Diagnose hostname issue on macOS

.github/workflows/TestHostName.yml

@@ -0,0 +1,50 @@
+name: TestHostName
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+    - main
+    - '[0-9]+.x'
+  pull_request:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+  pull-requests: write
+
+env:
+  DOTNET_CLI_TELEMETRY_OPTOUT: 1
+  DOTNET_NOLOGO: true
+
+jobs:
+  testHostName:
+    name: Test hostname on ${{ matrix.os }}
+    timeout-minutes: 15
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
+        include:
+        - os: ubuntu-latest
+        - os: windows-latest
+        - os: macos-latest
+    runs-on: ${{ matrix.os }}
+    continue-on-error: true
+
+    steps:
+    - name: resolve1
+      if: always()
+      shell: pwsh
+      run: |
+        $hostName = [System.Net.Dns]::GetHostName()
+        [System.Net.Dns]::GetHostEntry($hostName)
+    - name: resolve2
+      if: always()
+      shell: pwsh
+      run: |
+        $hostName = [System.Net.Dns]::GetHostName()
+        [System.Net.Dns]::GetHostEntry($hostName + ".local")

src/Common/src/Common/Net/DomainNameResolver.cs

@@ -42,28 +42,49 @@ private DomainNameResolver()
 
     public string? ResolveHostName(bool throwOnError = false)
     {
+        string? resultingHostName = null;
+        string? resultingHostEntryHostName = null;
+        bool? workaroundApplied = null;
+
         try
         {
             string hostName = Dns.GetHostName();
+            resultingHostName = hostName;
 
             if (string.IsNullOrEmpty(hostName))
             {
                 // Workaround for failure when running on macOS.
                 // See https://github.com/actions/runner-images/issues/1335 and https://github.com/dotnet/runtime/issues/36849.
+
                 hostName = "localhost";
+                workaroundApplied = true;
             }
 
             IPHostEntry hostEntry = Dns.GetHostEntry(hostName);
-            return hostEntry.HostName;
+            resultingHostEntryHostName = hostEntry.HostName;
+
+            if (string.IsNullOrEmpty(resultingHostEntryHostName))
+            {
+                throw new InvalidOperationException($"IPHostEntry.HostName is {GetTextFor(resultingHostEntryHostName)}.");
+            }
+
+            return resultingHostEntryHostName;
         }
-        catch (Exception)
+        catch (Exception exception)
         {
             if (throwOnError)
             {
-                throw;
+                throw new InvalidOperationException(
+                    $"Failed to resolve hostname. First={GetTextFor(resultingHostName)}, Second={GetTextFor(resultingHostEntryHostName)}, WorkaroundApplied={workaroundApplied}",
+                    exception);
             }
 
             return null;
         }
     }
+
+    private static string GetTextFor(string? value)
+    {
+        return value == null ? "null" : "empty";
+    }
 }

src/Discovery/src/Consul/PostConfigureConsulDiscoveryOptions.cs

@@ -43,7 +43,7 @@ public void PostConfigure(string? name, ConsulDiscoveryOptions options)
         options.ServiceName = GetServiceName(options);
 
         HostInfo? hostInfo = options.UseNetworkInterfaces ? _inetUtils.FindFirstNonLoopbackHostInfo() : null;
-        options.HostName ??= hostInfo != null ? hostInfo.Hostname : _domainNameResolver.ResolveHostName();
+        options.HostName ??= hostInfo != null ? hostInfo.Hostname : _domainNameResolver.ResolveHostName(true);
 
         if (string.IsNullOrWhiteSpace(options.IPAddress))
         {

src/Discovery/src/Consul/Registry/ConsulRegistration.cs

@@ -35,7 +35,7 @@ internal sealed class ConsulRegistration : IServiceInstance
     public bool IsSecure => _optionsMonitor.CurrentValue.EffectiveScheme == "https";
 
     /// <inheritdoc />
-    public Uri Uri => new($"{_optionsMonitor.CurrentValue.EffectiveScheme}://{Host}:{Port}");
+    public Uri Uri => FormatUri();
 
     /// <inheritdoc />
     public Uri? NonSecureUri => IsSecure ? null : Uri;
@@ -73,6 +73,20 @@ internal ConsulRegistration(AgentServiceRegistration innerRegistration, IOptions
         Metadata = innerRegistration.Meta.AsReadOnly();
     }
 
+    private Uri FormatUri()
+    {
+        string scheme = _optionsMonitor.CurrentValue.EffectiveScheme;
+
+        try
+        {
+            return new Uri($"{scheme}://{Host}:{Port}");
+        }
+        catch (UriFormatException exception)
+        {
+            throw new UriFormatException($"Failed to build URI from components. Scheme={scheme}, Host={Host},Port={Port}.", exception);
+        }
+    }
+
     /// <summary>
     /// Creates a registration for the currently running app, to be submitted to the Consul server.
     /// </summary>