update AddAWSLambdaBeforeSnapshotRequest() to support AOT by optimizing json serialization, adjust #if blocks and fix simple warnings

Author: ppittle

Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/Internal/LambdaRuntimeSupportServer.cs

@@ -16,7 +16,10 @@ namespace Amazon.Lambda.AspNetCoreServer.Hosting.Internal
     public abstract class LambdaRuntimeSupportServer : LambdaServer
     {
         private readonly IServiceProvider _serviceProvider;
+
+        #if NET8_0_OR_GREATER
         private readonly LambdaSnapstartExecuteRequestsBeforeSnapshotHelper _snapstartInitHelper;
+        #endif
 
         internal ILambdaSerializer Serializer;
 
@@ -27,7 +30,11 @@ public abstract class LambdaRuntimeSupportServer : LambdaServer
         public LambdaRuntimeSupportServer(IServiceProvider serviceProvider)
         {
             _serviceProvider = serviceProvider;
+
+            #if NET8_0_OR_GREATER
             _snapstartInitHelper = _serviceProvider.GetRequiredService<LambdaSnapstartExecuteRequestsBeforeSnapshotHelper>();
+            #endif
+
             Serializer = serviceProvider.GetRequiredService<ILambdaSerializer>();
         }
 
@@ -38,7 +45,6 @@ public LambdaRuntimeSupportServer(IServiceProvider serviceProvider)
         /// <param name="application"></param>
         /// <param name="cancellationToken"></param>
         /// <returns></returns>
-        [RequiresUnreferencedCode("_snapstartInitHelper Serializes objects to Json")]
         public override Task StartAsync<TContext>(IHttpApplication<TContext> application, CancellationToken cancellationToken)
         {
             base.StartAsync(application, cancellationToken);

Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/Internal/LambdaSnapstartExecuteRequestsBeforeSnapshotHelper.cs

@@ -5,6 +5,7 @@
 using System.Net;
 using System.Text;
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using Amazon.Lambda.APIGatewayEvents;
 using Amazon.Lambda.ApplicationLoadBalancerEvents;
 using Amazon.Lambda.RuntimeSupport;
@@ -14,6 +15,8 @@
 
 namespace Amazon.Lambda.AspNetCoreServer.Hosting.Internal;
 
+#if NET8_0_OR_GREATER
+
 /// <summary>
 /// Contains the plumbing to register a user provided <see cref="Func{HttpClient, Task}"/> inside
 /// <see cref="Amazon.Lambda.Core.SnapshotRestore.RegisterBeforeSnapshot"/>.
@@ -22,7 +25,7 @@ namespace Amazon.Lambda.AspNetCoreServer.Hosting.Internal;
 /// performance gains offered by SnapStart.
 /// <para />
 /// It works by construction a specialized <see cref="HttpClient" /> that will intercept requests
-/// and saved them inside <see cref="LambdaSnapstartInitializerHttpMessageHandler.CapturedHttpRequests" />.
+/// and saved them inside <see cref="LambdaSnapstartInitializerHttpMessageHandler.CapturedHttpRequestsJson" />.
 /// <para /> 
 /// Intercepted requests are then be processed later by <see cref="SnapstartHelperLambdaRequests.ExecuteSnapstartInitRequests"/>
 /// which will route them correctly through a simulated asp.net/lambda pipeline.
@@ -37,11 +40,8 @@ public LambdaSnapstartExecuteRequestsBeforeSnapshotHelper(LambdaEventSource lamb
     }
 
     /// <inheritdoc cref="RegisterInitializerRequests"/>
-    [RequiresUnreferencedCode("Serializes object to json")]
     public void RegisterInitializerRequests(HandlerWrapper handlerWrapper)
     {
-        #if NET8_0_OR_GREATER
-
         Amazon.Lambda.Core.SnapshotRestore.RegisterBeforeSnapshot(async () =>
         {
             // Construct specialized HttpClient that will intercept requests and saved them inside
@@ -60,39 +60,36 @@ public void RegisterInitializerRequests(HandlerWrapper handlerWrapper)
 
             // Request are now in CapturedHttpRequests.  Serialize each one into a json object
             // and execute the request through the lambda pipeline (ie handlerWrapper).
-            foreach (var req in LambdaSnapstartInitializerHttpMessageHandler.CapturedHttpRequests)
+            foreach (var json in LambdaSnapstartInitializerHttpMessageHandler.CapturedHttpRequestsJson)
             {
-                var json = JsonSerializer.Serialize(req);
-
                 await SnapstartHelperLambdaRequests.ExecuteSnapstartInitRequests(json, times: 5, handlerWrapper);
             }
         });
-
-        #endif
     }
 
+    
     /// <inheritdoc cref="ServiceCollectionExtensions.AddAWSLambdaBeforeSnapshotRequest"/>
     internal static BeforeSnapstartRequestRegistrar Registrar = new();
 
     internal class BeforeSnapstartRequestRegistrar
     {
-        private List<Func<HttpClient, Task>> beforeSnapstartFuncs = new();
+        private readonly List<Func<HttpClient, Task>> _beforeSnapstartFuncs = new();
 
         public void Register(Func<HttpClient, Task> beforeSnapstartRequest)
         {
-            beforeSnapstartFuncs.Add(beforeSnapstartRequest);
+            _beforeSnapstartFuncs.Add(beforeSnapstartRequest);
         }
 
         internal async Task Execute(HttpClient client)
         {
-            foreach (var f in beforeSnapstartFuncs)
+            foreach (var f in _beforeSnapstartFuncs)
                 await f(client);
         }
     }
 
     private static class SnapstartHelperLambdaRequests
     {
-        private static InternalLogger _logger = InternalLogger.GetDefaultLogger();
+        private static readonly InternalLogger _logger = InternalLogger.GetDefaultLogger();
 
         private static readonly RuntimeApiHeaders _fakeRuntimeApiHeaders = new(new Dictionary<string, IEnumerable<string>>
         {
@@ -136,7 +133,7 @@ private class LambdaSnapstartInitializerHttpMessageHandler : HttpMessageHandler
 
         public static Uri BaseUri { get; } = new Uri("http://localhost");
 
-        public static List<object> CapturedHttpRequests { get; } = new();
+        public static List<string> CapturedHttpRequestsJson { get; } = new();
 
         public LambdaSnapstartInitializerHttpMessageHandler(LambdaEventSource lambdaEventSource)
         {
@@ -162,49 +159,60 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
                 Query = QueryHelpers.ParseNullableQuery(request.RequestUri?.Query)
             };
 
-            object translatedRequest = _lambdaEventSource switch
+            string translatedRequestJson = _lambdaEventSource switch
             {
-                LambdaEventSource.ApplicationLoadBalancer => new ApplicationLoadBalancerRequest
-                {
-                    Body = duckRequest.Body,
-                    Headers = duckRequest.Headers,
-                    Path = duckRequest.Path,
-                    HttpMethod = duckRequest.HttpMethod,
-                    QueryStringParameters = duckRequest.Query?.ToDictionary(k => k.Key, v => v.Value.ToString())
-                },
-                LambdaEventSource.HttpApi => new APIGatewayHttpApiV2ProxyRequest
-                {
-                    Body = duckRequest.Body,
-                    Headers = duckRequest.Headers,
-                    RawPath = duckRequest.Path,
-                    RequestContext = new APIGatewayHttpApiV2ProxyRequest.ProxyRequestContext
-                    {
-                        Http = new APIGatewayHttpApiV2ProxyRequest.HttpDescription
+                LambdaEventSource.ApplicationLoadBalancer =>
+                    JsonSerializer.Serialize(
+                        new ApplicationLoadBalancerRequest
                         {
-                            Method = duckRequest.HttpMethod,
-                            Path = duckRequest.Path
-                        }
-                    },
-                    QueryStringParameters = duckRequest.Query?.ToDictionary(k => k.Key, v => v.Value.ToString()),
-                    RawQueryString = duckRequest.RawQuery
-                },
-                LambdaEventSource.RestApi => new APIGatewayProxyRequest
-                {
-                    Body = duckRequest.Body,
-                    Headers = duckRequest.Headers,
-                    Path = duckRequest.Path,
-                    HttpMethod = duckRequest.HttpMethod,
-                    RequestContext = new APIGatewayProxyRequest.ProxyRequestContext
-                    {
-                        HttpMethod = duckRequest.HttpMethod
-                    },
-                    QueryStringParameters = duckRequest.Query?.ToDictionary(k => k.Key, v => v.Value.ToString())
-                },
+                            Body = duckRequest.Body,
+                            Headers = duckRequest.Headers,
+                            Path = duckRequest.Path,
+                            HttpMethod = duckRequest.HttpMethod,
+                            QueryStringParameters = duckRequest.Query?.ToDictionary(k => k.Key, v => v.Value.ToString())
+                        },
+                        LambdaRequestTypeClasses.Default.ApplicationLoadBalancerRequest),
+                LambdaEventSource.HttpApi =>
+                    JsonSerializer.Serialize(
+                        new APIGatewayHttpApiV2ProxyRequest
+                        {
+                            Body = duckRequest.Body,
+                            Headers = duckRequest.Headers,
+                            RawPath = duckRequest.Path,
+                            RequestContext = new APIGatewayHttpApiV2ProxyRequest.ProxyRequestContext
+                            {
+                                Http = new APIGatewayHttpApiV2ProxyRequest.HttpDescription
+                                {
+                                    Method = duckRequest.HttpMethod,
+                                    Path = duckRequest.Path
+                                }
+                            },
+                            QueryStringParameters = duckRequest.Query?.ToDictionary(k => k.Key, v => v.Value.ToString()),
+                            RawQueryString = duckRequest.RawQuery
+                        },
+                        LambdaRequestTypeClasses.Default.APIGatewayHttpApiV2ProxyRequest),
+                LambdaEventSource.RestApi =>
+                    JsonSerializer.Serialize(
+                        new APIGatewayProxyRequest
+                        {
+                            Body = duckRequest.Body,
+                            Headers = duckRequest.Headers,
+                            Path = duckRequest.Path,
+                            HttpMethod = duckRequest.HttpMethod,
+                            RequestContext = new APIGatewayProxyRequest.ProxyRequestContext
+                            {
+                                HttpMethod = duckRequest.HttpMethod
+                            },
+                            QueryStringParameters = duckRequest.Query?.ToDictionary(k => k.Key, v => v.Value.ToString())
+                        },
+                        LambdaRequestTypeClasses.Default.APIGatewayProxyRequest),
                 _ => throw new NotImplementedException(
                     $"Unknown {nameof(LambdaEventSource)}: {Enum.GetName(_lambdaEventSource)}")
             };
 
-            CapturedHttpRequests.Add(translatedRequest);
+            // NOTE: Any object added to CapturedHttpRequests must have it's type added
+            // to the 
+            CapturedHttpRequestsJson.Add(translatedRequestJson);
 
             return new HttpResponseMessage(HttpStatusCode.OK);
         }
@@ -218,3 +226,14 @@ private async Task<string> ReadContent(HttpRequestMessage r)
         }
     }
 }
+
+
+[JsonSourceGenerationOptions(WriteIndented = true)]
+[JsonSerializable(typeof(ApplicationLoadBalancerRequest))]
+[JsonSerializable(typeof(APIGatewayHttpApiV2ProxyRequest))]
+[JsonSerializable(typeof(APIGatewayProxyRequest))]
+
+internal partial class LambdaRequestTypeClasses : JsonSerializerContext
+{
+}
+#endif

Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/ServiceCollectionExtensions.cs

@@ -88,6 +88,7 @@ public static IServiceCollection AddAWSLambdaHosting(this IServiceCollection ser
             return services;
         }
 
+#if NET8_0_OR_GREATER
         /// <summary>
         /// Adds a function meant to initialize the asp.net and lambda pipelines during <see cref="SnapshotRestore.RegisterBeforeSnapshot"/>
         /// improving the performance gains offered by SnapStart.
@@ -123,9 +124,17 @@ public static IServiceCollection AddAWSLambdaHosting(this IServiceCollection ser
         /// ]]>
         /// </code>
         /// </summary>
+        #else
+        /// <summary>
+        /// Snapstart requires your application to target .NET 8 or above.
+        /// </summary>
+        #endif
         public static IServiceCollection AddAWSLambdaBeforeSnapshotRequest(this IServiceCollection services, Func<HttpClient, Task> beforeSnapStartRequest)
         {
+
+            #if NET8_0_OR_GREATER
             LambdaSnapstartExecuteRequestsBeforeSnapshotHelper.Registrar.Register(beforeSnapStartRequest);
+            #endif
 
             return services;
         }
@@ -153,8 +162,10 @@ private static bool TryLambdaSetup(IServiceCollection services, LambdaEventSourc
 
             Utilities.EnsureLambdaServerRegistered(services, serverType);
 
+            #if NET8_0_OR_GREATER
             // register a LambdaSnapStartInitializerHttpMessageHandler
             services.AddSingleton<LambdaSnapstartExecuteRequestsBeforeSnapshotHelper>(new LambdaSnapstartExecuteRequestsBeforeSnapshotHelper(eventSource));
+            #endif
 
             return true;
         }