Created async request-reply for Tari p2p services

This PR contains the building blocks for async p2p services.

It consists of the following modules:
- `builder`: contains the `MakeServicePair` trait which should be implemented by a service builder and the
`StackBuilder` struct which is responsible for building the service and making service _handles_ available to all
the other services. Handles are any object which is able to control a service in some way. Most commonly the
handle will be a `transport::Requester<MyServiceRequest>`.
- `handles`: struct for collecting named handles for services. The `StackBuilder` uses this to make all handles
available to services.
- `transport`: This allows messages to be reliably send/received to/from services. A `Requester`/`Responder` pair is
created using the `transport::channel` function which takes an impl of `tower_service::Service` as it's first
parameter. A `Requester` implements `tower_service::Service` and is used to send requests which return a Future
which resolves to a response. The `Requester` uses a `oneshot` channel allow responses to be sent back. A
`Responder` receives a `(request, oneshot::Sender)` tuple, calls the given tower service with that request and
sends the result on the `oneshot::Sender`. The `Responder` handles many requests simultaneously.

base_layer/p2p/Cargo.toml

@@ -22,6 +22,7 @@ chrono = { version = "0.4.6", features = ["serde"]}
 tokio = "0.1.22"
 futures = "0.1.28"
 tower-service = "0.2.0"
+tower-util = "0.1.0"
 ttl_cache = "0.5.1"
 
 [dev-dependencies]

base_layer/p2p/src/executor/builder.rs

@@ -0,0 +1,129 @@
+// Copyright 2019 The Tari Project
+//
+// Redistribution and use in source and binary forms, with or without modification, are permitted provided that the
+// following conditions are met:
+//
+// 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following
+// disclaimer.
+//
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the
+// following disclaimer in the documentation and/or other materials provided with the distribution.
+//
+// 3. Neither the name of the copyright holder nor the names of its contributors may be used to endorse or promote
+// products derived from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
+// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
+// WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+// USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+use crate::executor::handles::ServiceHandles;
+use futures::{future, Future, IntoFuture};
+use std::{any::Any, hash::Hash, sync::Arc};
+
+/// Builder trait for creating a service/handle pair.
+/// The `StackBuilder` builds impls of this trait.
+pub trait MakeServicePair<N> {
+    type Future: Future<Item = (), Error = ()> + Send;
+    type Handle: Any + Send + Sync;
+
+    fn make_pair(self, handles: Arc<ServiceHandles<N>>) -> (Self::Handle, Self::Future);
+}
+
+impl<FN, F, H, N> MakeServicePair<N> for FN
+where
+    FN: FnOnce(Arc<ServiceHandles<N>>) -> (H, F),
+    F: Future<Item = (), Error = ()> + Send,
+    H: Any,
+    H: Send + Sync,
+    N: Eq + Hash,
+{
+    type Future = F;
+    type Handle = H;
+
+    fn make_pair(self, handles: Arc<ServiceHandles<N>>) -> (Self::Handle, Self::Future) {
+        (self)(handles)
+    }
+}
+
+/// Responsible for building and collecting handles and (usually long-running) service futures.
+/// This can be converted into a future which resolves once all contained service futures are complete
+/// by using the `IntoFuture` implementation.
+pub struct StackBuilder<N> {
+    handles: Arc<ServiceHandles<N>>,
+    futures: Vec<Box<dyn Future<Item = (), Error = ()> + Send>>,
+}
+
+impl<N> StackBuilder<N>
+where
+    N: Eq + Hash,
+    N: Send + Sync + 'static,
+{
+    pub fn new() -> Self {
+        let handles = Arc::new(ServiceHandles::new());
+        Self {
+            handles,
+            futures: Vec::new(),
+        }
+    }
+
+    pub fn add_service(mut self, name: N, maker: impl MakeServicePair<N> + Send + 'static) -> Self {
+        let (handle, fut) = maker.make_pair(self.handles.clone());
+        self.handles.insert(name, handle);
+        self.futures.push(Box::new(fut));
+        self
+    }
+}
+
+impl<N> IntoFuture for StackBuilder<N> {
+    type Error = ();
+    type Item = ();
+
+    existential type Future: Future<Item = (), Error = ()> + Send;
+
+    fn into_future(self) -> Self::Future {
+        future::join_all(self.futures).map(|_| ())
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use futures::{future::poll_fn, Async};
+    use std::sync::atomic::{AtomicBool, Ordering};
+
+    #[test]
+    fn service_stack_new() {
+        let state = Arc::new(AtomicBool::new(false));
+        let state_inner = Arc::clone(&state.clone());
+        let service_pair_factory = |handles: Arc<ServiceHandles<&'static str>>| {
+            let fut = poll_fn(move || {
+                // Test that this futures own handle is available
+                let fake_handle = handles.get_handle::<&str>(&"test-service").unwrap();
+                assert_eq!(fake_handle, "Fake Handle");
+                let not_found = handles.get_handle::<&str>(&"not-found");
+                assert!(not_found.is_none());
+
+                // Any panics above won't fail the test so a marker bool is set
+                // if there are no panics.
+                // catch_unwind could be used but then the UnwindSafe trait bound
+                // needs to be added. TODO: handle panics in service poll functions
+                state_inner.store(true, Ordering::Release);
+                Ok(Async::Ready(()))
+            });
+
+            ("Fake Handle", fut)
+        };
+
+        tokio::run(
+            StackBuilder::new()
+                .add_service("test-service", service_pair_factory)
+                .into_future(),
+        );
+
+        assert!(state.load(Ordering::Acquire))
+    }
+}