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use std::collections::{BTreeMap, HashSet};
use axum::{
extract::State,
http::StatusCode,
response::{
sse::{self, Sse},
IntoResponse, Response,
},
routing::get,
Router,
};
use axum_extra::extract::Query;
use futures::{
future,
stream::{self, Stream, StreamExt as _, TryStreamExt as _},
};
use super::{extract::LastEventId, repo::broadcast};
use crate::{
app::App,
clock::RequestedAt,
error::Internal,
events::app::EventsError,
repo::{channel, login::Login},
};
#[cfg(test)]
mod test;
// For the purposes of event replay, an "event ID" is a vector of per-channel
// sequence numbers. Replay will start with messages whose sequence number in
// its channel is higher than the sequence in the event ID, or if the channel
// is not listed in the event ID, then at the beginning.
//
// Using a sorted map ensures that there is a canonical representation for
// each event ID.
type EventId = BTreeMap<channel::Id, broadcast::Sequence>;
pub fn router() -> Router<App> {
Router::new().route("/api/events", get(events))
}
#[derive(Clone, serde::Deserialize)]
struct EventsQuery {
#[serde(default, rename = "channel")]
channels: HashSet<channel::Id>,
}
async fn events(
State(app): State<App>,
RequestedAt(now): RequestedAt,
_: Login, // requires auth, but doesn't actually care who you are
last_event_id: Option<LastEventId<EventId>>,
Query(query): Query<EventsQuery>,
) -> Result<Events<impl Stream<Item = ReplayableEvent> + std::fmt::Debug>, ErrorResponse> {
let resume_at = last_event_id
.map(LastEventId::into_inner)
.unwrap_or_default();
let streams = stream::iter(query.channels)
.then(|channel| {
let app = app.clone();
let resume_at = resume_at.clone();
async move {
let resume_at = resume_at.get(&channel).copied();
let events = app
.events()
.subscribe(&channel, &now, resume_at)
.await?
.map(ChannelEvent::wrap(channel));
Ok::<_, EventsError>(events)
}
})
.try_collect::<Vec<_>>()
.await
// impl From would take more code; this is used once.
.map_err(ErrorResponse)?;
// We resume counting from the provided last-event-id mapping, rather than
// starting from scratch, so that the events in a resumed stream contain
// the full vector of channel IDs for their event IDs right off the bat,
// even before any events are actually delivered.
let stream = stream::select_all(streams).scan(resume_at, |sequences, event| {
let (channel, sequence) = event.event_id();
sequences.insert(channel, sequence);
let event = ReplayableEvent(sequences.clone(), event);
future::ready(Some(event))
});
Ok(Events(stream))
}
#[derive(Debug)]
struct Events<S>(S);
impl<S> IntoResponse for Events<S>
where
S: Stream<Item = ReplayableEvent> + Send + 'static,
{
fn into_response(self) -> Response {
let Self(stream) = self;
let stream = stream.map(sse::Event::try_from);
Sse::new(stream)
.keep_alive(sse::KeepAlive::default())
.into_response()
}
}
#[derive(Debug)]
struct ErrorResponse(EventsError);
impl IntoResponse for ErrorResponse {
fn into_response(self) -> Response {
let Self(error) = self;
match error {
not_found @ EventsError::ChannelNotFound(_) => {
(StatusCode::NOT_FOUND, not_found.to_string()).into_response()
}
other => Internal::from(other).into_response(),
}
}
}
#[derive(Debug)]
struct ReplayableEvent(EventId, ChannelEvent);
#[derive(Debug, serde::Serialize)]
struct ChannelEvent {
channel: channel::Id,
#[serde(flatten)]
message: broadcast::Message,
}
impl ChannelEvent {
fn wrap(channel: channel::Id) -> impl Fn(broadcast::Message) -> Self {
move |message| Self {
channel: channel.clone(),
message,
}
}
fn event_id(&self) -> (channel::Id, broadcast::Sequence) {
(self.channel.clone(), self.message.sequence)
}
}
impl TryFrom<ReplayableEvent> for sse::Event {
type Error = serde_json::Error;
fn try_from(value: ReplayableEvent) -> Result<Self, Self::Error> {
let ReplayableEvent(id, data) = value;
let id = serde_json::to_string(&id)?;
let data = serde_json::to_string_pretty(&data)?;
let event = Self::default().id(id).data(data);
Ok(event)
}
}
|
