Upcoming Rustls support

[sagebind]

For a long time, the ability to use Rustls as a TLS backend for HTTPS requests has been a common and hightly anticipated feature request. Well I am finally able to share some good news on this: We now have a fully-working branch with Rustls support! You can try it out today by using the rustls branch from our Git repository:

$ git checkout rustls
$ cargo run --example version --features unstable-rustls-tls
version: isahc/1.6.0 (features:default,encoding_rs,http2,mime,static_curl,text_decoding,unstable_rustls_tls) libcurl/7.80.1-DEV rustls-ffi/0.8.2/rustls/0.20.0 zlib/1.2.11 nghttp2/1.45.0

This has been made possible by the work done on rustls-ffi to expose a C interface for Rustls which curl can use under the hood for TLS support. We expect curl 7.81.0 to be released with full support of the current version of rustls-ffi in early January 2022, at which point we can merge in Rustls support when using the latest bundled curl version.

When released, the plan is that Rustls will be opt-in with the unstable-rustls-tls feature flag, as Rustls support in curl does have a few known bugs for now and we can't guarantee full feature parity yet. Once those are ironed out the feature flag will be renamed appropriately.

Learn more about the Rustls backend on our new wiki page here: https://github.com/sagebind/isahc/wiki/TLS-Backends#rustls. Also you can watch this issue for updates: #199