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//! Cord is a data streaming platform for composing, aggregating and distributing
//! arbitrary streams. It uses a publish-subscribe model that allows multiple publishers
//! to share their streams via a Cord Broker. Subscribers can then compose custom sinks
//! using a regex-like pattern to access realtime data based on their individual
//! requirements.
//!
//! To interact with a Broker, we use this library:
//!
//! # Examples
//!
//! ```no_run
//! use cord_client::Client;
//!# use cord_client::errors::Error;
//!
//!# async fn test() -> Result<(), Error> {
//! let mut conn = Client::connect(("127.0.0.1", 7101)).await?;
//!
//! // Tell the broker we're going to provide the namespace /users
//! conn.provide("/users".into()).await?;
//!
//! // Start publishing events...
//! conn.event("/users/mark".into(), "Mark has joined").await?;
//!
//!# Ok(())
//!# }
//! ```
//!
//! # Cord CLI
//! For one-off interactions with a Broker, there is also the Cord CLI, which is
//! available via Cargo:
//!
//! ```text
//! $ cargo install cord-client
//! $ cord-client sub /namespaces
//! ```
//!
//! For more usage, check the usage guidelines on [cord-proj.org](https://cord-proj.org).
pub mod errors;
use cord_message::{errors::Error as MessageError, Codec, Message, Pattern};
use errors::{Error, ErrorKind, Result};
use futures::{
future::{self, try_select},
stream::SplitSink,
Sink, SinkExt, Stream, StreamExt, TryStreamExt,
};
use futures_locks::Mutex;
use tokio::{
net::{TcpStream, ToSocketAddrs},
sync::mpsc,
sync::oneshot,
};
use tokio_util::codec::Framed;
use std::{
collections::HashMap,
convert::Into,
ops::Drop,
pin::Pin,
result,
sync::Arc,
task::{Context, Poll},
};
/// The `Client` type alias defines the `Sink` type for communicating with a Broker.
///
/// This type alias should be used for normal operation in favour of consuming
/// `ClientConn` directly. This type is instantiated using
/// [`Client::connect`](struct.ClientConn.html#method.connect).
///
/// The reason for this alias' existence is so that the `Sink` can be overridden for
/// testing.
pub type Client = ClientConn<SplitSink<Framed<TcpStream, Codec>, Message>>;
/// The `ClientConn` manages the connection between you and a Cord Broker.
///
/// Using a generic `Sink` (`S`) allows us to build mocks for testing. However for normal
/// use, it is strongly recommended to use the type alias, [`Client`](type.Client.html).
pub struct ClientConn<S> {
sink: S,
inner: Arc<Inner>,
}
/// A `Subscriber` encapsulates a stream of events for a subscribed namespace. It is
/// created by [`Client::subscribe()`](struct.Client.html#method.subscribe).
///
/// # Examples
///
/// ```
///# use cord_client::{errors::Result, Client};
///# use futures::{future, StreamExt, TryFutureExt};
///
///# async fn test() -> Result<()> {
/// let mut conn = Client::connect(("127.0.0.1", 7101)).await?;
/// conn.subscribe("/users/".into())
/// .and_then(|sub| async {
/// sub.for_each(|(namespace, data)| {
/// // Handle the message...
/// dbg!("Received the namespace '{}' with data: {}", namespace, data);
/// future::ready(())
/// })
/// .await;
/// Ok(())
/// })
/// .await
///# }
/// ```
pub struct Subscriber {
receiver: mpsc::Receiver<Message>,
_inner: Arc<Inner>,
}
struct Inner {
receivers: Mutex<HashMap<Pattern, Vec<mpsc::Sender<Message>>>>,
detonator: Option<oneshot::Sender<()>>,
}
impl<S> ClientConn<S>
where
S: Sink<Message, Error = MessageError> + Unpin,
{
/// Connect to a broker
pub async fn connect<A>(addr: A) -> Result<Client>
where
A: ToSocketAddrs,
{
// This channel is used to shutdown the stream listener when the Client is dropped
let (det_tx, det_rx) = oneshot::channel();
// Connect to the broker
let sock = TcpStream::connect(addr).await?;
// Wrap socket in message codec
let framed = Framed::new(sock, Codec::default());
let (sink, stream) = framed.split();
// Setup the receivers map
let receivers = Mutex::new(HashMap::new());
let receivers_c = receivers.clone();
// Route the codec's stream to receivers
let router = Box::pin(
stream
.map_err(|e| Error::from_kind(ErrorKind::Message(e)))
.try_fold(receivers_c, |recv, message| async move {
route(&recv, message).await;
Ok(recv)
}),
);
tokio::spawn(try_select(router, det_rx));
Ok(ClientConn {
sink,
inner: Arc::new(Inner {
receivers,
detonator: Some(det_tx),
}),
})
}
/// Inform the broker that you will be providing a new namespace
pub async fn provide(&mut self, namespace: Pattern) -> Result<()> {
self.sink
.send(Message::Provide(namespace))
.await
.map_err(|e| ErrorKind::Message(e).into())
}
/// Inform the broker that you will no longer be providing a namespace
pub async fn revoke(&mut self, namespace: Pattern) -> Result<()> {
self.sink
.send(Message::Revoke(namespace))
.await
.map_err(|e| ErrorKind::Message(e).into())
}
/// Subscribe to another provider's namespace
///
/// # Examples
///
/// ```
///# use cord_client::{errors::Result, Client};
///# use futures::{future, StreamExt, TryFutureExt};
///
///# async fn test() -> Result<()> {
/// let mut conn = Client::connect(("127.0.0.1", 7101)).await?;
/// conn.subscribe("/users/".into())
/// .and_then(|sub| async {
/// sub.for_each(|(namespace, data)| {
/// // Handle the message...
/// dbg!("Received the namespace '{}' with data: {}", namespace, data);
/// future::ready(())
/// })
/// .await;
/// Ok(())
/// })
/// .await
///# }
/// ```
pub async fn subscribe(&mut self, namespace: Pattern) -> Result<Subscriber> {
let namespace_c = namespace.clone();
self.sink.send(Message::Subscribe(namespace)).await?;
let (tx, rx) = mpsc::channel(10);
self.inner
.receivers
.with(move |mut guard| {
(*guard)
.entry(namespace_c)
.or_insert_with(Vec::new)
.push(tx);
let ok: result::Result<_, ()> = Ok(());
future::ready(ok)
})
.await
.unwrap();
Ok(Subscriber {
receiver: rx,
_inner: self.inner.clone(),
})
}
/// Unsubscribe from another provider's namespace
pub async fn unsubscribe(&mut self, namespace: Pattern) -> Result<()> {
let namespace_c = namespace.clone();
self.sink.send(Message::Unsubscribe(namespace)).await?;
self.inner
.receivers
.with(move |mut guard| {
(*guard).remove(&namespace_c);
future::ready(())
})
.await;
Ok(())
}
/// Publish an event to your subscribers
pub async fn event<Str: Into<String>>(&mut self, namespace: Pattern, data: Str) -> Result<()> {
self.sink
.send(Message::Event(namespace, data.into()))
.await
.map_err(|e| ErrorKind::Message(e).into())
}
}
impl<E, S, T> Sink<T> for ClientConn<S>
where
S: Sink<T, Error = E>,
E: Into<Error>,
{
type Error = Error;
fn poll_ready(self: Pin<&mut Self>, cx: &mut Context) -> Poll<result::Result<(), Self::Error>> {
unsafe { Pin::map_unchecked_mut(self, |x| &mut x.sink) }
.poll_ready(cx)
.map_err(|e| e.into())
}
fn start_send(self: Pin<&mut Self>, item: T) -> result::Result<(), Self::Error> {
unsafe { Pin::map_unchecked_mut(self, |x| &mut x.sink) }
.start_send(item)
.map_err(|e| e.into())
}
fn poll_flush(self: Pin<&mut Self>, cx: &mut Context) -> Poll<result::Result<(), Self::Error>> {
unsafe { Pin::map_unchecked_mut(self, |x| &mut x.sink) }
.poll_flush(cx)
.map_err(|e| e.into())
}
fn poll_close(self: Pin<&mut Self>, cx: &mut Context) -> Poll<result::Result<(), Self::Error>> {
unsafe { Pin::map_unchecked_mut(self, |x| &mut x.sink) }
.poll_close(cx)
.map_err(|e| e.into())
}
}
impl Stream for Subscriber {
type Item = (Pattern, String);
fn poll_next(self: Pin<&mut Self>, cx: &mut Context) -> Poll<Option<Self::Item>> {
unsafe { Pin::map_unchecked_mut(self, |x| &mut x.receiver) }
.poll_recv(cx)
.map(|opt_msg| match opt_msg {
Some(Message::Event(pattern, data)) => Some((pattern, data)),
None => None,
_ => unreachable!(),
})
}
}
impl Drop for Inner {
fn drop(&mut self) {
// Ignore any error from the channel as an error indicates that the other side
// has already terminated.
let _ = self
.detonator
.take()
.expect("Inner has already been terminated")
.send(());
}
}
async fn route(receivers: &Mutex<HashMap<Pattern, Vec<mpsc::Sender<Message>>>>, message: Message) {
receivers
.with(move |mut guard| {
// Remove any subscribers that have no senders left
(*guard).retain(|namespace, senders| {
// We assume that all messages will be Events. If this changes, we will
// need to store a Message, not a pattern.
if namespace.contains(message.namespace()) {
// Remove any senders that give errors when attempting to send
senders.retain_mut(|tx| tx.try_send(message.clone()).is_ok());
}
// So long as we have senders, keep the subscriber
!senders.is_empty()
});
future::ready(())
})
.await
}
#[cfg(test)]
mod tests {
use super::*;
use cord_message::errors::ErrorKind as MessageErrorKind;
// Using Futures channel instead of Tokio as Tokio's channel implementation is
// missing a Sink implementation
use futures::channel::mpsc::{unbounded, UnboundedReceiver};
struct ForwardStream(Vec<Message>);
impl Stream for ForwardStream {
type Item = Result<Message>;
fn poll_next(mut self: Pin<&mut Self>, _: &mut Context) -> Poll<Option<Self::Item>> {
Poll::Ready(self.0.pop().map(Ok))
}
}
#[allow(clippy::type_complexity)]
fn setup_client() -> (
ClientConn<impl Sink<Message, Error = MessageError>>,
UnboundedReceiver<Message>,
Mutex<HashMap<Pattern, Vec<mpsc::Sender<Message>>>>,
) {
let (tx, rx) = unbounded();
let (det_tx, _) = oneshot::channel();
let receivers = Mutex::new(HashMap::new());
(
ClientConn {
sink: tx.sink_map_err(|e| MessageErrorKind::Msg(format!("{}", e)).into()),
inner: Arc::new(Inner {
receivers: receivers.clone(),
detonator: Some(det_tx),
}),
},
rx,
receivers,
)
}
#[tokio::test]
async fn test_forward() {
let (client, rx, _) = setup_client();
let data_stream = ForwardStream(vec![
Message::Event("/a".into(), "b".into()),
Message::Provide("/a".into()),
]);
data_stream.forward(client).await.unwrap();
// We check these messages in reverse order (i.e. Provide, then Event), because
// our budget DIY stream sends them in reverse order.
let (item, rx) = rx.into_future().await;
assert_eq!(item, Some(Message::Provide("/a".into())));
let (item, _) = rx.into_future().await;
assert_eq!(item, Some(Message::Event("/a".into(), "b".into())));
}
#[tokio::test]
async fn test_provide() {
let (mut client, rx, _) = setup_client();
client.provide("/a/b".into()).await.unwrap();
assert_eq!(
rx.into_future().await.0.unwrap(),
Message::Provide("/a/b".into())
);
}
#[tokio::test]
async fn test_revoke() {
let (mut client, rx, _) = setup_client();
client.revoke("/a/b".into()).await.unwrap();
assert_eq!(
rx.into_future().await.0.unwrap(),
Message::Revoke("/a/b".into())
);
}
#[tokio::test]
async fn test_subscribe() {
let (mut client, rx, receivers) = setup_client();
client.subscribe("/a/b".into()).await.unwrap();
// Check that the mock broker (`rx`) has received our message
assert_eq!(
rx.into_future().await.0.unwrap(),
Message::Subscribe("/a/b".into())
);
// Check that the `receivers` routing table has been updated
let guard = receivers.lock().await;
assert!((*guard).contains_key(&"/a/b".into()));
}
#[tokio::test]
async fn test_unsubscribe() {
let (mut client, rx, receivers) = setup_client();
receivers
.with(|mut guard| {
(*guard).insert("/a/b".into(), Vec::new());
future::ready(())
})
.await;
client.unsubscribe("/a/b".into()).await.unwrap();
// Check that the mock broker (`rx`) has received our message
assert_eq!(
rx.into_future().await.0.unwrap(),
Message::Unsubscribe("/a/b".into())
);
// Check that the `receivers` routing table has been updated
let guard = receivers.lock().await;
assert!((*guard).is_empty());
}
#[tokio::test]
async fn test_event() {
let (mut client, rx, _) = setup_client();
client.event("/a/b".into(), "moo").await.unwrap();
assert_eq!(
rx.into_future().await.0.unwrap(),
Message::Event("/a/b".into(), "moo".into())
);
}
#[tokio::test]
async fn test_route() {
let (tx, mut rx) = mpsc::channel(10);
let receivers = Mutex::new(HashMap::new());
receivers
.with(|mut guard| {
(*guard).insert("/a/b".into(), vec![tx]);
future::ready(())
})
.await;
let event_msg = Message::Event("/a/b".into(), "Moo!".into());
let event_msg_c = event_msg.clone();
route(&receivers, event_msg).await;
// Check that the subscriber has received our message
assert_eq!(rx.recv().await.unwrap(), event_msg_c);
let guard = receivers.lock().await;
assert!((*guard).contains_key(&"/a/b".into()));
}
#[tokio::test]
async fn test_route_norecv() {
let (tx, _) = mpsc::channel(10);
let receivers = Mutex::new(HashMap::new());
receivers
.with(|mut guard| {
(*guard).insert("/a/b".into(), vec![tx]);
future::ready(())
})
.await;
route(&receivers, Message::Event("/a/b".into(), "Moo!".into())).await;
// Check that the unused receiver has been removed
let guard = receivers.lock().await;
assert!((*guard).is_empty());
}
}