doc(tokio): Set keep_alive to false on hyper clients.

This prevents hanging event loops.

examples/test-device/src/main.rs

@@ -11,8 +11,9 @@ fn main() {
     let creds = yup_oauth2::read_application_secret(path::Path::new("clientsecret.json"))
         .expect("clientsecret");
     let https = HttpsConnector::new(1).expect("tls");
-    let client = Client::builder().build::<_, hyper::Body>(https);
-
+    let client = Client::builder()
+        .keep_alive(false)
+        .build::<_, hyper::Body>(https);
     let scopes = &["https://www.googleapis.com/auth/youtube.readonly".to_string()];
 
     let ad = yup_oauth2::DefaultFlowDelegate;

examples/test-installed/src/main.rs

@@ -9,7 +9,9 @@ use std::path::Path;
 
 fn main() {
     let https = HttpsConnector::new(1).expect("tls");
-    let client = Client::builder().build::<_, hyper::Body>(https);
+    let client = Client::builder()
+        .keep_alive(false)
+        .build::<_, hyper::Body>(https);
     let ad = yup_oauth2::DefaultFlowDelegate;
     let secret = yup_oauth2::read_application_secret(Path::new("clientsecret.json"))
         .expect("clientsecret.json");
@@ -35,6 +37,5 @@ fn main() {
         Ok(())
     });
 
-    let mut rt = tokio::runtime::Runtime::new().unwrap();
-    rt.block_on(fut).unwrap();
+    tokio::run(fut)
 }

examples/test-svc-acct/src/main.rs

@@ -13,7 +13,9 @@ fn main() {
     let creds =
         yup_oauth2::service_account_key_from_file(path::Path::new("serviceaccount.json")).unwrap();
     let https = HttpsConnector::new(1).expect("tls");
-    let client = Client::builder().build::<_, hyper::Body>(https);
+    let client = Client::builder()
+        .keep_alive(false)
+        .build::<_, hyper::Body>(https);
 
     let mut sa = yup_oauth2::ServiceAccountAccess::new(creds, client);
 
@@ -29,7 +31,6 @@ fn main() {
             println!("cached token is {:?} and should be identical", tok);
             Ok(())
         });
-    let all = fut.join(fut2);
-    let mut rt = tokio::runtime::Runtime::new().unwrap();
-    rt.block_on(all).unwrap();
+    let all = fut.join(fut2).then(|_| Ok(()));
+    tokio::run(all)
 }

src/authenticator.rs

@@ -16,6 +16,10 @@ use std::sync::{Arc, Mutex};
 ///
 /// `ServiceAccountAccess` does not need (and does not work) with `Authenticator`, given that it
 /// does not require interaction and implements its own caching. Use it directly.
+///
+/// NOTE: It is recommended to use a client constructed like this in order to prevent functions
+/// like `hyper::run()` from hanging: `let client = hyper::Client::builder().keep_alive(false);`.
+/// Due to token requests being rare, this should not result in a too bad performance problem.
 pub struct Authenticator<
     T: GetToken,
     S: TokenStorage,