Add support for externally supplied worker extensions project

samples/FunctionApp/FunctionApp.csproj

@@ -9,7 +9,7 @@
 
   <ItemGroup>
     <PackageReference Include="Microsoft.ApplicationInsights.WorkerService" Version="2.22.0" />
-    <PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="1.18.1" />
+    <PackageReference Include="Microsoft.Azure.Functions.Worker.Sdk" Version="$(SdkVersion)" />
     <PackageReference Include="Newtonsoft.Json" Version="13.0.3" />
     <PackageReference Include="System.Net.NameResolution" Version="4.3.0" />
     <PackageReference Include="Microsoft.Azure.Functions.Worker.Extensions.Abstractions" Version="1.3.0" />

sdk/Sdk/ExtensionsCsprojGenerator.cs

@@ -10,8 +10,6 @@ namespace Microsoft.Azure.Functions.Worker.Sdk
 {
     internal class ExtensionsCsprojGenerator
     {
-        internal const string ExtensionsProjectName = "WorkerExtensions.csproj";
-
         private readonly IDictionary<string, string> _extensions;
         private readonly string _outputPath;
         private readonly string _targetFrameworkIdentifier;
@@ -29,22 +27,20 @@ public ExtensionsCsprojGenerator(IDictionary<string, string> extensions, string
 
         public void Generate()
         {
-            var extensionsCsprojFilePath = Path.Combine(_outputPath, ExtensionsProjectName);
-
             string csproj = GetCsProjContent();
-            if (File.Exists(extensionsCsprojFilePath))
+            if (File.Exists(_outputPath))
             {
-                string existing = File.ReadAllText(extensionsCsprojFilePath);
+                string existing = File.ReadAllText(_outputPath);
                 if (string.Equals(csproj, existing, StringComparison.Ordinal))
                 {
                     // If contents are the same, only touch the file to update timestamp.
-                    File.SetLastWriteTimeUtc(extensionsCsprojFilePath, DateTime.UtcNow);
+                    File.SetLastWriteTimeUtc(_outputPath, DateTime.UtcNow);
                     return;
                 }
             }
 
-            RecreateDirectory(_outputPath);
-            File.WriteAllText(extensionsCsprojFilePath, csproj);
+            RecreateDirectory(Path.GetDirectoryName(_outputPath));
+            File.WriteAllText(_outputPath, csproj);
         }
 
         private void RecreateDirectory(string directoryPath)

sdk/Sdk/ExtensionsMetadata.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
 using System.Collections.Generic;
@@ -9,6 +9,6 @@ namespace Microsoft.Azure.Functions.Worker.Sdk
     public class ExtensionsMetadata
     {
         [JsonPropertyName("extensions")]
-        public IEnumerable<ExtensionReference>? Extensions { get; set; }
+        public List<ExtensionReference> Extensions { get; set; } = new List<ExtensionReference>();
     }
 }

sdk/Sdk/ExtensionsMetadataEnhancer.cs

@@ -2,7 +2,11 @@
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
 using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Reflection;
 using System.Text.RegularExpressions;
+using Mono.Cecil;
 
 namespace Microsoft.Azure.Functions.Worker.Sdk
 {
@@ -25,6 +29,34 @@ public static void AddHintPath(IEnumerable<ExtensionReference> extensions)
             }
         }
 
+        public static IEnumerable<ExtensionReference> GetWebJobsExtensions(string fileName)
+        {
+            // NOTE: this is an incomplete approach to getting extensions and is intended only for our usages.
+            // Running this with arbitrary assemblies (especially user supplied) can lead to exceptions.
+            AssemblyDefinition assembly = AssemblyDefinition.ReadAssembly(fileName);
+            IEnumerable<CustomAttribute> attributes = assembly.Modules.SelectMany(p => p.GetCustomAttributes())
+                .Where(a => a.AttributeType.FullName == "Microsoft.Azure.WebJobs.Hosting.WebJobsStartupAttribute");
+
+            foreach (CustomAttribute attribute in attributes)
+            {
+                CustomAttributeArgument typeProperty = attribute.ConstructorArguments.ElementAtOrDefault(0);
+                CustomAttributeArgument nameProperty = attribute.ConstructorArguments.ElementAtOrDefault(1);
+
+                TypeDefinition typeDef = (TypeDefinition)typeProperty.Value;
+                string assemblyQualifiedName = Assembly.CreateQualifiedName(
+                    typeDef.Module.Assembly.FullName, GetReflectionFullName(typeDef));
+
+                string name = GetName((string)nameProperty.Value, typeDef);
+
+                yield return new ExtensionReference
+                {
+                    Name = name,
+                    TypeName = assemblyQualifiedName,
+                    HintPath = $@"{ExtensionsBinaryDirectoryPath}/{Path.GetFileName(fileName)}",
+                };
+            }
+        }
+
         private static string? GetAssemblyNameOrNull(string? typeName)
         {
             if (typeName == null)
@@ -41,5 +73,33 @@ public static void AddHintPath(IEnumerable<ExtensionReference> extensions)
 
             return null;
         }
+
+        // Copying the WebJobsStartup constructor logic from:
+        // https://github.com/Azure/azure-webjobs-sdk/blob/e5417775bcb8c8d3d53698932ca8e4e265eac66d/src/Microsoft.Azure.WebJobs.Host/Hosting/WebJobsStartupAttribute.cs#L33-L47.
+        private static string GetName(string name, TypeDefinition startupTypeDef)
+        {
+            if (string.IsNullOrEmpty(name))
+            {
+                // for a startup class named 'CustomConfigWebJobsStartup' or 'CustomConfigStartup',
+                // default to a name 'CustomConfig'
+                name = startupTypeDef.Name;
+                int idx = name.IndexOf("WebJobsStartup");
+                if (idx < 0)
+                {
+                    idx = name.IndexOf("Startup");
+                }
+                if (idx > 0)
+                {
+                    name = name.Substring(0, idx);
+                }
+            }
+
+            return name;
+        }
+
+        private static string GetReflectionFullName(TypeReference typeRef)
+        {
+            return typeRef.FullName.Replace("/", "+");
+        }
     }
 }