Unify GetLaunchSettings implementations between Aspire.Hosting and Aspire.Hosting.Testing

src/Aspire.Hosting.Testing/Aspire.Hosting.Testing.csproj

@@ -12,6 +12,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Compile Include="$(SharedDir)LaunchProfiles\LaunchSettingsReader.cs" Link="LaunchSettingsReader.cs" />
     <Compile Include="$(SharedDir)LaunchProfiles\LaunchSettingsSerializerContext.cs" Link="LaunchSettingsSerializerContext.cs" />
     <Compile Include="$(SharedDir)\KnownConfigNames.cs" Link="KnownConfigNames.cs" />
   </ItemGroup>

src/Aspire.Hosting.Testing/DistributedApplicationFactory.cs

@@ -3,7 +3,6 @@
 
 using System.Diagnostics;
 using System.Reflection;
-using System.Text.Json;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
@@ -342,30 +341,7 @@ void SetDefault(string key, string? value)
             return null;
         }
 
-        var projectFileInfo = new DirectoryInfo(appHostPath);
-        var launchSettingsFilePath = projectFileInfo.FullName switch
-        {
-            null => Path.Combine("Properties", "launchSettings.json"),
-            _ => Path.Combine(projectFileInfo.FullName, "Properties", "launchSettings.json")
-        };
-
-        // It isn't mandatory that the launchSettings.json file exists!
-        if (!File.Exists(launchSettingsFilePath))
-        {
-            return null;
-        }
-
-        using var stream = File.OpenRead(launchSettingsFilePath);
-        try
-        {
-            var settings = JsonSerializer.Deserialize(stream, LaunchSettingsSerializerContext.Default.LaunchSettings);
-            return settings;
-        }
-        catch (JsonException ex)
-        {
-            var message = $"Failed to get effective launch profile for project '{appHostPath}'. There is malformed JSON in the project's launch settings file at '{launchSettingsFilePath}'.";
-            throw new DistributedApplicationException(message, ex);
-        }
+        return LaunchSettingsReader.GetLaunchSettingsFromDirectory(appHostPath, $"project '{appHostPath}'");
     }
 
     private void OnBuilderCreatedCore(DistributedApplicationBuilder applicationBuilder)

src/Shared/LaunchProfiles/LaunchProfileExtensions.cs

@@ -3,7 +3,6 @@
 
 using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
-using System.Text.Json;
 using Aspire.Hosting.ApplicationModel;
 using Aspire.Hosting.Resources;
 
@@ -109,19 +108,7 @@ internal static class LaunchProfileExtensions
             }
         }
 
-        using var stream = File.OpenRead(launchSettingsFilePath);
-
-        try
-        {
-            var settings = JsonSerializer.Deserialize(stream, LaunchSettingsSerializerContext.Default.LaunchSettings);
-            return settings;
-        }
-        catch (JsonException ex)
-        {
-            var message = $"Failed to get effective launch profile for project resource '{resourceName}'. There is malformed JSON in the project's launch settings file at '{launchSettingsFilePath}'.";
-            throw new DistributedApplicationException(message, ex);
-        }
-
+        return LaunchSettingsReader.ReadLaunchSettingsFile(launchSettingsFilePath, $"project resource '{resourceName}'");
     }
 
     private static readonly LaunchProfileSelector[] s_launchProfileSelectors =

src/Shared/LaunchProfiles/LaunchSettingsReader.cs

@@ -0,0 +1,51 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Text.Json;
+
+namespace Aspire.Hosting;
+
+internal static class LaunchSettingsReader
+{
+    /// <summary>
+    /// Reads launch settings from the <c>Properties/launchSettings.json</c> file within the specified directory.
+    /// </summary>
+    /// <param name="directoryPath">The directory to look for launch settings in. If <see langword="null"/>, a relative path is used.</param>
+    /// <param name="resourceIdentifier">A descriptive identifier used in error messages when JSON parsing fails.</param>
+    /// <returns>The deserialized <see cref="LaunchSettings"/>, or <see langword="null"/> if the file does not exist.</returns>
+    internal static LaunchSettings? GetLaunchSettingsFromDirectory(string? directoryPath, string resourceIdentifier)
+    {
+        var launchSettingsFilePath = directoryPath is null
+            ? Path.Combine("Properties", "launchSettings.json")
+            : Path.Combine(Path.GetFullPath(directoryPath), "Properties", "launchSettings.json");
+
+        if (!File.Exists(launchSettingsFilePath))
+        {
+            return null;
+        }
+
+        return ReadLaunchSettingsFile(launchSettingsFilePath, resourceIdentifier);
+    }
+
+    /// <summary>
+    /// Reads and deserializes launch settings from the specified file.
+    /// </summary>
+    /// <param name="launchSettingsFilePath">The path to the launch settings file.</param>
+    /// <param name="resourceIdentifier">A descriptive identifier used in error messages when JSON parsing fails.</param>
+    /// <returns>The deserialized <see cref="LaunchSettings"/>.</returns>
+    /// <exception cref="DistributedApplicationException">Thrown when the file is empty or contains malformed JSON.</exception>
+    internal static LaunchSettings? ReadLaunchSettingsFile(string launchSettingsFilePath, string resourceIdentifier)
+    {
+        using var stream = File.OpenRead(launchSettingsFilePath);
+
+        try
+        {
+            return JsonSerializer.Deserialize(stream, LaunchSettingsSerializerContext.Default.LaunchSettings);
+        }
+        catch (JsonException ex)
+        {
+            var message = $"Failed to get effective launch profile for {resourceIdentifier}. There is malformed JSON in the project's launch settings file at '{launchSettingsFilePath}'.";
+            throw new DistributedApplicationException(message, ex);
+        }
+    }
+}