light-client: turn Handle into a trait

CHANGES.md

@@ -3,6 +3,10 @@
 Light Client:
 
 - Expose latest_trusted from Supervisor Handle ([#394])
+- Turn `Handle` into a trait for ease of integration and testability ([#401])
+
+[#394]: https://github.com/informalsystems/tendermint-rs/pull/394
+[#401]: https://github.com/informalsystems/tendermint-rs/pull/401
 
 ## [0.14.1] (2020-06-23)
 

light-client/examples/light_client.rs

@@ -1,3 +1,12 @@
+use std::collections::HashMap;
+use std::{
+    path::{Path, PathBuf},
+    time::Duration,
+};
+
+use gumdrop::Options;
+
+use tendermint_light_client::supervisor::{Handle as _, Instance, Supervisor};
 use tendermint_light_client::{
     components::{
         clock::SystemClock,
@@ -11,18 +20,9 @@ use tendermint_light_client::{
     peer_list::PeerList,
     state::State,
     store::{sled::SledStore, LightStore},
-    supervisor::{Instance, Supervisor},
     types::{Height, PeerId, Status, Time, TrustThreshold},
 };
 
-use gumdrop::Options;
-
-use std::collections::HashMap;
-use std::{
-    path::{Path, PathBuf},
-    time::Duration,
-};
-
 #[derive(Debug, Options)]
 struct CliOptions {
     #[options(help = "print this help message")]

light-client/src/supervisor.rs

@@ -15,6 +15,39 @@ use crate::{
     types::{Height, LightBlock, PeerId, Status},
 };
 
+pub trait Handle {
+    /// Get latest trusted block from the [`Supervisor`].
+    fn latest_trusted(&mut self) -> Result<Option<LightBlock>, Error>;
+
+    /// Verify to the highest block.
+    fn verify_to_highest(&mut self) -> Result<LightBlock, Error>;
+
+    /// Verify to the block at the given height.
+    fn verify_to_target(&mut self, height: Height) -> Result<LightBlock, Error>;
+
+    /// Async version of `verify_to_highest`.
+    ///
+    /// The given `callback` will be called asynchronously with the
+    /// verification result.
+    fn verify_to_highest_async(
+        &mut self,
+        callback: impl FnOnce(Result<LightBlock, Error>) -> () + Send + 'static,
+    );
+
+    /// Async version of `verify_to_target`.
+    ///
+    /// The given `callback` will be called asynchronously with the
+    /// verification result.
+    fn verify_to_target_async(
+        &mut self,
+        height: Height,
+        callback: impl FnOnce(Result<LightBlock, Error>) -> () + Send + 'static,
+    );
+
+    /// Terminate the underlying [`Supervisor`].
+    fn terminate(&mut self);
+}
+
 /// Input events sent by the [`Handle`]s to the [`Supervisor`]. They carry a [`Callback`] which is
 /// used to communicate back the responses of the requests.
 #[derive(Debug)]
@@ -134,8 +167,8 @@ impl Supervisor {
     }
 
     /// Create a new handle to this supervisor.
-    pub fn handle(&mut self) -> Handle {
-        Handle::new(self.sender.clone())
+    pub fn handle(&mut self) -> impl Handle {
+        SupervisorHandle::new(self.sender.clone())
     }
 
     #[pre(self.peers.primary().is_some())]
@@ -308,21 +341,38 @@ impl Supervisor {
     }
 }
 
-/// A handle to a `Supervisor` which allows to communicate with
+/// A [`Handle`] to the [`Supervisor`] which allows to communicate with
 /// the supervisor across thread boundaries via message passing.
-pub struct Handle {
+struct SupervisorHandle {
     sender: channel::Sender<HandleInput>,
 }
 
-impl Handle {
+impl SupervisorHandle {
     /// Crate a new handle that sends events to the supervisor via
     /// the given channel. For internal use only.
     fn new(sender: channel::Sender<HandleInput>) -> Self {
         Self { sender }
     }
 
-    /// Get latest trusted block from the [`Supervisor`].
-    pub fn latest_trusted(&mut self) -> Result<Option<LightBlock>, Error> {
+    fn verify(
+        &mut self,
+        make_event: impl FnOnce(Callback<Result<LightBlock, Error>>) -> HandleInput,
+    ) -> Result<LightBlock, Error> {
+        let (sender, receiver) = channel::bounded::<Result<LightBlock, Error>>(1);
+
+        let callback = Callback::new(move |result| {
+            sender.send(result).unwrap();
+        });
+
+        let event = make_event(callback);
+        self.sender.send(event).unwrap();
+
+        receiver.recv().unwrap()
+    }
+}
+
+impl Handle for SupervisorHandle {
+    fn latest_trusted(&mut self) -> Result<Option<LightBlock>, Error> {
         let (sender, receiver) = channel::bounded::<Result<Option<LightBlock>, Error>>(1);
 
         let callback = Callback::new(move |result| {
@@ -338,50 +388,23 @@ impl Handle {
         receiver.recv().unwrap()
     }
 
-    /// Verify to the highest block.
-    pub fn verify_to_highest(&mut self) -> Result<LightBlock, Error> {
+    fn verify_to_highest(&mut self) -> Result<LightBlock, Error> {
         self.verify(HandleInput::VerifyToHighest)
     }
 
-    /// Verify to the block at the given height.
-    pub fn verify_to_target(&mut self, height: Height) -> Result<LightBlock, Error> {
+    fn verify_to_target(&mut self, height: Height) -> Result<LightBlock, Error> {
         self.verify(|callback| HandleInput::VerifyToTarget(height, callback))
     }
 
-    /// Verify either to the latest block (if `height == None`) or to a given block (if `height == Some(height)`).
-    fn verify(
-        &mut self,
-        make_event: impl FnOnce(Callback<Result<LightBlock, Error>>) -> HandleInput,
-    ) -> Result<LightBlock, Error> {
-        let (sender, receiver) = channel::bounded::<Result<LightBlock, Error>>(1);
-
-        let callback = Callback::new(move |result| {
-            sender.send(result).unwrap();
-        });
-
-        let event = make_event(callback);
-        self.sender.send(event).unwrap();
-
-        receiver.recv().unwrap()
-    }
-
-    /// Async version of `verify_to_highest`.
-    ///
-    /// The given `callback` will be called asynchronously with the
-    /// verification result.
-    pub fn verify_to_highest_async(
+    fn verify_to_highest_async(
         &mut self,
         callback: impl FnOnce(Result<LightBlock, Error>) -> () + Send + 'static,
     ) {
         let event = HandleInput::VerifyToHighest(Callback::new(callback));
         self.sender.send(event).unwrap();
     }
 
-    /// Async version of `verify_to_target`.
-    ///
-    /// The given `callback` will be called asynchronously with the
-    /// verification result.
-    pub fn verify_to_target_async(
+    fn verify_to_target_async(
         &mut self,
         height: Height,
         callback: impl FnOnce(Result<LightBlock, Error>) -> () + Send + 'static,
@@ -390,8 +413,7 @@ impl Handle {
         self.sender.send(event).unwrap();
     }
 
-    /// Terminate the underlying supervisor.
-    pub fn terminate(&mut self) {
+    fn terminate(&mut self) {
         let (sender, receiver) = channel::bounded::<()>(1);
 
         let callback = Callback::new(move |_| {