[DRAFT] update tokio-rustls to rustls 0.20.x

[hawkw]

This branch updates tokio-rustls to depend on the upcoming rustls
0.20.0 release (currently via a git dependency). Of course, since the
upstream breaking changes have yet to be released, this will remain a
draft PR until they are published.

I'm currently working on testing out Linkerd with the new API changes in
rustls 0.20.x (linkerd/linkerd2#6379). As we depend on both rustls
and tokio-rustls, this testing requires a version of tokio-rustls
using the upcoming rustls. I thought I'd go ahead and open a draft PR
for this change, since it may be useful for others who wish to test out
the upcoming rustls as well. When rustls v0.20.0 is published, we
can mark this PR as "ready for review" and move forwards with it, but
it'll remain a draft until then.

[hawkw]

Trying to figure out what's up with the test failure we're seeing here --- it's possible some behavior changed in rustls, because this is actually quite surprising.

[quininer]

Good job! I have a branch that does the same thing, but it's a bit behind.

I am not surprised that some tests failed, because I noticed some behavioral changes in rustls 0.20, but it should be easy to fix.

[djc]

There were some changes to the reader behavior and how it signals EOF and errors. I think this upstream commit contains the meat of the relevant changes:

rustls/rustls@c94c223

[djc]

(I have a PR against rustls-native-certs that removes the dependency on rustls, might also be useful when testing.)

[hawkw]

Good job! I have a branch that does the same thing, but it's a bit behind.

Oh, whoops --- I looked at the open PRs, but not at all open branches. Hope I didn't step on your toes here, I just wanted to get a version compiling with 0.20 so we can test our code downstream.

There were some changes to the reader behavior and how it signals EOF and errors. I think this upstream commit contains the meat of the relevant changes:

ctz/rustls@c94c223

Great, thanks for the commit, that's very helpful :)

[quininer]

This has been reviewed in #68, so I will merge it now.

[Stargateur]

Since this get merge, readme link are broken https://github.com/tokio-rs/tls/blob/HEAD/examples/server/src/main.rs; and so I go to the repo directly and end up with:

error[E0277]: the trait bound `tokio_rustls::TlsAcceptor: From<Arc<rustls::ServerConfig>>` is not satisfied
   --> src\main.rs:184:24
    |
184 |         let acceptor = TlsAcceptor::from(Arc::new(config));
    |                        ^^^^^^^^^^^^^^^^^ the trait `From<Arc<rustls::ServerConfig>>` is not implemented for `tokio_rustls::TlsAcceptor`
    |
    = help: the following implementations were found:
              <tokio_rustls::TlsAcceptor as From<Arc<tokio_rustls::rustls::ServerConfig>>>
note: required by `std::convert::From::from`
   --> C:\Users\Star\.rustup\toolchains\stable-x86_64-pc-windows-msvc\lib/rustlib/src/rust\library\core\src\convert\mod.rs:371:5
    |
371 |     fn from(_: T) -> Self;
    |     ^^^^^^^^^^^^^^^^^^^^^^

would be nice to make a release soon and use permalink in the readme.