In this particular case, the Tokio based implementation of streaming files up and down AWS S3 from crate rust-s3 is bound to a C++ Boost::ASIO app (find this in directory test/asio). The app can be tested with AWS S3 directly or with emulators like Localstack.
Show HN: A practical example of using async Rust runtimes in C and C++ | Heykuki News