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Add support for Lambda Response Streaming in ASP.NET Core bridge packages #2293

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8acb864
Initial ASP.NET Core response streaming
normj Mar 8, 2026
64ad36a
Add support for Lambda Response Streaming in ASP.NET Core bridge libr…
normj Mar 10, 2026
694c176
Merge branch 'normj/response-streaming' into normj/aspnetcore-respons…
normj Mar 12, 2026
e9f7dd7
Update preview flag with message
normj Mar 12, 2026
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27 changes: 27 additions & 0 deletions .autover/changes/f0d5a912-bcfa-4244-96cb-ac3c847f877c.json
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@@ -0,0 +1,27 @@
{
"Projects": [
{
"Name": "Amazon.Lambda.AspNetCoreServer",
"Type": "Major",
"ChangelogMessages": [
"[Breaking] Update build targets from .NET 6 and 8 to .NET 8 and 10",
"[Preview] Add support Lambda Response Streaming enabled by setting the EnableResponseStreaming property from the base class AbstractAspNetCoreFunction"
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Copilot AI Mar 12, 2026

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Changelog message grammar: "Add support Lambda Response Streaming enabled by setting..." is missing "for" and reads awkwardly. Consider rephrasing to something like "[Preview] Add support for Lambda response streaming, enabled by setting the EnableResponseStreaming property on AbstractAspNetCoreFunction" for clarity.

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]
},
{
"Name": "Amazon.Lambda.AspNetCoreServer.Hosting",
"Type": "Major",
"ChangelogMessages": [
"[Breaking] Update build targets from .NET 6 and 8 to .NET 8 and 10",
"[Preview] Add support Lambda Response Streaming enabled by setting the EnableResponseStreaming property on the HostingOptions object passed into the AddAWSLambdaHosting method"
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Copilot AI Mar 12, 2026

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Changelog message grammar: "Add support Lambda Response Streaming enabled by setting..." is missing "for" and would be clearer if rephrased. Consider something like "[Preview] Add support for Lambda response streaming, enabled by setting EnableResponseStreaming on HostingOptions passed to AddAWSLambdaHosting".

Copilot uses AI. Check for mistakes.
]
},
{
"Name": "Amazon.Lambda.Logging.AspNetCore",
"Type": "Major",
"ChangelogMessages": [
"[Breaking] Update build targets from .NET 6 and 8 to .NET 8 and 10"
]
}
]
}
2 changes: 1 addition & 1 deletion .../src/Amazon.Lambda.AspNetCoreServer.Hosting/Amazon.Lambda.AspNetCoreServer.Hosting.csproj
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Expand Up @@ -4,7 +4,7 @@

<PropertyGroup>
<Description>Package for running ASP.NET Core applications using the Minimal API style as a AWS Lambda function.</Description>
<TargetFrameworks>net6.0;net8.0</TargetFrameworks>
<TargetFrameworks>net8.0;net10.0</TargetFrameworks>
<ImplicitUsings>enable</ImplicitUsings>
<Nullable>enable</Nullable>
<Version>1.10.0</Version>
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14 changes: 14 additions & 0 deletions Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/HostingOptions.cs
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Expand Up @@ -9,6 +9,12 @@ namespace Amazon.Lambda.AspNetCoreServer.Hosting;
/// </summary>
public class HostingOptions
{
internal const string ParameterizedPreviewMessage =
"Response streaming is in preview till a new version of .NET Lambda runtime client that supports response streaming " +
"has been deployed to the .NET Lambda managed runtime. Till deployment has been made the feature can be used by deploying as an " +
"executable including the latest version of Amazon.Lambda.RuntimeSupport and setting the \"EnablePreviewFeatures\" in the Lambda " +
"project file to \"true\"";

/// <summary>
/// The ILambdaSerializer used by Lambda to convert the incoming event JSON into the .NET event type and serialize the .NET response type
/// back to JSON to return to Lambda.
Expand All @@ -27,6 +33,14 @@ public class HostingOptions
/// </summary>
public bool IncludeUnhandledExceptionDetailInResponse { get; set; } = false;

/// <summary>
/// When true, the Lambda hosting server will invoke <c>StreamingFunctionHandlerAsync</c>
/// instead of <c>FunctionHandlerAsync</c>, enabling Lambda response streaming.
/// Requires net8.0 or later.
Comment on lines +37 to +39
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The XML doc for EnableResponseStreaming mentions invoking StreamingFunctionHandlerAsync, but the implementation toggles behavior inside FunctionHandlerAsync via the EnableResponseStreaming property (no StreamingFunctionHandlerAsync method exists). This doc mismatch may confuse users; consider updating the comment to describe the actual behavior (FunctionHandlerAsync switches to streaming mode and returns null while writing to a Lambda response stream).

Suggested change
/// When true, the Lambda hosting server will invoke <c>StreamingFunctionHandlerAsync</c>
/// instead of <c>FunctionHandlerAsync</c>, enabling Lambda response streaming.
/// Requires net8.0 or later.
/// When true, the Lambda hosting server enables Lambda response streaming behavior
/// when invoking <c>FunctionHandlerAsync</c>. In streaming mode,
/// <c>FunctionHandlerAsync</c> writes directly to the Lambda response stream and
/// returns <c>null</c>. Requires net8.0 or later.

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/// </summary>
[System.Runtime.Versioning.RequiresPreviewFeatures(ParameterizedPreviewMessage)]
public bool EnableResponseStreaming { get; set; } = false;

/// <summary>
/// Callback invoked after request marshalling to customize the HTTP request feature.
/// Receives the IHttpRequestFeature, Lambda request object, and ILambdaContext.
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2 changes: 0 additions & 2 deletions ...src/Amazon.Lambda.AspNetCoreServer.Hosting/Internal/GetBeforeSnapshotRequestsCollector.cs
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Expand Up @@ -5,7 +5,6 @@

namespace Amazon.Lambda.AspNetCoreServer.Hosting.Internal;

#if NET8_0_OR_GREATER
/// <summary>
/// Helper class for storing Requests for
/// <see cref="ServiceCollectionExtensions.AddAWSLambdaBeforeSnapshotRequest"/>
Expand All @@ -14,4 +13,3 @@ internal class GetBeforeSnapshotRequestsCollector
{
public HttpRequestMessage? Request { get; set; }
}
#endif
45 changes: 21 additions & 24 deletions Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/Internal/LambdaRuntimeSupportServer.cs
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Expand Up @@ -78,18 +78,21 @@ public APIGatewayHttpApiV2LambdaRuntimeSupportServer(IServiceProvider servicePro
/// <returns></returns>
protected override HandlerWrapper CreateHandlerWrapper(IServiceProvider serviceProvider)
{
var handler = new APIGatewayHttpApiV2MinimalApi(serviceProvider).FunctionHandlerAsync;
return HandlerWrapper.GetHandlerWrapper(handler, this.Serializer);
var handler = new APIGatewayHttpApiV2MinimalApi(serviceProvider);
#pragma warning disable CA2252
var hostingOptions = serviceProvider.GetService<HostingOptions>();
handler.EnableResponseStreaming = hostingOptions?.EnableResponseStreaming ?? false;
#pragma warning restore CA2252
Func<APIGatewayEvents.APIGatewayHttpApiV2ProxyRequest, ILambdaContext, Task<APIGatewayEvents.APIGatewayHttpApiV2ProxyResponse>> bufferedHandler = handler.FunctionHandlerAsync;
return HandlerWrapper.GetHandlerWrapper(bufferedHandler, this.Serializer);
}

/// <summary>
/// Create the APIGatewayHttpApiV2ProxyFunction passing in the ASP.NET Core application's IServiceProvider
/// </summary>
public class APIGatewayHttpApiV2MinimalApi : APIGatewayHttpApiV2ProxyFunction
{
#if NET8_0_OR_GREATER
private readonly IEnumerable<GetBeforeSnapshotRequestsCollector> _beforeSnapshotRequestsCollectors;
#endif
private readonly HostingOptions? _hostingOptions;

/// <summary>
Expand All @@ -99,9 +102,7 @@ public class APIGatewayHttpApiV2MinimalApi : APIGatewayHttpApiV2ProxyFunction
public APIGatewayHttpApiV2MinimalApi(IServiceProvider serviceProvider)
: base(serviceProvider)
{
#if NET8_0_OR_GREATER
_beforeSnapshotRequestsCollectors = serviceProvider.GetServices<GetBeforeSnapshotRequestsCollector>();
#endif

// Retrieve HostingOptions from service provider (may be null for backward compatibility)
_hostingOptions = serviceProvider.GetService<HostingOptions>();
Expand All @@ -127,14 +128,12 @@ public APIGatewayHttpApiV2MinimalApi(IServiceProvider serviceProvider)
}
}

#if NET8_0_OR_GREATER
protected override IEnumerable<HttpRequestMessage> GetBeforeSnapshotRequests()
{
foreach (var collector in _beforeSnapshotRequestsCollectors)
if (collector.Request != null)
yield return collector.Request;
}
#endif

protected override void PostMarshallRequestFeature(IHttpRequestFeature aspNetCoreRequestFeature, APIGatewayEvents.APIGatewayHttpApiV2ProxyRequest lambdaRequest, ILambdaContext lambdaContext)
{
Expand Down Expand Up @@ -208,18 +207,21 @@ public APIGatewayRestApiLambdaRuntimeSupportServer(IServiceProvider serviceProvi
/// <returns></returns>
protected override HandlerWrapper CreateHandlerWrapper(IServiceProvider serviceProvider)
{
var handler = new APIGatewayRestApiMinimalApi(serviceProvider).FunctionHandlerAsync;
return HandlerWrapper.GetHandlerWrapper(handler, this.Serializer);
var handler = new APIGatewayRestApiMinimalApi(serviceProvider);
#pragma warning disable CA2252
var hostingOptions = serviceProvider.GetService<HostingOptions>();
handler.EnableResponseStreaming = hostingOptions?.EnableResponseStreaming ?? false;
#pragma warning restore CA2252
Func<APIGatewayEvents.APIGatewayProxyRequest, ILambdaContext, Task<APIGatewayEvents.APIGatewayProxyResponse>> bufferedHandler = handler.FunctionHandlerAsync;
return HandlerWrapper.GetHandlerWrapper(bufferedHandler, this.Serializer);
}

/// <summary>
/// Create the APIGatewayProxyFunction passing in the ASP.NET Core application's IServiceProvider
/// </summary>
public class APIGatewayRestApiMinimalApi : APIGatewayProxyFunction
{
#if NET8_0_OR_GREATER
private readonly IEnumerable<GetBeforeSnapshotRequestsCollector> _beforeSnapshotRequestsCollectors;
#endif
private readonly HostingOptions? _hostingOptions;

/// <summary>
Expand All @@ -229,9 +231,7 @@ public class APIGatewayRestApiMinimalApi : APIGatewayProxyFunction
public APIGatewayRestApiMinimalApi(IServiceProvider serviceProvider)
: base(serviceProvider)
{
#if NET8_0_OR_GREATER
_beforeSnapshotRequestsCollectors = serviceProvider.GetServices<GetBeforeSnapshotRequestsCollector>();
#endif

// Retrieve HostingOptions from service provider (may be null for backward compatibility)
_hostingOptions = serviceProvider.GetService<HostingOptions>();
Expand All @@ -257,14 +257,12 @@ public APIGatewayRestApiMinimalApi(IServiceProvider serviceProvider)
}
}

#if NET8_0_OR_GREATER
protected override IEnumerable<HttpRequestMessage> GetBeforeSnapshotRequests()
{
foreach (var collector in _beforeSnapshotRequestsCollectors)
if (collector.Request != null)
yield return collector.Request;
}
#endif

protected override void PostMarshallRequestFeature(IHttpRequestFeature aspNetCoreRequestFeature, APIGatewayEvents.APIGatewayProxyRequest lambdaRequest, ILambdaContext lambdaContext)
{
Expand Down Expand Up @@ -338,18 +336,21 @@ public ApplicationLoadBalancerLambdaRuntimeSupportServer(IServiceProvider servic
/// <returns></returns>
protected override HandlerWrapper CreateHandlerWrapper(IServiceProvider serviceProvider)
{
var handler = new ApplicationLoadBalancerMinimalApi(serviceProvider).FunctionHandlerAsync;
return HandlerWrapper.GetHandlerWrapper(handler, this.Serializer);
var handler = new ApplicationLoadBalancerMinimalApi(serviceProvider);
#pragma warning disable CA2252
var hostingOptions = serviceProvider.GetService<HostingOptions>();
handler.EnableResponseStreaming = hostingOptions?.EnableResponseStreaming ?? false;
#pragma warning restore CA2252
Func<ApplicationLoadBalancerEvents.ApplicationLoadBalancerRequest, ILambdaContext, Task<ApplicationLoadBalancerEvents.ApplicationLoadBalancerResponse>> bufferedHandler = handler.FunctionHandlerAsync;
return HandlerWrapper.GetHandlerWrapper(bufferedHandler, this.Serializer);
}

/// <summary>
/// Create the ApplicationLoadBalancerFunction passing in the ASP.NET Core application's IServiceProvider
/// </summary>
public class ApplicationLoadBalancerMinimalApi : ApplicationLoadBalancerFunction
{
#if NET8_0_OR_GREATER
private readonly IEnumerable<GetBeforeSnapshotRequestsCollector> _beforeSnapshotRequestsCollectors;
#endif
private readonly HostingOptions? _hostingOptions;

/// <summary>
Expand All @@ -359,9 +360,7 @@ public class ApplicationLoadBalancerMinimalApi : ApplicationLoadBalancerFunction
public ApplicationLoadBalancerMinimalApi(IServiceProvider serviceProvider)
: base(serviceProvider)
{
#if NET8_0_OR_GREATER
_beforeSnapshotRequestsCollectors = serviceProvider.GetServices<GetBeforeSnapshotRequestsCollector>();
#endif

// Retrieve HostingOptions from service provider (may be null for backward compatibility)
_hostingOptions = serviceProvider.GetService<HostingOptions>();
Expand All @@ -387,14 +386,12 @@ public ApplicationLoadBalancerMinimalApi(IServiceProvider serviceProvider)
}
}

#if NET8_0_OR_GREATER
protected override IEnumerable<HttpRequestMessage> GetBeforeSnapshotRequests()
{
foreach (var collector in _beforeSnapshotRequestsCollectors)
if (collector.Request != null)
yield return collector.Request;
}
#endif

protected override void PostMarshallRequestFeature(IHttpRequestFeature aspNetCoreRequestFeature, ApplicationLoadBalancerEvents.ApplicationLoadBalancerRequest lambdaRequest, ILambdaContext lambdaContext)
{
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2 changes: 0 additions & 2 deletions Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/ServiceCollectionExtensions.cs
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Expand Up @@ -88,7 +88,6 @@ public static IServiceCollection AddAWSLambdaHosting(this IServiceCollection ser
return services;
}

#if NET8_0_OR_GREATER
/// <summary>
/// Adds a <see cref="HttpRequestMessage"/>> that will be used to invoke
/// Routes in your lambda function in order to initialize the ASP.NET Core and Lambda pipelines
Expand Down Expand Up @@ -142,7 +141,6 @@ public static IServiceCollection AddAWSLambdaBeforeSnapshotRequest(this IService

return services;
}
#endif

private static bool TryLambdaSetup(IServiceCollection services, LambdaEventSource eventSource, Action<HostingOptions>? configure, out HostingOptions? hostingOptions)
{
Expand Down
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