
+    {
+        var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.ExclusiveAddressUse, true);
+        socket.Bind(new IPEndPoint(IPAddress.Any, 0));
+        return new PortReservation(socket);
+    }
+
     /// <summary>
     /// Gets an available TCP port from the OS. This is a best-effort snapshot
     /// and does not reserve the port for later use.
     /// </summary>
     /// <returns>The available port number.</returns>
     public static int GetAvailablePort()
     {
-        using var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
-        socket.Bind(new IPEndPoint(IPAddress.Any, 0));
-        return ((IPEndPoint)socket.LocalEndPoint!).Port;
+        using var reservation = ReserveTcpPort();
+        return reservation.Port;
     }
 }

src/Dapr.Testcontainers/Common/Testing/DaprTestApplicationBuilder.cs

@@ -123,14 +123,25 @@ public async Task<DaprTestApplication> BuildAndStartAsync()
         for (var attempt = 1; attempt <= maxAttempts; attempt++)
         {
             WebApplication? attemptApp = null;
+            PortReservation? httpReservation = null;
+            PortReservation? grpcReservation = null;
 
             try
             {
-                // Pre-assign prots for the app knows where Dapr will be (avoid collisions)
-                var httpPort = PortUtilities.GetAvailablePort();
-                var grpcPort = PortUtilities.GetAvailablePort();
-                while (grpcPort == httpPort)
-                    grpcPort = PortUtilities.GetAvailablePort();
+                // Pre-assign ports so the app knows where Dapr will be (avoid collisions)
+                httpReservation = PortUtilities.ReserveTcpPort();
+                do
+                {
+                    grpcReservation = PortUtilities.ReserveTcpPort();
+                    if (grpcReservation.Port == httpReservation.Port)
+                    {
+                        grpcReservation.Dispose();
+                        grpcReservation = null;
+                    }
+                } while (grpcReservation is null);
+
+                var httpPort = httpReservation.Port;
+                var grpcPort = grpcReservation.Port;
 
                 harness.SetPorts(httpPort, grpcPort);
 
@@ -142,6 +153,12 @@ public async Task<DaprTestApplication> BuildAndStartAsync()
                     harness.SetAppPort(GetBoundPort(attemptApp));
                 }
 
+                // Release port reservations just before daprd starts to minimize collisions.
+                httpReservation.Dispose();
+                grpcReservation.Dispose();
+                httpReservation = null;
+                grpcReservation = null;
+
                 await harness.InitializeAsync();
 
                 return new DaprTestApplication(harness, attemptApp);
@@ -162,7 +179,12 @@ public async Task<DaprTestApplication> BuildAndStartAsync()
                     }
                 }
 
-                // Try again with a frest set of ports
+                // Try again with a fresh set of ports
+            }
+            finally
+            {
+                httpReservation?.Dispose();
+                grpcReservation?.Dispose();
             }
         }