Add support for Lambda Response Streaming

[normj]

Issue #, if available:
#1635

Description of changes:
Integrate Lambda response streaming support into the Amazon.Lambda.RuntimeSupport.

A hello world example of using response streaming. In this case sense I wrapped the Stream returned from CreateStream in a StreamWriter the writes will be buffered in StreamWriter till the buffer is full. I call the flush method every 10 iterations to force sending data back to the client.

using Amazon.Lambda.Core;
using Amazon.Lambda.Core.ResponseStreaming;
using Amazon.Lambda.RuntimeSupport;
using Amazon.Lambda.Serialization.SystemTextJson;

#pragma warning disable CA2252

// The function handler that will be called for each Lambda event
var handler = async (string input, ILambdaContext context) =>
{
    using var responseStream = LambdaResponseStreamFactory.CreateStream();

    using var writer = new StreamWriter(responseStream);
    for (var i = 1; i <= 100; i++)
    {
        var message = $"Hello {input} - {i}";
        await writer.WriteLineAsync(message);

        if (i % 10 == 0)
        {
            await writer.FlushAsync();
            await Task.Delay(1000);
        }
    }
};

// Build the Lambda runtime client passing in the handler to call for each
// event and the JSON serializer to use for translating Lambda JSON documents
// to .NET types.
await LambdaBootstrapBuilder.Create(handler, new DefaultLambdaJsonSerializer())
        .Build()
        .RunAsync();

For a use with API Gateway or Lambda Function URL you need to create the stream with the CreateHttpStream passing the status code and response headers.

using Amazon.Lambda.APIGatewayEvents;
using Amazon.Lambda.Core;
using Amazon.Lambda.Core.ResponseStreaming;
using Amazon.Lambda.RuntimeSupport;
using Amazon.Lambda.Serialization.SystemTextJson;
using System.Net;

#pragma warning disable CA2252

// The function handler that will be called for each Lambda event
var handler = async (APIGatewayProxyRequest request, ILambdaContext context) =>
{
    var prelude = new HttpResponseStreamPrelude
    {
        StatusCode = HttpStatusCode.OK,
        Headers =
        {
            { "Content-Type", "text/plain" }
        }
    };
   
    using var responseStream = LambdaResponseStreamFactory.CreateHttpStream(prelude);

    using var writer = new StreamWriter(responseStream);
    for (var i = 1; i <= 10000000; i++)
    {
        var message = $"Hello - {i} ({responseStream.Length.ToString("N0")}) (Remaining Time: {context.RemainingTime})";
        await writer.WriteLineAsync(message);

        if (i % 100 == 0)
        {
            await writer.FlushAsync();
        }

        if (context.RemainingTime < TimeSpan.FromSeconds(5))
        {
            await writer.WriteLineAsync("Approaching Lambda timeout, stopping the stream.");
            await writer.FlushAsync();
            break;
        }
    }
};

// Build the Lambda runtime client passing in the handler to call for each
// event and the JSON serializer to use for translating Lambda JSON documents
// to .NET types.
await LambdaBootstrapBuilder.Create(handler, new DefaultLambdaJsonSerializer())
        .Build()
        .RunAsync();

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[GarrettBeatty]

why default to 80 over 443? just because its http and not https?

[normj]

Reality is there should always be a port defined in hostAndPort. Change the code to not have a default and throw an error if port is not set.

[GarrettBeatty]

nit: make constant since its used multiple times

[normj]

Done

[GarrettBeatty]

whats 16384 here? can you add a comment

[normj]

Added comment but the value is an arbitrary safety net value.

[GarrettBeatty]

why did we have to disable parallelization?

[normj]

I was probably dealing with some test instability. I removed the flag and tests were successful form. See if the GitHub checks are successful with the flag removed.

[philasmar]

nit: could you give more context as to why the prelude is needed?

[normj]

Done

[philasmar]

nit: all docs for the fields of this class has "to include in the response prelude.". It feels redundant.

[normj]

Removed

[philasmar]

is there a reason why both are needed? why not just have 1 that supports multi value?

[normj]

For API Gateway REST APIs the JSON for the prelude must use MultiValueHeaders but Lambda URLs you have to use Headers. The properties here are 1 to 1 mirror of the union of the specs for API Gateway Rest APIs and Function URLs. If API Gateway HTTP APIs ever support they would probably require the Headers collection. At the point of generating the JSON via the ToByteArray we don't have the context to say what is the event source. It is up to the user to know which one to use.

I updated the docs for the properties to call out when to use the properties.

[philasmar]

nit: remove extra whitespace

[normj]

Done

[philasmar]

nit: remove extra whitespace

[normj]

Done

[philasmar]

should we be measuring the performance of this HTTP client against the default one?

[normj]

The default HTTP client doesn't work for this scenario hence the reason we have to use our custom implementation.

[philasmar]

do we want to make this customizable by the user?

[normj]

No, this is just a sanity check but it should never be reached unless we have a bug. Plus this is more of an implementation detail that users won't understand and by exposing a config it makes this implementation detail part of our public API contract.