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//! Semantic server-sent events (SSE) responder with a channel-like interface.
//!
//! # Examples
//! ```no_run
//! use std::{convert::Infallible, time::Duration};
//!
//! use actix_web::{get, Responder};
//! use actix_web_lab::sse;
//!
//! #[get("/from-channel")]
//! async fn from_channel() -> impl Responder {
//! let (sender, sse_stream) = sse::channel(10);
//!
//! // note: sender will typically be spawned or handed off somewhere else
//! let _ = sender.send(sse::Event::Comment("my comment".into())).await;
//! let _ = sender
//! .send(sse::Data::new("my data").event("chat_msg"))
//! .await;
//!
//! sse_stream.with_retry_duration(Duration::from_secs(10))
//! }
//!
//! #[get("/from-stream")]
//! async fn from_stream() -> impl Responder {
//! let event_stream = futures_util::stream::iter([Ok::<_, Infallible>(sse::Event::Data(
//! sse::Data::new("foo"),
//! ))]);
//!
//! sse::Sse::from_stream(event_stream).with_keep_alive(Duration::from_secs(5))
//! }
//! ```
//!
//! Complete usage examples can be found in the examples directory of the source code repo.
#![doc(
alias = "server sent",
alias = "server-sent",
alias = "server sent events",
alias = "server-sent events",
alias = "event-stream"
)]
use std::{
convert::Infallible,
pin::Pin,
task::{Context, Poll},
time::Duration,
};
use actix_web::{
body::{BodySize, BoxBody, MessageBody},
http::header::ContentEncoding,
HttpRequest, HttpResponse, Responder,
};
use bytes::{BufMut as _, Bytes, BytesMut};
use bytestring::ByteString;
use derive_more::{Display, Error};
use futures_core::Stream;
use pin_project_lite::pin_project;
use serde::Serialize;
use tokio::{
sync::mpsc,
time::{interval, Interval},
};
use crate::{
header::{CacheControl, CacheDirective},
BoxError,
};
/// Error returned from [`SseSender::send()`].
#[derive(Debug, Display, Error)]
#[display(fmt = "channel closed")]
#[non_exhaustive]
pub struct SendError(#[error(not(source))] Event);
#[doc(hidden)]
#[deprecated(
since = "0.17.0",
note = "Renamed to `SendError`. Prefer `sse::SendError`."
)]
pub type SseSendError = SendError;
/// Error returned from [`SseSender::try_send()`].
///
/// In each case, the original message is returned back to you.
#[derive(Debug, Display, Error)]
#[non_exhaustive]
pub enum TrySendError {
/// The SSE send buffer is full.
#[display(fmt = "buffer full")]
Full(#[error(not(source))] Event),
/// The receiving ([`Sse`]) has been dropped, likely because the client disconnected.
#[display(fmt = "channel closed")]
Closed(#[error(not(source))] Event),
}
#[doc(hidden)]
#[deprecated(
since = "0.17.0",
note = "Renamed to `TrySendError`. Prefer `sse::TrySendError`."
)]
pub type SseTrySendError = TrySendError;
/// Server-sent events data message containing a `data` field and optional `id` and `event` fields.
///
/// Since it implements `Into<SseMessage>`, this can be passed directly to [`send`](SseSender::send)
/// or [`try_send`](SseSender::try_send).
///
/// # Examples
/// ```
/// # #[actix_web::main] async fn test() {
/// use std::convert::Infallible;
///
/// use actix_web::body;
/// use actix_web_lab::sse;
/// use futures_util::stream;
/// use serde::Serialize;
///
/// #[derive(serde::Serialize)]
/// struct Foo {
/// bar: u32,
/// }
///
/// let sse = sse::Sse::from_stream(stream::iter([
/// Ok::<_, Infallible>(sse::Event::Data(sse::Data::new("foo"))),
/// Ok::<_, Infallible>(sse::Event::Data(
/// sse::Data::new_json(Foo { bar: 42 }).unwrap(),
/// )),
/// ]));
///
/// assert_eq!(
/// body::to_bytes(sse).await.unwrap(),
/// "data: foo\n\ndata: {\"bar\":42}\n\n",
/// );
/// # }; test();
/// ```
#[must_use]
#[derive(Debug, Clone)]
pub struct Data {
id: Option<ByteString>,
event: Option<ByteString>,
data: ByteString,
}
#[doc(hidden)]
#[deprecated(since = "0.17.0", note = "Renamed to `Data`. Prefer `sse::Data`.")]
pub type SseData = Data;
impl Data {
/// Constructs a new SSE data message with just the `data` field.
///
/// # Examples
/// ```
/// use actix_web_lab::sse;
/// let event = sse::Event::Data(sse::Data::new("foo"));
/// ```
pub fn new(data: impl Into<ByteString>) -> Self {
Self {
id: None,
event: None,
data: data.into(),
}
}
/// Constructs a new SSE data message the `data` field set to `data` serialized as JSON.
///
/// # Examples
/// ```
/// use actix_web_lab::sse;
///
/// #[derive(serde::Serialize)]
/// struct Foo {
/// bar: u32,
/// }
///
/// let event = sse::Event::Data(sse::Data::new_json(Foo { bar: 42 }).unwrap());
/// ```
pub fn new_json(data: impl Serialize) -> Result<Self, serde_json::Error> {
Ok(Self {
id: None,
event: None,
data: serde_json::to_string(&data)?.into(),
})
}
/// Sets `data` field.
pub fn set_data(&mut self, data: impl Into<ByteString>) {
self.data = data.into();
}
/// Sets `id` field, returning a new data message.
pub fn id(mut self, id: impl Into<ByteString>) -> Self {
self.id = Some(id.into());
self
}
/// Sets `id` field.
pub fn set_id(&mut self, id: impl Into<ByteString>) {
self.id = Some(id.into());
}
/// Sets `event` name field, returning a new data message.
pub fn event(mut self, event: impl Into<ByteString>) -> Self {
self.event = Some(event.into());
self
}
/// Sets `event` name field.
pub fn set_event(&mut self, event: impl Into<ByteString>) {
self.event = Some(event.into());
}
}
impl From<Data> for Event {
fn from(data: Data) -> Self {
Self::Data(data)
}
}
/// Server-sent events message containing one or more fields.
#[must_use]
#[derive(Debug, Clone)]
pub enum Event {
/// A `data` message with optional ID and event name.
///
/// Data messages looks like this in the response stream.
/// ```plain
/// event: foo
/// id: 42
/// data: my data
///
/// data: {
/// data: "multiline": "data"
/// data: }
/// ```
Data(Data),
/// A comment message.
///
/// Comments look like this in the response stream.
/// ```plain
/// : my comment
///
/// : another comment
/// ```
Comment(ByteString),
}
#[doc(hidden)]
#[deprecated(since = "0.17.0", note = "Renamed to `Event`. Prefer `sse::Event`.")]
pub type SseMessage = Event;
impl Event {
/// Splits data into lines and prepend each line with `prefix`.
fn line_split_with_prefix(buf: &mut BytesMut, prefix: &'static str, data: ByteString) {
// initial buffer size guess is len(data) + 10 lines of prefix + EOLs + EOF
buf.reserve(data.len() + (10 * (prefix.len() + 1)) + 1);
// append prefix + space + line to buffer
for line in data.split('\n') {
buf.put_slice(prefix.as_bytes());
buf.put_slice(line.as_bytes());
buf.put_u8(b'\n');
}
}
/// Serializes message into event-stream format.
fn into_bytes(self) -> Bytes {
let mut buf = BytesMut::new();
match self {
Event::Data(Data { id, event, data }) => {
if let Some(text) = id {
buf.put_slice(b"id: ");
buf.put_slice(text.as_bytes());
buf.put_u8(b'\n');
}
if let Some(text) = event {
buf.put_slice(b"event: ");
buf.put_slice(text.as_bytes());
buf.put_u8(b'\n');
}
Self::line_split_with_prefix(&mut buf, "data: ", data);
}
Event::Comment(text) => Self::line_split_with_prefix(&mut buf, ": ", text),
}
// final newline to mark end of message
buf.put_u8(b'\n');
buf.freeze()
}
/// Serializes retry message into event-stream format.
fn retry_to_bytes(retry: Duration) -> Bytes {
Bytes::from(format!("retry: {}\n\n", retry.as_millis()))
}
/// Serializes a keep-alive event-stream comment message into bytes.
const fn keep_alive_bytes() -> Bytes {
Bytes::from_static(b": keep-alive\n\n")
}
}
/// Sender half of a server-sent events stream.
#[must_use]
#[derive(Debug, Clone)]
pub struct Sender {
tx: mpsc::Sender<Event>,
}
#[doc(hidden)]
#[deprecated(since = "0.17.0", note = "Renamed to `Sender`. Prefer `sse::Sender`.")]
pub type SseSender = Sender;
impl Sender {
/// Send an SSE message.
///
/// # Errors
/// Errors if the receiving ([`Sse`]) has been dropped, likely because the client disconnected.
///
/// # Examples
/// ```
/// #[actix_web::main] async fn test() {
/// use actix_web_lab::sse;
///
/// let (sender, sse_stream) = sse::channel(5);
/// sender.send(sse::Data::new("my data").event("my event name")).await.unwrap();
/// sender.send(sse::Event::Comment("my comment".into())).await.unwrap();
/// # } test();
/// ```
pub async fn send(&self, msg: impl Into<Event>) -> Result<(), SendError> {
self.tx
.send(msg.into())
.await
.map_err(|mpsc::error::SendError(ev)| SendError(ev))
}
/// Tries to send SSE message.
///
/// # Errors
/// Errors if:
/// - the the SSE buffer is currently full;
/// - the receiving ([`Sse`]) has been dropped, likely because the client disconnected.
///
/// # Examples
/// ```
/// #[actix_web::main] async fn test() {
/// use actix_web_lab::sse;
///
/// let (sender, sse_stream) = sse::channel(5);
/// sender.try_send(sse::Data::new("my data").event("my event name")).unwrap();
/// sender.try_send(sse::Event::Comment("my comment".into())).unwrap();
/// # } test();
/// ```
pub fn try_send(&self, msg: impl Into<Event>) -> Result<(), TrySendError> {
self.tx.try_send(msg.into()).map_err(|err| match err {
mpsc::error::TrySendError::Full(ev) => TrySendError::Full(ev),
mpsc::error::TrySendError::Closed(ev) => TrySendError::Closed(ev),
})
}
}
pin_project! {
/// Server-sent events (`text/event-stream`) responder.
///
/// Constructed with an [SSE channel](channel) or [using your own stream](Self::from_stream).
#[must_use]
#[derive(Debug)]
pub struct Sse<S> {
#[pin]
stream: S,
keep_alive: Option<Interval>,
retry_interval: Option<Duration>,
}
}
impl<S, E> Sse<S>
where
S: Stream<Item = Result<Event, E>> + 'static,
E: Into<BoxError>,
{
/// Create an SSE response from a stream that yields SSE [Event]s.
pub fn from_stream(stream: S) -> Self {
Self {
stream,
keep_alive: None,
retry_interval: None,
}
}
}
impl<S> Sse<S> {
/// Enables "keep-alive" messages to be send in the event stream after a period of inactivity.
///
/// By default, no keep-alive is set up.
pub fn with_keep_alive(mut self, keep_alive_period: Duration) -> Self {
let mut int = interval(keep_alive_period);
int.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Delay);
self.keep_alive = Some(int);
self
}
/// Queues first event message to inform client of custom retry period.
///
/// Browsers default to retry every 3 seconds or so.
pub fn with_retry_duration(mut self, retry: Duration) -> Self {
self.retry_interval = Some(retry);
self
}
}
impl<S, E> Responder for Sse<S>
where
S: Stream<Item = Result<Event, E>> + 'static,
E: Into<BoxError>,
{
type Body = BoxBody;
fn respond_to(self, _req: &HttpRequest) -> HttpResponse<Self::Body> {
HttpResponse::Ok()
.content_type(mime::TEXT_EVENT_STREAM)
.insert_header(ContentEncoding::Identity)
.insert_header(CacheControl(vec![CacheDirective::NoCache]))
.body(self)
}
}
impl<S, E> MessageBody for Sse<S>
where
S: Stream<Item = Result<Event, E>>,
E: Into<BoxError>,
{
type Error = BoxError;
fn size(&self) -> BodySize {
BodySize::Stream
}
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Result<Bytes, Self::Error>>> {
let this = self.project();
if let Some(retry) = this.retry_interval.take() {
cx.waker().wake_by_ref();
return Poll::Ready(Some(Ok(Event::retry_to_bytes(retry))));
}
if let Poll::Ready(msg) = this.stream.poll_next(cx) {
return match msg {
Some(Ok(msg)) => Poll::Ready(Some(Ok(msg.into_bytes()))),
Some(Err(err)) => Poll::Ready(Some(Err(err.into()))),
None => Poll::Ready(None),
};
}
if let Some(ref mut keep_alive) = this.keep_alive {
if keep_alive.poll_tick(cx).is_ready() {
return Poll::Ready(Some(Ok(Event::keep_alive_bytes())));
}
}
Poll::Pending
}
}
/// Create server-sent events (SSE) channel pair.
///
/// The `buffer` argument controls how many unsent messages can be stored without waiting.
///
/// The first item in the tuple is the sender half. Much like a regular channel, it can be cloned,
/// sent to another thread/task, and send event messages to the response stream. It provides several
/// methods that represent the event-stream format.
///
/// The second item is the responder and can, therefore, be used as a handler return type directly.
/// The stream will be closed after all [senders](SseSender) are dropped.
///
/// Read more about server-sent events in [this MDN article][mdn-sse].
///
/// See [module docs](self) for usage example.
///
/// [mdn-sse]: https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events/Using_server-sent_events
pub fn channel(buffer: usize) -> (Sender, Sse<ChannelStream>) {
let (tx, rx) = mpsc::channel(buffer);
(
Sender { tx },
Sse {
stream: ChannelStream(rx),
keep_alive: None,
retry_interval: None,
},
)
}
/// Stream implementation for channel-based SSE [`Sender`].
#[derive(Debug)]
pub struct ChannelStream(mpsc::Receiver<Event>);
impl Stream for ChannelStream {
type Item = Result<Event, Infallible>;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
self.0.poll_recv(cx).map(|ev| ev.map(Ok))
}
}
#[cfg(test)]
mod tests {
use std::convert::Infallible;
use actix_web::{body, test::TestRequest};
use futures_util::{future::poll_fn, stream, task::noop_waker, FutureExt as _, StreamExt as _};
use tokio::time::sleep;
use super::*;
use crate::assert_response_matches;
#[test]
fn format_retry_message() {
assert_eq!(
Event::retry_to_bytes(Duration::from_millis(1)),
"retry: 1\n\n",
);
assert_eq!(
Event::retry_to_bytes(Duration::from_secs(10)),
"retry: 10000\n\n",
);
}
#[test]
fn line_split_format() {
let mut buf = BytesMut::new();
Event::line_split_with_prefix(&mut buf, "data: ", ByteString::from("foo"));
assert_eq!(buf, "data: foo\n");
let mut buf = BytesMut::new();
Event::line_split_with_prefix(&mut buf, "data: ", ByteString::from("foo\nbar"));
assert_eq!(buf, "data: foo\ndata: bar\n");
}
#[test]
fn into_bytes_format() {
assert_eq!(Event::Comment("foo".into()).into_bytes(), ": foo\n\n");
assert_eq!(
Event::Data(Data {
id: None,
event: None,
data: "foo".into()
})
.into_bytes(),
"data: foo\n\n"
);
assert_eq!(
Event::Data(Data {
id: None,
event: None,
data: "\n".into()
})
.into_bytes(),
"data: \ndata: \n\n"
);
assert_eq!(
Event::Data(Data {
id: Some("42".into()),
event: None,
data: "foo".into()
})
.into_bytes(),
"id: 42\ndata: foo\n\n"
);
assert_eq!(
Event::Data(Data {
id: None,
event: Some("bar".into()),
data: "foo".into()
})
.into_bytes(),
"event: bar\ndata: foo\n\n"
);
assert_eq!(
Event::Data(Data {
id: Some("42".into()),
event: Some("bar".into()),
data: "foo".into()
})
.into_bytes(),
"id: 42\nevent: bar\ndata: foo\n\n"
);
}
#[test]
fn retry_is_first_msg() {
let waker = noop_waker();
let mut cx = Context::from_waker(&waker);
{
let (_sender, mut sse) = channel(9);
assert!(Pin::new(&mut sse).poll_next(&mut cx).is_pending());
}
{
let (_sender, sse) = channel(9);
let mut sse = sse.with_retry_duration(Duration::from_millis(42));
match Pin::new(&mut sse).poll_next(&mut cx) {
Poll::Ready(Some(Ok(bytes))) => assert_eq!(bytes, "retry: 42\n\n"),
res => panic!("poll should return retry message, got {res:?}"),
}
}
}
#[actix_web::test]
async fn dropping_responder_causes_send_fails() {
let (sender, sse) = channel(9);
drop(sse);
assert!(sender.send(Data::new("late data")).await.is_err());
}
#[actix_web::test]
async fn sse_from_external_streams() {
let st = stream::empty::<Result<_, Infallible>>();
let sse = Sse::from_stream(st);
assert_eq!(body::to_bytes(sse).await.unwrap(), "");
let st = stream::once(async { Ok::<_, Infallible>(Event::Data(Data::new("foo"))) });
let sse = Sse::from_stream(st);
assert_eq!(body::to_bytes(sse).await.unwrap(), "data: foo\n\n");
let st = stream::repeat(Ok::<_, Infallible>(Event::Data(Data::new("foo")))).take(2);
let sse = Sse::from_stream(st);
assert_eq!(
body::to_bytes(sse).await.unwrap(),
"data: foo\n\ndata: foo\n\n",
);
}
#[actix_web::test]
async fn appropriate_headers_are_set_on_responder() {
let st = stream::empty::<Result<_, Infallible>>();
let sse = Sse::from_stream(st);
let res = sse.respond_to(&TestRequest::default().to_http_request());
assert_response_matches!(res, OK;
"content-type" => "text/event-stream"
"content-encoding" => "identity"
"cache-control" => "no-cache"
);
}
#[actix_web::test]
async fn messages_are_received_from_sender() {
let (sender, mut sse) = channel(9);
assert!(poll_fn(|cx| Pin::new(&mut sse).poll_next(cx))
.now_or_never()
.is_none());
sender.send(Data::new("bar").event("foo")).await.unwrap();
match poll_fn(|cx| Pin::new(&mut sse).poll_next(cx)).now_or_never() {
Some(Some(Ok(bytes))) => assert_eq!(bytes, "event: foo\ndata: bar\n\n"),
res => panic!("poll should return data message, got {res:?}"),
}
}
#[actix_web::test]
async fn keep_alive_is_sent() {
let waker = noop_waker();
let mut cx = Context::from_waker(&waker);
let (sender, sse) = channel(9);
let mut sse = sse.with_keep_alive(Duration::from_millis(4));
assert!(Pin::new(&mut sse).poll_next(&mut cx).is_pending());
sleep(Duration::from_millis(20)).await;
match Pin::new(&mut sse).poll_next(&mut cx) {
Poll::Ready(Some(Ok(bytes))) => assert_eq!(bytes, ": keep-alive\n\n"),
res => panic!("poll should return data message, got {res:?}"),
}
assert!(Pin::new(&mut sse).poll_next(&mut cx).is_pending());
sender.send(Data::new("foo")).await.unwrap();
match Pin::new(&mut sse).poll_next(&mut cx) {
Poll::Ready(Some(Ok(bytes))) => assert_eq!(bytes, "data: foo\n\n"),
res => panic!("poll should return data message, got {res:?}"),
}
}
}