Optionally disable pulling in the tokio runtime

Before this patch, hyper-rustls required pulling in the tokio runtime
due to it's use of `hyper::client::HttpConnector`. Unfortunately
Fuchsia does not support tokio, which prevents our use of this
library. This PR allows us to optionally disable pulling in tokio,
and instead swap in our own version of the hyper `HttpConnector`.

Author: erickt

Cargo.toml

@@ -10,15 +10,19 @@ repository = "https://github.com/ctz/hyper-rustls"
 
 [dependencies]
 bytes = "0.4"
-ct-logs = "0.5"
+ct-logs = { version = "0.5", optional = true }
 futures = "0.1.21"
-hyper = "0.12.14"
+hyper = { version = "0.12.14", default-features = false }
 rustls = "0.15"
 tokio-io = "0.1.1"
 tokio-rustls = "0.9"
 webpki = "0.19.0"
-webpki-roots = "0.16"
+webpki-roots = { version = "0.16", optional = true }
 
 [dev-dependencies]
 tokio = "0.1"
 tokio-tcp = "0.1"
+
+[features]
+default = ["tokio-runtime"]
+tokio-runtime = ["hyper/runtime", "ct-logs", "webpki-roots"]

src/connector.rs

@@ -1,13 +1,12 @@
-use ct_logs;
 use futures::{Future, Poll};
 use hyper::client::connect::{self, Connect};
+#[cfg(feature = "tokio-runtime")]
 use hyper::client::HttpConnector;
 use rustls::{ClientConfig, Session};
 use std::sync::Arc;
 use std::{fmt, io};
 use tokio_rustls::TlsConnector;
 use webpki::{DNSName, DNSNameRef};
-use webpki_roots;
 
 use stream::MaybeHttpsStream;
 
@@ -18,11 +17,15 @@ pub struct HttpsConnector<T> {
     tls_config: Arc<ClientConfig>,
 }
 
+#[cfg(feature = "tokio-runtime")]
 impl HttpsConnector<HttpConnector> {
     /// Construct a new `HttpsConnector`.
     ///
     /// Takes number of DNS worker threads.
     pub fn new(threads: usize) -> Self {
+        use ct_logs;
+        use webpki_roots;
+
         let mut http = HttpConnector::new(threads);
         http.enforce_http(false);
         let mut config = ClientConfig::new();

src/lib.rs

@@ -24,13 +24,15 @@
 //! ```
 
 extern crate bytes;
+#[cfg(feature = "tokio-runtime")]
 extern crate ct_logs;
 extern crate futures;
 extern crate hyper;
 extern crate rustls;
 extern crate tokio_io;
 extern crate tokio_rustls;
 extern crate webpki;
+#[cfg(feature = "tokio-runtime")]
 extern crate webpki_roots;
 
 mod connector;