feat: add GrpcMethod extension into request for client (#1275)

* feat: add GrpcMethod extension into request for client

* refactor: change GrpcMethod fields into private and expose methods instead

* refactor: hide GrpcMethod::new in doc

---------

Co-authored-by: Lucio Franco <luciofranco14@gmail.com>

tests/integration_tests/tests/interceptor.rs

@@ -0,0 +1,53 @@
+use std::time::Duration;
+
+use futures::{channel::oneshot, FutureExt};
+use integration_tests::pb::{test_client::TestClient, test_server, Input, Output};
+use tonic::{
+    transport::{Endpoint, Server},
+    GrpcMethod, Request, Response, Status,
+};
+
+#[tokio::test]
+async fn interceptor_retrieves_grpc_method() {
+    use test_server::Test;
+
+    struct Svc;
+
+    #[tonic::async_trait]
+    impl Test for Svc {
+        async fn unary_call(&self, _: Request<Input>) -> Result<Response<Output>, Status> {
+            Ok(Response::new(Output {}))
+        }
+    }
+
+    let svc = test_server::TestServer::new(Svc);
+
+    let (tx, rx) = oneshot::channel();
+    // Start the server now, second call should succeed
+    let jh = tokio::spawn(async move {
+        Server::builder()
+            .add_service(svc)
+            .serve_with_shutdown("127.0.0.1:1340".parse().unwrap(), rx.map(drop))
+            .await
+            .unwrap();
+    });
+
+    let channel = Endpoint::from_static("http://127.0.0.1:1340").connect_lazy();
+
+    fn client_intercept(req: Request<()>) -> Result<Request<()>, Status> {
+        println!("Intercepting client request: {:?}", req);
+
+        let gm = req.extensions().get::<GrpcMethod>().unwrap();
+        assert_eq!(gm.service(), "test.Test");
+        assert_eq!(gm.method(), "UnaryCall");
+
+        Ok(req)
+    }
+    let mut client = TestClient::with_interceptor(channel, client_intercept);
+
+    tokio::time::sleep(Duration::from_millis(100)).await;
+    client.unary_call(Request::new(Input {})).await.unwrap();
+
+    tx.send(()).unwrap();
+    jh.await.unwrap();
+}