Improve logic for handling bindings using custom hostnames.

Author: CZEMacLeod

src/C3D/Extensions/Aspire/IISExpress/IISEndPointConfigurator.cs

@@ -113,7 +113,7 @@ void SaveConfig()
             var matches = new Dictionary<EndpointAnnotation, Configuration.Binding>();
             foreach (var binding in siteConfig.Bindings.Binding)
             {
-                var endpoint = project.AddOrUpdateEndpointFromBinding(binding);
+                var endpoint = project.AddOrUpdateEndpointFromBinding(binding, logger);
                 matches[endpoint] = binding;
             }
 

src/C3D/Extensions/Aspire/IISExpress/IISExpressEntensions.cs

@@ -207,6 +207,19 @@ public static void MarkPortAsUsed(int port)
         ap[port] = true;
     }
 
+    public static bool TryMarkPortAsUsed(int port)
+    {
+        ArgumentOutOfRangeException.ThrowIfLessThan(port, 1, nameof(port));
+        ArgumentOutOfRangeException.ThrowIfGreaterThan(port, 65535, nameof(port));
+        var ap = AllocatedPorts;
+        if (ap[port])
+        {
+            return false; // Port is already allocated
+        }
+        ap[port] = true;
+        return true; // Successfully marked the port as used
+    }
+
     public static int GetRandomFreePort(int minPort, int maxPort)
     {
         var ap = AllocatedPorts;
@@ -322,13 +335,13 @@ internal static void ShowIISExpressHttpsEndpointInformation<T>(this T resource,
         });
     }
 
-    internal static EndpointAnnotation AddOrUpdateEndpointFromBinding(this IResourceWithEndpoints resource, Binding binding)
+    internal static EndpointAnnotation AddOrUpdateEndpointFromBinding(this IResourceWithEndpoints resource, Binding binding, ILogger? logger = null)
     {
         var hostName = string.IsNullOrEmpty(binding.HostName) ? "localhost" : binding.HostName;
 
         var endpoint = resource.Annotations
                             .OfType<EndpointAnnotation>()
-                            .Where(ea => StringComparer.OrdinalIgnoreCase.Equals(ea.Name, binding.Protocol) && 
+                            .Where(ea => StringComparer.OrdinalIgnoreCase.Equals(ea.Name, binding.Protocol) &&
                                          StringComparer.OrdinalIgnoreCase.Equals(ea.TargetHost, hostName))
                             .SingleOrDefault();
         if (endpoint is null)
@@ -341,15 +354,24 @@ internal static EndpointAnnotation AddOrUpdateEndpointFromBinding(this IResource
             endpoint = new EndpointAnnotation(System.Net.Sockets.ProtocolType.Tcp, name: $"{binding.Protocol}-{binding.Port}-{hostName}");
             resource.Annotations.Add(endpoint);
         }
-        if (StringComparer.OrdinalIgnoreCase.Equals(hostName,"localhost"))
+        if (StringComparer.OrdinalIgnoreCase.Equals(hostName, "localhost"))
         {
             MarkPortAsUsed(binding.Port);
         }
+        else
+        {
+            if (!TryMarkPortAsUsed(binding.Port))
+            {
+                logger?.LogWarning("Port {Port} is already allocated. Ensure each binding has a unique hostName.", binding.Port);
+            }
+            logger?.LogInformation("It is recommended to use 'localhost' with unique ports for IIS Express endpoints to avoid port conflicts.");
+            // If the hostName is not localhost, we disable the proxy support so that SNI and host name routing works as expected.
+            endpoint.IsProxied = false;
+        }
 
         endpoint.TargetPort = binding.Port;
         endpoint.TargetHost = hostName;
         endpoint.UriScheme = binding.Protocol;
-        //endpoint.IsProxied = false;
 
         return endpoint;
     }