Draft `websocket` example :tada:

8 files changed, 426 insertions, 73 deletions

diff --git a/Cargo.toml b/Cargo.toml
index bb50888a..e553c78f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -88,6 +88,7 @@ members = [
     "examples/tooltip",
     "examples/tour",
     "examples/url_handler",
+    "examples/websocket",
 ]
 
 [dependencies]
diff --git a/examples/download_progress/src/download.rs b/examples/download_progress/src/download.rs
index 06d5d3fd..20682e7a 100644
--- a/examples/download_progress/src/download.rs
+++ b/examples/download_progress/src/download.rs
@@ -10,6 +10,7 @@ pub fn file<I: 'static + Hash + Copy + Send, T: ToString>(
     url: T,
 ) -> iced::Subscription<(I, Progress)> {
     subscription::run(
+        id,
         Download {
             id,
             url: url.to_string(),
diff --git a/examples/websocket/Cargo.toml b/examples/websocket/Cargo.toml
new file mode 100644
index 00000000..6b4d9d10
--- /dev/null
+++ b/examples/websocket/Cargo.toml
@@ -0,0 +1,22 @@
+[package]
+name = "websocket"
+version = "0.1.0"
+authors = ["Héctor Ramón Jiménez <hector0193@gmail.com>"]
+edition = "2018"
+publish = false
+
+[dependencies]
+iced = { path = "../..", features = ["tokio", "debug"] }
+iced_native = { path = "../../native" }
+iced_futures = { path = "../../futures" }
+
+[dependencies.async-tungstenite]
+version = "0.16"
+features = ["tokio-rustls-webpki-roots"]
+
+[dependencies.tokio]
+version = "1"
+features = ["time"]
+
+[dependencies.warp]
+version = "0.3"
diff --git a/examples/websocket/README.md b/examples/websocket/README.md
new file mode 100644
index 00000000..fcdee9f3
--- /dev/null
+++ b/examples/websocket/README.md
@@ -0,0 +1,12 @@
+## Websocket
+
+A simple example that keeps a WebSocket connection open to an echo server.
+
+The __[`main`]__ file contains all the code of the example.
+
+You can run it with `cargo run`:
+```
+cargo run --package websocket
+```
+
+[`main`]: src/main.rs
diff --git a/examples/websocket/src/echo.rs b/examples/websocket/src/echo.rs
new file mode 100644
index 00000000..13596ddd
--- /dev/null
+++ b/examples/websocket/src/echo.rs
@@ -0,0 +1,146 @@
+pub mod server;
+
+use iced_futures::futures;
+use iced_native::subscription::{self, Subscription};
+
+use futures::channel::mpsc;
+use futures::sink::SinkExt;
+use futures::stream::StreamExt;
+
+use async_tungstenite::tungstenite;
+
+pub fn connect() -> Subscription<Event> {
+    struct Connect;
+
+    subscription::unfold(
+        std::any::TypeId::of::<Connect>(),
+        State::Disconnected,
+        |state| async move {
+            match state {
+                State::Disconnected => {
+                    const ECHO_SERVER: &str = "ws://localhost:3030";
+
+                    match async_tungstenite::tokio::connect_async(ECHO_SERVER)
+                        .await
+                    {
+                        Ok((websocket, _)) => {
+                            let (sender, receiver) = mpsc::channel(100);
+
+                            (
+                                Some(Event::Connected(Connection(sender))),
+                                State::Connected(websocket, receiver),
+                            )
+                        }
+                        Err(_) => {
+                            let _ = tokio::time::sleep(
+                                tokio::time::Duration::from_secs(1),
+                            )
+                            .await;
+
+                            (Some(Event::Disconnected), State::Disconnected)
+                        }
+                    }
+                }
+                State::Connected(mut websocket, mut input) => {
+                    let mut fused_websocket = websocket.by_ref().fuse();
+
+                    futures::select! {
+                        received = fused_websocket.select_next_some() => {
+                            match received {
+                                Ok(tungstenite::Message::Text(message)) => {
+                                    (
+                                        Some(Event::MessageReceived(Message::User(message))),
+                                        State::Connected(websocket, input)
+                                    )
+                                }
+                                Ok(_) => {
+                                    (None, State::Connected(websocket, input))
+                                }
+                                Err(_) => {
+                                    (Some(Event::Disconnected), State::Disconnected)
+                                }
+                            }
+                        }
+
+                        message = input.select_next_some() => {
+                            let result = websocket.send(tungstenite::Message::Text(String::from(message))).await;
+
+                            if result.is_ok() {
+                                (None, State::Connected(websocket, input))
+                            } else {
+                                (Some(Event::Disconnected), State::Disconnected)
+                            }
+                        }
+                    }
+                }
+            }
+        },
+    )
+}
+
+#[derive(Debug)]
+enum State {
+    Disconnected,
+    Connected(
+        async_tungstenite::WebSocketStream<
+            async_tungstenite::tokio::ConnectStream,
+        >,
+        mpsc::Receiver<Message>,
+    ),
+}
+
+#[derive(Debug, Clone)]
+pub enum Event {
+    Connected(Connection),
+    Disconnected,
+    MessageReceived(Message),
+}
+
+#[derive(Debug, Clone)]
+pub struct Connection(mpsc::Sender<Message>);
+
+impl Connection {
+    pub fn send(&mut self, message: Message) {
+        let _ = self
+            .0
+            .try_send(message)
+            .expect("Send message to echo server");
+    }
+}
+
+#[derive(Debug, Clone)]
+pub enum Message {
+    Connected,
+    Disconnected,
+    User(String),
+}
+
+impl Message {
+    pub fn new(message: &str) -> Option<Self> {
+        if message.is_empty() {
+            None
+        } else {
+            Some(Self::User(message.to_string()))
+        }
+    }
+
+    pub fn connected() -> Self {
+        Message::Connected
+    }
+
+    pub fn disconnected() -> Self {
+        Message::Disconnected
+    }
+}
+
+impl From<Message> for String {
+    fn from(message: Message) -> Self {
+        match message {
+            Message::Connected => String::from("Connected successfully!"),
+            Message::Disconnected => {
+                String::from("Connection lost... Retrying...")
+            }
+            Message::User(message) => message,
+        }
+    }
+}
diff --git a/examples/websocket/src/echo/server.rs b/examples/websocket/src/echo/server.rs
new file mode 100644
index 00000000..7702d417
--- /dev/null
+++ b/examples/websocket/src/echo/server.rs
@@ -0,0 +1,57 @@
+use iced_futures::futures;
+
+use futures::channel::mpsc;
+use futures::{SinkExt, StreamExt};
+use warp::ws::WebSocket;
+use warp::Filter;
+
+// Basic WebSocket echo server adapted from:
+// https://github.com/seanmonstar/warp/blob/3ff2eaf41eb5ac9321620e5a6434d5b5ec6f313f/examples/websockets_chat.rs
+//
+// Copyright (c) 2018-2020 Sean McArthur
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+pub async fn run() {
+    let routes = warp::path::end().and(warp::ws()).map(|ws: warp::ws::Ws| {
+        ws.on_upgrade(move |socket| user_connected(socket))
+    });
+
+    warp::serve(routes).run(([127, 0, 0, 1], 3030)).await;
+}
+
+async fn user_connected(ws: WebSocket) {
+    let (mut user_ws_tx, mut user_ws_rx) = ws.split();
+    let (mut tx, mut rx) = mpsc::unbounded();
+
+    tokio::task::spawn(async move {
+        while let Some(message) = rx.next().await {
+            let _ = user_ws_tx.send(message).await.unwrap_or_else(|e| {
+                eprintln!("websocket send error: {}", e);
+            });
+        }
+    });
+
+    while let Some(result) = user_ws_rx.next().await {
+        let msg = match result {
+            Ok(msg) => msg,
+            Err(_) => break,
+        };
+
+        let _ = tx.send(msg).await;
+    }
+}
diff --git a/examples/websocket/src/main.rs b/examples/websocket/src/main.rs
new file mode 100644
index 00000000..c03a9f3a
--- /dev/null
+++ b/examples/websocket/src/main.rs
@@ -0,0 +1,162 @@
+mod echo;
+
+use iced::alignment::{self, Alignment};
+use iced::button::{self, Button};
+use iced::executor;
+use iced::scrollable::{self, Scrollable};
+use iced::text_input::{self, TextInput};
+use iced::{
+    Application, Color, Column, Command, Container, Element, Length, Row,
+    Settings, Subscription, Text,
+};
+
+pub fn main() -> iced::Result {
+    WebSocket::run(Settings::default())
+}
+
+#[derive(Default)]
+struct WebSocket {
+    messages: Vec<echo::Message>,
+    message_log: scrollable::State,
+    new_message: String,
+    new_message_state: text_input::State,
+    new_message_button: button::State,
+    state: State,
+}
+
+#[derive(Debug, Clone)]
+enum Message {
+    NewMessageChanged(String),
+    Send(echo::Message),
+    Echo(echo::Event),
+    Server,
+}
+
+impl Application for WebSocket {
+    type Message = Message;
+    type Flags = ();
+    type Executor = executor::Default;
+
+    fn new(_flags: Self::Flags) -> (Self, Command<Message>) {
+        (
+            Self::default(),
+            Command::perform(echo::server::run(), |_| Message::Server),
+        )
+    }
+
+    fn title(&self) -> String {
+        String::from("WebSocket - Iced")
+    }
+
+    fn update(&mut self, message: Message) -> Command<Message> {
+        match message {
+            Message::NewMessageChanged(new_message) => {
+                self.new_message = new_message;
+            }
+            Message::Send(message) => match &mut self.state {
+                State::Connected(connection) => {
+                    self.new_message.clear();
+
+                    connection.send(message);
+                }
+                State::Disconnected => {}
+            },
+            Message::Echo(event) => match event {
+                echo::Event::Connected(connection) => {
+                    self.state = State::Connected(connection);
+
+                    self.messages.push(echo::Message::connected());
+                }
+                echo::Event::Disconnected => {
+                    self.state = State::Disconnected;
+
+                    self.messages.push(echo::Message::disconnected());
+                }
+                echo::Event::MessageReceived(message) => {
+                    self.messages.push(message);
+                    self.message_log.snap_to(1.0);
+                }
+            },
+            Message::Server => {}
+        }
+
+        Command::none()
+    }
+
+    fn subscription(&self) -> Subscription<Message> {
+        echo::connect().map(Message::Echo)
+    }
+
+    fn view(&mut self) -> Element<Message> {
+        let message_log = if self.messages.is_empty() {
+            Container::new(
+                Text::new("Your messages will appear here...")
+                    .color(Color::from_rgb8(0x88, 0x88, 0x88)),
+            )
+            .width(Length::Fill)
+            .height(Length::Fill)
+            .center_x()
+            .center_y()
+            .into()
+        } else {
+            self.messages
+                .iter()
+                .cloned()
+                .fold(
+                    Scrollable::new(&mut self.message_log),
+                    |scrollable, message| scrollable.push(Text::new(message)),
+                )
+                .width(Length::Fill)
+                .height(Length::Fill)
+                .spacing(10)
+                .into()
+        };
+
+        let new_message_input = {
+            let mut input = TextInput::new(
+                &mut self.new_message_state,
+                "Type a message...",
+                &self.new_message,
+                Message::NewMessageChanged,
+            )
+            .padding(10);
+
+            let mut button = Button::new(
+                &mut self.new_message_button,
+                Text::new("Send")
+                    .height(Length::Fill)
+                    .vertical_alignment(alignment::Vertical::Center),
+            )
+            .padding([0, 20]);
+
+            if matches!(self.state, State::Connected(_)) {
+                if let Some(message) = echo::Message::new(&self.new_message) {
+                    input = input.on_submit(Message::Send(message.clone()));
+                    button = button.on_press(Message::Send(message));
+                }
+            }
+
+            Row::with_children(vec![input.into(), button.into()])
+                .spacing(10)
+                .align_items(Alignment::Fill)
+        };
+
+        Column::with_children(vec![message_log, new_message_input.into()])
+            .width(Length::Fill)
+            .height(Length::Fill)
+            .padding(20)
+            .spacing(10)
+            .into()
+    }
+}
+
+enum State {
+    Disconnected,
+    Connected(echo::Connection),
+}
+
+impl Default for State {
+    fn default() -> Self {
+        Self::Disconnected
+    }
+}
diff --git a/native/src/subscription.rs b/native/src/subscription.rs
index 85ad96fa..70cd269e 100644
--- a/native/src/subscription.rs
+++ b/native/src/subscription.rs
@@ -2,7 +2,6 @@
 use crate::event::{self, Event};
 use crate::Hasher;
 
-use iced_futures::futures::channel::mpsc;
 use iced_futures::futures::{self, Future, Stream};
 use iced_futures::BoxStream;
 
@@ -59,21 +58,9 @@ pub fn events_with<Message>(
 where
     Message: 'static + Send,
 {
-    #[derive(Debug, Clone, Copy, Hash)]
-    struct Events(u64);
-
-    let hash = {
-        use std::hash::Hasher as _;
-
-        let mut hasher = Hasher::default();
-
-        f.hash(&mut hasher);
-
-        hasher.finish()
-    };
-
     Subscription::from_recipe(Runner {
-        initial: Events(hash),
+        id: f,
+        initial: (),
         spawn: move |_, events| {
             use futures::future;
             use futures::stream::StreamExt;
@@ -89,16 +76,19 @@ where
 /// [`Stream`] returned by the provided closure.
 ///
 /// The `initial` state will be used to uniquely identify the [`Subscription`].
-pub fn run<T, S, Message>(
+pub fn run<I, T, S, Message>(
+    id: I,
     initial: T,
     f: impl FnOnce(T) -> S + 'static,
 ) -> Subscription<Message>
 where
-    Message: 'static,
-    T: Clone + Hash + 'static,
+    I: Hash + 'static,
+    T: 'static,
     S: Stream<Item = Message> + Send + 'static,
+    Message: 'static,
 {
     Subscription::from_recipe(Runner {
+        id,
         initial,
         spawn: move |initial, _| f(initial),
     })
@@ -108,79 +98,41 @@ where
 /// [`Stream`] that will call the provided closure to produce every `Message`.
 ///
 /// The `initial` state will be used to uniquely identify the [`Subscription`].
-pub fn unfold<T, Fut, Message>(
+pub fn unfold<I, T, Fut, Message>(
+    id: I,
     initial: T,
     mut f: impl FnMut(T) -> Fut + Send + Sync + 'static,
 ) -> Subscription<Message>
 where
-    Message: 'static,
-    T: Clone + Hash + Send + 'static,
-    Fut: Future<Output = (Message, T)> + Send + 'static,
-{
-    use futures::future::FutureExt;
-
-    run(initial, move |initial| {
-        futures::stream::unfold(initial, move |state| f(state).map(Some))
-    })
-}
-
-/// Returns a [`Subscription`] that will open a channel and asynchronously run a
-/// [`Stream`] that will call the provided closure to produce every `Message`.
-///
-/// When the [`Subscription`] starts, an `on_ready` message will be produced
-/// containing the [`mpsc::Sender`] end of the channel, which can be used by
-/// the parent application to send `Input` to the running [`Subscription`].
-///
-/// The provided closure should use the [`mpsc::Receiver`] argument to await for
-/// any `Input`.
-///
-/// This function is really useful to create asynchronous workers with
-/// bidirectional communication with a parent application.
-///
-/// The `initial` state will be used to uniquely identify the [`Subscription`].
-pub fn worker<T, Fut, Message, Input>(
-    initial: T,
-    on_ready: impl FnOnce(mpsc::Sender<Input>) -> Message + 'static,
-    f: impl FnMut(T, &mut mpsc::Receiver<Input>) -> Fut + Send + Sync + 'static,
-) -> Subscription<Message>
-where
-    T: Clone + Hash + Send + 'static,
-    Fut: Future<Output = (Message, T)> + Send + 'static,
-    Message: Send + 'static,
-    Input: Send + 'static,
+    I: Hash + 'static,
+    T: Send + 'static,
+    Fut: Future<Output = (Option<Message>, T)> + Send + 'static,
+    Message: 'static + Send,
 {
-    use futures::future;
+    use futures::future::{self, FutureExt};
     use futures::stream::StreamExt;
 
-    run(initial, move |initial| {
-        let (sender, receiver) = mpsc::channel(100);
-
-        futures::stream::once(future::ready(on_ready(sender))).chain(
-            futures::stream::unfold(
-                (f, initial, receiver),
-                move |(mut f, state, mut receiver)| async {
-                    let (message, state) = f(state, &mut receiver).await;
-
-                    Some((message, (f, state, receiver)))
-                },
-            ),
-        )
+    run(id, initial, move |initial| {
+        futures::stream::unfold(initial, move |state| f(state).map(Some))
+            .filter_map(future::ready)
     })
 }
 
-struct Runner<T, F, S, Message>
+struct Runner<I, T, F, S, Message>
 where
     F: FnOnce(T, EventStream) -> S,
     S: Stream<Item = Message>,
 {
+    id: I,
     initial: T,
     spawn: F,
 }
 
-impl<T, S, F, Message> Recipe<Hasher, (Event, event::Status)>
-    for Runner<T, F, S, Message>
+impl<I, T, S, F, Message> Recipe<Hasher, (Event, event::Status)>
+    for Runner<I, T, F, S, Message>
 where
-    T: Clone + Hash + 'static,
+    I: Hash + 'static,
+    T: 'static,
     F: FnOnce(T, EventStream) -> S,
     S: Stream<Item = Message> + Send + 'static,
 {
@@ -189,7 +141,7 @@ where
     fn hash(&self, state: &mut Hasher) {
         std::any::TypeId::of::<T>().hash(state);
 
-        self.initial.hash(state);
+        self.id.hash(state);
     }
 
     fn stream(self: Box<Self>, input: EventStream) -> BoxStream<Self::Output> {