feat(service): add poll_ready to Service and MakeService (#1767)

src/proto/h1/dispatch.rs

@@ -189,7 +189,7 @@ where
         // can dispatch receive, or does it still care about, an incoming message?
         match self.dispatch.poll_ready() {
             Ok(Async::Ready(())) => (),
-            Ok(Async::NotReady) => unreachable!("dispatch not ready when conn is"),
+            Ok(Async::NotReady) => return Ok(Async::NotReady), // service might not be ready
             Err(()) => {
                 trace!("dispatch no longer receiving messages");
                 self.close();
@@ -410,7 +410,11 @@ where
         if self.in_flight.is_some() {
             Ok(Async::NotReady)
         } else {
-            Ok(Async::Ready(()))
+            self.service.poll_ready()
+                .map_err(|_e| {
+                    // FIXME: return error value.
+                    trace!("service closed");
+                })
         }
     }
 

src/proto/h2/server.rs

@@ -128,19 +128,37 @@ where
         S::Error: Into<Box<::std::error::Error + Send + Sync>>,
         E: H2Exec<S::Future, B>,
     {
-        while let Some((req, respond)) = try_ready!(self.conn.poll().map_err(::Error::new_h2)) {
-            trace!("incoming request");
-            let content_length = content_length_parse_all(req.headers());
-            let req = req.map(|stream| {
-                ::Body::h2(stream, content_length)
-            });
-            let fut = H2Stream::new(service.call(req), respond);
-            exec.execute_h2stream(fut)?;
-        }
+        loop {
+            // At first, polls the readiness of supplied service.
+            match service.poll_ready() {
+                Ok(Async::Ready(())) => (),
+                Ok(Async::NotReady) => {
+                    // use `poll_close` instead of `poll`, in order to avoid accepting a request.
+                    try_ready!(self.conn.poll_close().map_err(::Error::new_h2));
+                    trace!("incoming connection complete");
+                    return Ok(Async::Ready(()));
+                }
+                Err(err) => {
+                    trace!("service closed");
+                    return Err(::Error::new_user_service(err));
+                }
+            }
 
-        // no more incoming streams...
-        trace!("incoming connection complete");
-        Ok(Async::Ready(()))
+            // When the service is ready, accepts an incoming request.
+            if let Some((req, respond)) = try_ready!(self.conn.poll().map_err(::Error::new_h2)) {
+                trace!("incoming request");
+                let content_length = content_length_parse_all(req.headers());
+                let req = req.map(|stream| {
+                    ::Body::h2(stream, content_length)
+                });
+                let fut = H2Stream::new(service.call(req), respond);
+                exec.execute_h2stream(fut)?;
+            } else {
+                // no more incoming streams...
+                trace!("incoming connection complete");
+                return Ok(Async::Ready(()))
+            }
+        }
     }
 }
 

src/server/conn.rs

@@ -646,6 +646,15 @@ where
     type Error = ::Error;
 
     fn poll(&mut self) -> Poll<Option<Self::Item>, Self::Error> {
+        match self.make_service.poll_ready_ref() {
+            Ok(Async::Ready(())) => (),
+            Ok(Async::NotReady) => return Ok(Async::NotReady),
+            Err(e) => {
+                trace!("make_service closed");
+                return Err(::Error::new_user_new_service(e));
+            }
+        }
+
         if let Some(io) = try_ready!(self.incoming.poll().map_err(::Error::new_accept)) {
             let new_fut = self.make_service.make_service_ref(&io);
             Ok(Async::Ready(Some(Connecting {

src/service/make_service.rs

@@ -1,7 +1,7 @@
 use std::error::Error as StdError;
 use std::fmt;
 
-use futures::{Future, IntoFuture};
+use futures::{Async, Future, IntoFuture, Poll};
 
 use body::Payload;
 use super::Service;
@@ -30,6 +30,15 @@ pub trait MakeService<Ctx> {
     /// The error type that can be returned when creating a new `Service`.
     type MakeError: Into<Box<StdError + Send + Sync>>;
 
+    /// Returns `Ready` when the constructor is ready to create a new `Service`.
+    ///
+    /// The implementation of this method is allowed to return a `Ready` even if
+    /// the factory is not ready to create a new service. In this case, the future
+    /// returned from `make_service` will resolve to an error.
+    fn poll_ready(&mut self) -> Poll<(), Self::MakeError> {
+        Ok(Async::Ready(()))
+    }
+
     /// Create a new `Service`.
     fn make_service(&mut self, ctx: Ctx) -> Self::Future;
 }
@@ -46,7 +55,8 @@ pub trait MakeServiceRef<Ctx>: self::sealed::Sealed<Ctx> {
         ResBody=Self::ResBody,
         Error=Self::Error,
     >;
-    type Future: Future<Item=Self::Service>;
+    type MakeError: Into<Box<StdError + Send + Sync>>;
+    type Future: Future<Item=Self::Service, Error=Self::MakeError>;
 
     // Acting like a #[non_exhaustive] for associated types of this trait.
     //
@@ -59,6 +69,8 @@ pub trait MakeServiceRef<Ctx>: self::sealed::Sealed<Ctx> {
     // if necessary.
     type __DontNameMe: self::sealed::CantImpl;
 
+    fn poll_ready_ref(&mut self) -> Poll<(), Self::MakeError>;
+
     fn make_service_ref(&mut self, ctx: &Ctx) -> Self::Future;
 }
 
@@ -76,10 +88,15 @@ where
     type Service = S;
     type ReqBody = IB;
     type ResBody = OB;
+    type MakeError = ME;
     type Future = F;
 
     type __DontNameMe = self::sealed::CantName;
 
+    fn poll_ready_ref(&mut self) -> Poll<(), Self::MakeError> {
+        self.poll_ready()
+    }
+
     fn make_service_ref(&mut self, ctx: &Ctx) -> Self::Future {
         self.make_service(ctx)
     }

src/service/new_service.rs

@@ -1,6 +1,6 @@
 use std::error::Error as StdError;
 
-use futures::{Future, IntoFuture};
+use futures::{Async, Future, IntoFuture, Poll};
 
 use body::Payload;
 use super::{MakeService, Service};
@@ -29,6 +29,11 @@ pub trait NewService {
     /// The error type that can be returned when creating a new `Service`.
     type InitError: Into<Box<StdError + Send + Sync>>;
 
+    #[doc(hidden)]
+    fn poll_ready(&mut self) -> Poll<(), Self::InitError> {
+        Ok(Async::Ready(()))
+    }
+
     /// Create a new `Service`.
     fn new_service(&self) -> Self::Future;
 }
@@ -63,6 +68,10 @@ where
     type Future = N::Future;
     type MakeError = N::InitError;
 
+    fn poll_ready(&mut self) -> Poll<(), Self::MakeError> {
+        NewService::poll_ready(self)
+    }
+
     fn make_service(&mut self, _: Ctx) -> Self::Future {
         self.new_service()
     }

src/service/service.rs

@@ -2,7 +2,7 @@ use std::error::Error as StdError;
 use std::fmt;
 use std::marker::PhantomData;
 
-use futures::{future, Future, IntoFuture};
+use futures::{future, Async, Future, IntoFuture, Poll};
 
 use body::Payload;
 use common::Never;
@@ -26,6 +26,15 @@ pub trait Service {
     /// The `Future` returned by this `Service`.
     type Future: Future<Item=Response<Self::ResBody>, Error=Self::Error>;
 
+    /// Returns `Ready` when the service is able to process requests.
+    ///
+    /// The implementation of this method is allowed to return a `Ready` even if
+    /// the service is not ready to process. In this case, the future returned
+    /// from `call` will resolve to an error.
+    fn poll_ready(&mut self) -> Poll<(), Self::Error> {
+        Ok(Async::Ready(()))
+    }
+
     /// Calls this `Service` with a request, returning a `Future` of the response.
     fn call(&mut self, req: Request<Self::ReqBody>) -> Self::Future;
 }