Downloads a .json.gz file from S3, uncompresses it and converts it to json using nlohmann::json

aws_json_gz_downloader.hpp

#pragma once

#include <aws/core/Aws.h>
#include <aws/core/client/ClientConfiguration.h>
#include <aws/core/auth/AWSCredentialsProviderChain.h>
#include <aws/core/utils/logging/LogLevel.h>
#include <aws/s3/S3Client.h>
#include <aws/s3/model/GetObjectRequest.h>
#include <iostream>
#include <fstream>
#include <memory>

// decompress.hpp from https://github.com/mapbox/gzip-hpp/blob/master/include/gzip/
#include "decompress.hpp"
// nlohmann::json lib
#include "json.hpp"

using json = nlohmann::json;

using std::clog, std::endl;
using namespace Aws;

// Uncompressed gzipped string from stream
std::string uncompressed_string_from_stream(std::basic_iostream<char>& stream)
{
    // Read data from the stream
    stream.seekg (0, stream.end);
    int length = stream.tellg();
    stream.seekg (0, stream.beg);
    char * buffer = new char [length];
    stream.read (buffer,length);

    // Uncompress the data
    std::string result = gzip::decompress(buffer, length);

    // Delete the buffer and return the result
    delete buffer;
    return result;
}

// Downloads a .json.gz file from S3, uncompresses it and converts it to json using nlohmann::json
json download_json(String profile, String region, String bucket, String key)//, String local_path)
{
    json json_result = nullptr;
    SDKOptions options;
    InitAPI(options);
    {
        Client::ClientConfiguration config;
        config.region = region;
        config.scheme = Http::Scheme::HTTPS;

        auto credentials = Auth::ProfileConfigFileAWSCredentialsProvider(profile.c_str()).GetAWSCredentials();
        auto client = S3::S3Client(credentials, config);

        S3::Model::GetObjectRequest request;
        request.WithBucket(bucket).WithKey(key);
        //request.SetResponseStreamFactory([local_path] { return new std::fstream(local_path.c_str(), std::ios_base::out); });
        auto get_object_outcome = client.GetObject(request);

        if (get_object_outcome.IsSuccess())
        {
            auto& result_stream = get_object_outcome.GetResult().GetBody();
            auto result = uncompressed_string_from_stream(result_stream);
            json_result = json::parse(result);
        }
        else
        {
            clog << "GetObject error: " <<
                get_object_outcome.GetError().GetExceptionName() << " " <<
                get_object_outcome.GetError().GetMessage() << std::endl;
        }
    }
    ShutdownAPI(options);

    return json_result;
}

Use following in CMakeLists.txt:

cmake_minimum_required(VERSION 3.5)
project(projname)
find_package(AWSSDK REQUIRED COMPONENTS s3)
find_package( ZLIB REQUIRED )
set(CMAKE_CXX_STANDARD 17)
add_executable(projname "projname.cpp")
# list all deps for static linking
target_link_libraries(projname ${AWSSDK_LINK_LIBRARIES} ${ZLIB_LIBRARIES})
target_compile_options(projname PRIVATE "-Wall" "-Werror")