Add better example for Connected

tonic/src/transport/server/conn.rs

@@ -15,7 +15,38 @@ use tokio_rustls::{rustls::Session, server::TlsStream};
 /// custom IO types that can still provide the same connection
 /// metadata.
 ///
-/// The `ConnectInfo` returned will be accessible through [request extensions][ext].
+/// # Example
+///
+/// The `ConnectInfo` returned will be accessible through [request extensions][ext]:
+///
+/// ```
+/// use tonic::{Request, transport::server::Connected};
+///
+/// // A `Stream` that yields connections
+/// struct MyConnector {}
+///
+/// // Return metadata about the connection as `MyConnectInfo`
+/// impl Connected for MyConnector {
+///     type ConnectInfo = MyConnectInfo;
+///
+///     fn connect_info(&self) -> Self::ConnectInfo {
+///         MyConnectInfo {}
+///     }
+/// }
+///
+/// #[derive(Clone)]
+/// struct MyConnectInfo {
+///     // Metadata about your connection
+/// }
+///
+/// // The connect info can be accessed through request extensions:
+/// # fn foo(request: Request<()>) {
+/// let connect_info: &MyConnectInfo = request
+///     .extensions()
+///     .get::<MyConnectInfo>()
+///     .expect("bug in tonic");
+/// # }
+/// ```
 ///
 /// [ext]: crate::Request::extensions
 pub trait Connected {