Supports:

• tokio and async-std
• rustls, native-tls, openssl, security-framework

• tls-api — TLS API without any implementation and without dependencies
• tls-api-native-tls — implementation of TLS API over native-tls crate
• tls-api-openssl — implementation of TLS API over openssl crate
• tls-api-rustls — implementation of TLS API over rustls crate
• tls-api-security-framework — implementation of TLS API over security framework crate
• tls-api-schannel — missing implementation of TLS API over schannel crate
• tls-api-stub — stub API implementation which returns an error on any operation
• tls-api-not-tls — stub API implementation which pretends to be TLS, but returns wrapped plain socket
• test-cert-gen — utility to generate certificate for unit tests

• it is not decided yet which TLS implementation is better, start prototyping with one, and then switch to another
• something doesn't work, no idea why, maybe try another implementation which would provide better diagnostics
• provide a library over TLS (like database client) and allow user do specify preferred TLS implementation
• do a performace comparison of TLS implementations on the same code base
• if one implementation is buggy, it's easy to switch to another without heavy rewrite

download-rust-lang-org.rs contains the implementation of simple TLS client downloading rust-lang.org, which is invoked with four backends.

• does not support server side ALPN
• requires PKCS #12 keys on the server side
• building OpenSSL on Linux is not always trivial

• sometimes it's hard to compile it
• some concerns about OpenSSL safety

• diagnostics of rustls is not perfect
• certain TLS features are not supported

• only works on Apple
• does not support server side ALPN