AWS Lambda C++ download file from s3

#include <aws/core/Aws.h>
#include <aws/core/utils/logging/LogLevel.h>
#include <aws/core/utils/logging/ConsoleLogSystem.h>
#include <aws/core/utils/logging/LogMacros.h>
#include <aws/core/utils/json/JsonSerializer.h>
#include <aws/core/utils/HashingUtils.h>
#include <aws/core/platform/Environment.h>
#include <aws/core/client/ClientConfiguration.h>
#include <aws/core/auth/AWSCredentialsProvider.h>
#include <aws/s3/S3Client.h>
#include <aws/s3/model/GetObjectRequest.h>
#include <aws/lambda-runtime/runtime.h>
#include <iostream>
#include <memory>
#include <fstream>

using namespace aws::lambda_runtime;


char const TAG[] = "LAMBDA_ALLOC";

enum class Status {
    Success,
    Failure
};

std::string download_file(Aws::S3::S3Client const& client,
                          Aws::String       const& bucket,
                          Aws::String       const& key,
                          Aws::String            & output)
{
    Aws::S3::Model::GetObjectRequest request;

    request.WithBucket(bucket).WithKey(key);

    auto outcome = client.GetObject(request);
    if (outcome.IsSuccess()) {
        AWS_LOGSTREAM_INFO(TAG, "Download completed!");

        Aws::StringStream ss;
        ss << outcome.GetResult().GetBody().rdbuf();

        output = ss.str();
        return "";
    }else {
        AWS_LOGSTREAM_ERROR(TAG, "Failed with error: " << outcome.GetError());
        return outcome.GetError().GetMessage();
    }
}

static invocation_response getResponse(Status status, const std::string& body) {
    Aws::Utils::Json::JsonValue response;
    response.WithString("body", body.c_str()).WithInteger("statusCode", 200);
    std::string payload = response.View().WriteCompact();

    if (status == Status::Failure) return invocation_response::success(payload, "");
    else return invocation_response::success(payload, "application/json");
}

static invocation_response my_handler(invocation_request const& req, Aws::S3::S3Client const& client) {
    Aws::Utils::Json::JsonValue json(req.payload);
    if (!json.WasParseSuccessful()) {
        return getResponse(Status::Failure, "InvalidJSON: Failed to parse input JSON");
    }

    return getResponse(Status::Failure, a);

    auto query = json.View().GetObject("queryStringParameters");

    if (!query.ValueExists("s3bucket") || !query.GetObject("s3bucket").IsString() ||
        !query.ValueExists("s3key")    || !query.GetObject("s3key").IsString())
    {
        return getResponse(Status::Failure, "InvalidJSON: Missing input value s3bucket or s3key");
    }

    auto bucket = query.GetString("s3bucket");
    auto key    = query.GetString("s3key");

    AWS_LOGSTREAM_INFO(TAG, "Attempting to download file from s3://" << bucket << "/" << key);

    Aws::String file;
    auto err = download_file(client, bucket, key, file);
    if (!err.empty()) {
        return getResponse(Status::Failure, std::string("DownloadFailure: ") + err);
    }

    return getResponse(Status::Success, file);
}


std::function<std::shared_ptr<Aws::Utils::Logging::LogSystemInterface>()> GetConsoleLoggerFactory()
{
    return [] {
        return Aws::MakeShared<Aws::Utils::Logging::ConsoleLogSystem>(
            "console_logger", Aws::Utils::Logging::LogLevel::Trace);
    };
}


int main() {
    using namespace Aws;
    SDKOptions options;
    options.loggingOptions.logLevel = Aws::Utils::Logging::LogLevel::Info;
    options.loggingOptions.logger_create_fn = GetConsoleLoggerFactory();
    InitAPI(options);
    {
        Client::ClientConfiguration config;
        config.region = Aws::Environment::GetEnv("AWS_REGION");
        config.caFile = "/etc/pki/tls/certs/ca-bundle.crt";

        auto credentialsProvider = Aws::MakeShared<Aws::Auth::EnvironmentAWSCredentialsProvider>(TAG);
        S3::S3Client client(credentialsProvider, config);
        auto handler_fn = [&client](aws::lambda_runtime::invocation_request const& req) {
            return my_handler(req, client);
        };
        run_handler(handler_fn);
    }
    ShutdownAPI(options);
    return 0;
}