Add event response handling

Signed-off-by: trivernis <trivernis@protonmail.com>

src/error.rs

@@ -1,4 +1,5 @@
 use thiserror::Error;
+use tokio::sync::oneshot;
 
 pub type Result<T> = std::result::Result<T, Error>;
 
@@ -18,6 +19,9 @@ pub enum Error {
 
     #[error("{0}")]
     Message(String),
+
+    #[error("Channel Error: {0}")]
+    ReceiveError(#[from] oneshot::error::RecvError),
 }
 
 impl From<String> for Error {

src/events/event.rs

@@ -65,4 +65,15 @@ impl Event {
 
         Ok(event_bytes)
     }
+
+    /// The identifier of the message
+    pub fn id(&self) -> u64 {
+        self.id
+    }
+
+    /// The ID of the message referenced by this message.
+    /// It represents the message that is replied to and can be None.
+    pub fn reference_id(&self) -> Option<u64> {
+        self.ref_id.clone()
+    }
 }

src/ipc/builder.rs

@@ -5,7 +5,6 @@ use crate::events::event_handler::EventHandler;
 use crate::ipc::client::IPCClient;
 use crate::ipc::context::Context;
 use crate::ipc::server::IPCServer;
-use crate::ipc::stream_emitter::StreamEmitter;
 use std::future::Future;
 use std::pin::Pin;
 
@@ -85,15 +84,15 @@ impl IPCBuilder {
     }
 
     /// Builds an ipc client
-    pub async fn build_client(self) -> Result<StreamEmitter> {
+    pub async fn build_client(self) -> Result<Context> {
         self.validate()?;
         let client = IPCClient {
             handler: self.handler,
         };
 
-        let emitter = client.connect(&self.address.unwrap()).await?;
+        let ctx = client.connect(&self.address.unwrap()).await?;
 
-        Ok(emitter)
+        Ok(ctx)
     }
 
     /// Validates that all required fields have been provided

src/ipc/client.rs

@@ -16,17 +16,20 @@ pub struct IPCClient {
 impl IPCClient {
     /// Connects to a given address and returns an emitter for events to that address.
     /// Invoked by [IPCBuilder::build_client](crate::builder::IPCBuilder::build_client)
-    pub async fn connect(self, address: &str) -> Result<StreamEmitter> {
+    pub async fn connect(self, address: &str) -> Result<Context> {
         let stream = TcpStream::connect(address).await?;
         let (read_half, write_half) = stream.into_split();
         let emitter = StreamEmitter::new(write_half);
         let ctx = Context::new(StreamEmitter::clone(&emitter));
         let handler = Arc::new(self.handler);
 
-        tokio::spawn(async move {
-            handle_connection(handler, read_half, ctx).await;
+        tokio::spawn({
+            let ctx = Context::clone(&ctx);
+            async move {
+                handle_connection(handler, read_half, ctx).await;
+            }
         });
 
-        Ok(emitter)
+        Ok(ctx)
     }
 }

src/ipc/context.rs

@@ -1,4 +1,9 @@
+use crate::error::Result;
 use crate::ipc::stream_emitter::StreamEmitter;
+use crate::Event;
+use std::collections::HashMap;
+use std::sync::Arc;
+use tokio::sync::{oneshot, Mutex};
 
 /// An object provided to each callback function.
 /// Currently it only holds the event emitter to emit response events in event callbacks.
@@ -18,10 +23,33 @@ use crate::ipc::stream_emitter::StreamEmitter;
 pub struct Context {
     /// The event emitter
     pub emitter: StreamEmitter,
+
+    reply_listeners: Arc<Mutex<HashMap<u64, oneshot::Sender<Event>>>>,
 }
 
 impl Context {
     pub(crate) fn new(emitter: StreamEmitter) -> Self {
-        Self { emitter }
+        Self {
+            emitter,
+            reply_listeners: Arc::new(Mutex::new(HashMap::new())),
+        }
+    }
+
+    /// Waits for a reply to the given message ID
+    pub async fn await_reply(&self, message_id: u64) -> Result<Event> {
+        let (rx, tx) = oneshot::channel();
+        {
+            let mut listeners = self.reply_listeners.lock().await;
+            listeners.insert(message_id, rx);
+        }
+        let event = tx.await?;
+
+        Ok(event)
+    }
+
+    /// Returns the channel for a reply to the given message id
+    pub(crate) async fn get_reply_sender(&self, ref_id: u64) -> Option<oneshot::Sender<Event>> {
+        let mut listeners = self.reply_listeners.lock().await;
+        listeners.remove(&ref_id)
     }
 }

src/ipc/mod.rs

@@ -14,28 +14,41 @@ pub mod stream_emitter;
 /// Handles listening to a connection and triggering the corresponding event functions
 async fn handle_connection(handler: Arc<EventHandler>, mut read_half: OwnedReadHalf, ctx: Context) {
     while let Ok(event) = Event::from_async_read(&mut read_half).await {
-        let ctx = Context::clone(&ctx);
-        let handler = Arc::clone(&handler);
-
-        tokio::spawn(async move {
-            if let Err(e) = handler.handle_event(&ctx, event).await {
-                // emit an error event
-                if let Err(e) = ctx
-                    .emitter
-                    .emit(
-                        ERROR_EVENT_NAME,
-                        ErrorEventData {
-                            message: format!("{:?}", e),
-                            code: 500,
-                        },
-                    )
-                    .await
-                {
-                    log::error!("Error occurred when sending error response: {:?}", e);
+        // check if the event is a reply
+        if let Some(ref_id) = event.reference_id() {
+            // get the listener for replies
+            if let Some(sender) = ctx.get_reply_sender(ref_id).await {
+                // try sending the event to the listener for replies
+                if let Err(event) = sender.send(event) {
+                    handle_event(Context::clone(&ctx), Arc::clone(&handler), event);
                 }
-                log::error!("Failed to handle event: {:?}", e);
+                continue;
             }
-        });
+        }
+        handle_event(Context::clone(&ctx), Arc::clone(&handler), event);
     }
     log::debug!("Connection closed.");
 }
+
+/// Handles a single event in a different tokio context
+fn handle_event(ctx: Context, handler: Arc<EventHandler>, event: Event) {
+    tokio::spawn(async move {
+        if let Err(e) = handler.handle_event(&ctx, event).await {
+            // emit an error event
+            if let Err(e) = ctx
+                .emitter
+                .emit(
+                    ERROR_EVENT_NAME,
+                    ErrorEventData {
+                        message: format!("{:?}", e),
+                        code: 500,
+                    },
+                )
+                .await
+            {
+                log::error!("Error occurred when sending error response: {:?}", e);
+            }
+            log::error!("Failed to handle event: {:?}", e);
+        }
+    });
+}

src/ipc/stream_emitter.rs

@@ -1,3 +1,4 @@
+use crate::context::Context;
 use crate::error::Result;
 use crate::events::event::Event;
 use serde::Serialize;
@@ -26,7 +27,7 @@ impl StreamEmitter {
         event: &str,
         data: T,
         res_id: Option<u64>,
-    ) -> Result<()> {
+    ) -> Result<EmitMetadata> {
         let data_bytes = rmp_serde::to_vec(&data)?;
         let event = Event::new(event.to_string(), data_bytes, res_id);
         let event_bytes = event.to_bytes()?;
@@ -35,14 +36,14 @@ impl StreamEmitter {
             (*stream).write_all(&event_bytes[..]).await?;
         }
 
-        Ok(())
+        Ok(EmitMetadata::new(event.id()))
     }
 
     /// Emits an event
-    pub async fn emit<T: Serialize>(&self, event: &str, data: T) -> Result<()> {
-        self._emit(event, data, None).await?;
+    pub async fn emit<T: Serialize>(&self, event: &str, data: T) -> Result<EmitMetadata> {
+        let metadata = self._emit(event, data, None).await?;
 
-        Ok(())
+        Ok(metadata)
     }
 
     /// Emits a response to an event
@@ -51,9 +52,32 @@ impl StreamEmitter {
         event_id: u64,
         event: &str,
         data: T,
-    ) -> Result<()> {
-        self._emit(event, data, Some(event_id)).await?;
+    ) -> Result<EmitMetadata> {
+        let metadata = self._emit(event, data, Some(event_id)).await?;
 
-        Ok(())
+        Ok(metadata)
+    }
+}
+
+/// A metadata object returned after emitting an event.
+/// This object can be used to wait for a response to an event.
+pub struct EmitMetadata {
+    message_id: u64,
+}
+
+impl EmitMetadata {
+    pub(crate) fn new(message_id: u64) -> Self {
+        Self { message_id }
+    }
+
+    /// The ID of the emitted message
+    pub fn message_id(&self) -> u64 {
+        self.message_id
+    }
+
+    /// Waits for a reply to the given message.
+    pub async fn await_reply(&self, ctx: &Context) -> Result<Event> {
+        let reply = ctx.await_reply(self.message_id).await?;
+        Ok(reply)
     }
 }

src/lib.rs

@@ -6,17 +6,19 @@
 //! // create the client
 //! # async fn a() {
 //!
-//! let emitter = IPCBuilder::new()
+//! let ctx = IPCBuilder::new()
 //!     .address("127.0.0.1:2020")
 //!     // register callback
-//!     .on("ping", |_ctx, _event| Box::pin(async move {
+//!     .on("ping", |ctx, event| Box::pin(async move {
 //!         println!("Received ping event.");
+//!         ctx.emitter.emit_response(event.id(), "pong", ()).await?;
 //!         Ok(())
 //!     }))
 //!     .build_client().await.unwrap();
 //!
 //! // emit an initial event
-//! emitter.emit("ping", ()).await.unwrap();
+//! let response = ctx.emitter.emit("ping", ()).await.unwrap().await_reply(&ctx).await.unwrap();
+//! assert_eq!(response.name(), "pong");
 //! # }
 //! ```
 //!
@@ -28,8 +30,9 @@
 //! IPCBuilder::new()
 //!     .address("127.0.0.1:2020")
 //!     // register callback
-//!     .on("ping", |_ctx, _event| Box::pin(async move {
+//!     .on("ping", |ctx, event| Box::pin(async move {
 //!         println!("Received ping event.");
+//!         ctx.emitter.emit_response(event.id(), "pong", ()).await?;
 //!         Ok(())
 //!     }))
 //!     .build_server().await.unwrap();

src/tests/ipc_tests.rs

@@ -2,26 +2,22 @@ use self::super::utils::PingEventData;
 use crate::error::Error;
 use crate::events::error_event::ErrorEventData;
 use crate::IPCBuilder;
-use std::sync::atomic::{AtomicBool, AtomicU8, Ordering};
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Arc;
 use std::time::{Duration, SystemTime};
 
 #[tokio::test]
 async fn it_receives_events() {
-    let ctr = Arc::new(AtomicU8::new(0));
     let builder = IPCBuilder::new()
         .on("ping", {
-            let ctr = Arc::clone(&ctr);
             move |ctx, e| {
-                let ctr = Arc::clone(&ctr);
                 Box::pin(async move {
-                    ctr.fetch_add(1, Ordering::Relaxed);
                     let mut ping_data = e.data::<PingEventData>()?;
                     ping_data.time = SystemTime::now();
                     ping_data.ttl -= 1;
 
                     if ping_data.ttl > 0 {
-                        ctx.emitter.emit("ping", ping_data).await?;
+                        ctx.emitter.emit_response(e.id(), "pong", ping_data).await?;
                     }
 
                     Ok(())
@@ -41,8 +37,9 @@ async fn it_receives_events() {
     while !server_running.load(Ordering::Relaxed) {
         tokio::time::sleep(Duration::from_millis(10)).await;
     }
-    let client = builder.build_client().await.unwrap();
-    client
+    let ctx = builder.build_client().await.unwrap();
+    let reply = ctx
+        .emitter
         .emit(
             "ping",
             PingEventData {
@@ -51,9 +48,11 @@ async fn it_receives_events() {
             },
         )
         .await
+        .unwrap()
+        .await_reply(&ctx)
+        .await
         .unwrap();
-    tokio::time::sleep(Duration::from_secs(1)).await;
-    assert_eq!(ctr.load(Ordering::SeqCst), 16);
+    assert_eq!(reply.name(), "pong");
 }
 
 #[tokio::test]
@@ -91,8 +90,8 @@ async fn it_handles_errors() {
     while !server_running.load(Ordering::Relaxed) {
         tokio::time::sleep(Duration::from_millis(10)).await;
     }
-    let client = builder.build_client().await.unwrap();
-    client.emit("ping", ()).await.unwrap();
+    let ctx = builder.build_client().await.unwrap();
+    ctx.emitter.emit("ping", ()).await.unwrap();
 
     tokio::time::sleep(Duration::from_secs(1)).await;
     assert!(error_occurred.load(Ordering::SeqCst));