Add cargo features "client" and "server"

Since many consumers of this library do not need both client and server
features, this allows them to shrink their dependencies somewhat.

Cargo.toml

@@ -18,13 +18,24 @@ appveyor = { repository = "async-std/async-tls" }
 [dependencies]
 futures = "0.3.4"
 rustls = "0.17.0"
-webpki = "0.21.2"
-webpki-roots = "0.19.0"
+webpki = { version = "0.21.2", optional = true }
+webpki-roots = { version = "0.19.0", optional = true }
 
 [features]
+default = ["client", "server"]
+client = ["webpki", "webpki-roots"]
 early-data = []
+server = []
 
 [dev-dependencies]
 lazy_static = "1"
 futures-util = "0.3"
 async-std = { version = "1.0", features = ["unstable"] }
+
+[[test]]
+name = "test"
+required-features = ["client", "server"]
+
+[[test]]
+name = "google"
+required-features = ["client"]

src/lib.rs

@@ -2,16 +2,21 @@
 
 #![deny(unsafe_code)]
 
+#[cfg(feature = "server")]
 mod acceptor;
+#[cfg(feature = "client")]
 pub mod client;
 mod common;
+#[cfg(feature = "client")]
 mod connector;
 mod rusttls;
+#[cfg(feature = "server")]
 pub mod server;
 
+#[cfg(feature = "server")]
 pub use acceptor::{Accept, TlsAcceptor};
+#[cfg(feature = "client")]
 pub use connector::{Connect, TlsConnector};
 
-#[cfg(feature = "early-data")]
-#[cfg(test)]
+#[cfg(all(test, feature = "client", feature = "early-data"))]
 mod test_0rtt;

src/rusttls/stream.rs

@@ -257,6 +257,6 @@ impl<'a, IO: AsyncRead + AsyncWrite + Unpin, S: Session> AsyncWrite for Stream<'
     }
 }
 
-#[cfg(test)]
+#[cfg(all(test, feature = "client"))]
 #[path = "test_stream.rs"]
 mod test_stream;