c++: AWS S3 Object Lambda - c++

Question

AWS recently introduced S3 Object Lambda, however looking at the online documentation:
Writing and debugging Lambda functions for S3 Object Lambda Access Points
Introducing Amazon S3 Object Lambda – Use Your Code to Process Data as It Is Being Retrieved from S3
How to use Amazon S3 Object Lambda to generate thumbnails
I can only find example for Java, Python and NodeJS.
Is there an example out there for c++ that I missed ? In particular I fail to understand what is the equivalent in c++ for getObjectContext (python/nodejs) / S3ObjectLambdaEvent (java) ? How should I retrieve outputRoute, outputToken, inputS3Url ? The integration test does not make it particularly clear either:
https://github.com/aws/aws-sdk-cpp/blob/main/aws-cpp-sdk-s3-integration-tests/BucketAndObjectOperationTest.cpp#L580-L581

Answer 1

S3 Object Lambda is using the AWS Lambda service. AWS Lambda does only support the following runtimes "natively":
Go
.NET Core
Ruby
Java
Python
NodeJS
C++ is support through "custom" runtimes or through Docker containers. Usually, the AWS documentation only covers the "natively" supported runtimes and even then not all (as you noticed). Mostly they have examples for the most popular ones.
So what you need to look for are C++ Lambda examples, examples using the C++ AWS SDK and reference documentation.
Using the reference documentation and the Java/Python/NodeJS examples, it should be easy to write a C++ version.
For example:
Introducing the C++ Lambda Runtime (Blog Post)
C++ AWS SDK Page
API Reference for WriteGetObjectResponseRequest

Answer 2

Answering my own post after a couple of weeks of struggle.
Basic point is summarized at Introduction to Amazon S3 Object Lambda
The JSON payload of interest is simply:
{ "xAmzRequestId": "1a5ed718-5f53-471d-b6fe-5cf62d88d02a",
"getObjectContext": {
"inputS3Url": "https://transform-424432388155.s3-accesspoint.us-east-1.amazonaws.com/title.txt?X-Amz-Security-Token=...",
"outputRoute": "io-iad-cell001",
"outputToken": "..." },
You can simply open it using:
static invocation_response my_handler(invocation_request const& req, Aws::S3::S3Client const& client)
{
using namespace Aws::Utils::Json;
JsonValue json(req.payload);
if (!json.WasParseSuccessful()) {
return invocation_response::failure("Failed to parse input JSON", "InvalidJSON");
}
auto view = json.View();
auto s3url = view.GetObject("getObjectContext").GetString("inputS3Url");
auto route = view.GetObject("getObjectContext").GetString("outputRoute");
auto token = view.GetObject("getObjectContext").GetString("outputToken");
Which will later be used in WriteGetObjectResponseRequest as:
S3::Model::WriteGetObjectResponseRequest request;
request.WithRequestRoute(route);
request.WithRequestToken(token);
request.SetBody(objectStream);
auto outcome = client.WriteGetObjectResponse(request);
It is then up to the application to decide on how to construct the objectStream, but a simple pass-through example would be:
std::shared_ptr<Aws::Http::HttpRequest> getRequest =
CreateHttpRequest(s3url, Http::HttpMethod::HTTP_GET,
Aws::Utils::Stream::DefaultResponseStreamFactoryMethod);
std::shared_ptr<Aws::Http::HttpClient> httpClient =
Aws::Http::CreateHttpClient(Aws::Client::ClientConfiguration());
std::shared_ptr<Aws::Http::HttpResponse> getResponse =
httpClient->MakeRequest(getRequest);
std::shared_ptr<Aws::IOStream> objectStream =
Aws::MakeShared<Aws::StringStream>("SO-WriteGetObjectResponse");
const Aws::IOStream& responseBody = getResponse->GetResponseBody();
*objectStream << responseBody.rdbuf();
objectStream->flush();
Examples which help me are:
https://github.com/awslabs/aws-lambda-cpp/blob/master/examples/s3/main.cpp
Working with WriteGetObjectResponse (Example #2/Python)