hyperium · LucioFranco · Jul 10, 2020 · Feb 28, 2020 · Jun 26, 2020 · Jul 10, 2020
diff --git a/examples/Cargo.toml b/examples/Cargo.toml
@@ -122,6 +122,10 @@ path = "src/health/server.rs"
 name = "autoreload-server"
 path = "src/autoreload/server.rs"
 
+[[bin]]
+name = "optional-server"
+path = "src/optional/server.rs"
+
 [dependencies]
 tonic = { path = "../tonic", features = ["tls"] }
 prost = "0.6"

diff --git a/examples/src/optional/server.rs b/examples/src/optional/server.rs
@@ -0,0 +1,53 @@
+use std::env;
+use tonic::{transport::Server, Request, Response, Status};
+
+use hello_world::greeter_server::{Greeter, GreeterServer};
+use hello_world::{HelloReply, HelloRequest};
+
+pub mod hello_world {
+    tonic::include_proto!("helloworld");
+}
+
+#[derive(Default)]
+pub struct MyGreeter {}
+
+#[tonic::async_trait]
+impl Greeter for MyGreeter {
+    async fn say_hello(
+        &self,
+        request: Request<HelloRequest>,
+    ) -> Result<Response<HelloReply>, Status> {
+        println!("Got a request from {:?}", request.remote_addr());
+
+        let reply = hello_world::HelloReply {
+            message: format!("Hello {}!", request.into_inner().name),
+        };
+        Ok(Response::new(reply))
+    }
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let args: Vec<String> = env::args().collect();
+    let enabled = args.get(1) == Some(&"enable".to_string());
+
+    let addr = "[::1]:50051".parse().unwrap();
+    let greeter = MyGreeter::default();
+
+    let optional_service = if enabled {
+        println!("MyGreeter enabled");
+        Some(GreeterServer::new(greeter))
+    } else {
+        println!("MyGreeter disabled");
+        None
+    };
+
+    println!("GreeterServer listening on {}", addr);
+
+    Server::builder()
+        .add_optional_service(optional_service)
+        .serve(addr)
+        .await?;
+
+    Ok(())
+}
diff --git a/tonic/src/transport/server/mod.rs b/tonic/src/transport/server/mod.rs
@@ -41,7 +41,8 @@ use std::{
 };
 use tokio::io::{AsyncRead, AsyncWrite};
 use tower::{
-    limit::concurrency::ConcurrencyLimitLayer, timeout::TimeoutLayer, Service, ServiceBuilder,
+    limit::concurrency::ConcurrencyLimitLayer, timeout::TimeoutLayer, util::Either, Service,
+    ServiceBuilder,
 };
 use tracing_futures::{Instrument, Instrumented};
 
@@ -86,6 +87,10 @@ pub trait NamedService {
     const NAME: &'static str;
 }
 
+impl<S: NamedService, T> NamedService for Either<S, T> {
+    const NAME: &'static str = S::NAME;
+}
+
 impl Server {
     /// Create a new server builder that can configure a [`Server`].
     pub fn builder() -> Self {
@@ -231,6 +236,34 @@ impl Server {
         Router::new(self.clone(), svc)
     }
 
+    /// Create a router with the optional `S` typed service as the first service.
+    ///
+    /// This will clone the `Server` builder and create a router that will
+    /// route around different services.
+    ///
+    /// # Note
+    /// Even when the argument given is `None` this will capture *all* requests to this service name.
+    /// As a result, one cannot use this to toggle between two indentically named implementations.
+    pub fn add_optional_service<S>(
+        &mut self,
+        svc: Option<S>,
+    ) -> Router<Either<S, Unimplemented>, Unimplemented>
+    where
+        S: Service<Request<Body>, Response = Response<BoxBody>>
+            + NamedService
+            + Clone
+            + Send
+            + 'static,
+        S::Future: Send + 'static,
+        S::Error: Into<crate::Error> + Send,
+    {
+        let svc = match svc {
+            Some(some) => Either::A(some),
+            None => Either::B(Unimplemented::default()),
+        };
+        Router::new(self.clone(), svc)
+    }
+
     pub(crate) async fn serve_with_shutdown<S, I, F, IO, IE>(
         self,
         svc: S,
@@ -342,6 +375,42 @@ where
         Router { server, routes }
     }
 
+    /// Add a new optional service to this router.
+    ///
+    /// # Note
+    /// Even when the argument given is `None` this will capture *all* requests to this service name.
+    /// As a result, one cannot use this to toggle between two indentically named implementations.
+    pub fn add_optional_service<S>(
+        self,
+        svc: Option<S>,
+    ) -> Router<Either<S, Unimplemented>, Or<A, B, Request<Body>>>
+    where
+        S: Service<Request<Body>, Response = Response<BoxBody>>
+            + NamedService
+            + Clone
+            + Send
+            + 'static,
+        S::Future: Send + 'static,
+        S::Error: Into<crate::Error> + Send,
+    {
+        let Self { routes, server } = self;
+
+        let svc_name = <S as NamedService>::NAME;
+        let svc_route = format!("/{}", svc_name);
+        let pred = move |req: &Request<Body>| {
+            let path = req.uri().path();
+
+            path.starts_with(&svc_route)
+        };
+        let svc = match svc {
+            Some(some) => Either::A(some),
+            None => Either::B(Unimplemented::default()),
+        };
+        let routes = routes.push(pred, svc);
+
+        Router { server, routes }
+    }
+
     /// Consume this [`Server`] creating a future that will execute the server
     /// on [`tokio`]'s default executor.
     ///