From 4e3d5ccac99b24934c972e088cd7eb02bb95df06 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Tue, 17 Jun 2025 02:11:45 -0400
Subject: Handlers are _named operations_, which can be exposed via routes.

Each domain module that exposes handlers does so through a `handlers` child module, ideally as a top-level symbol that can be plugged directly into Axum's `MethodRouter`. Modules could make exceptions to this - kill the doctrinaire inside yourself, after all - but none of the API modules that actually exist need such exceptions, and consistency is useful.

The related details of request types, URL types, response types, errors, &c &c are then organized into modules under `handlers`, along with their respective tests.
---
 src/event/handlers/stream/mod.rs | 85 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 src/event/handlers/stream/mod.rs

(limited to 'src/event/handlers/stream/mod.rs')

diff --git a/src/event/handlers/stream/mod.rs b/src/event/handlers/stream/mod.rs
new file mode 100644
index 0000000..d0d3f08
--- /dev/null
+++ b/src/event/handlers/stream/mod.rs
@@ -0,0 +1,85 @@
+use axum::{
+    extract::State,
+    response::{
+        self, IntoResponse,
+        sse::{self, Sse},
+    },
+};
+use axum_extra::extract::Query;
+use futures::stream::{Stream, StreamExt as _};
+
+use crate::{
+    app::App,
+    error::{Internal, Unauthorized},
+    event::{Event, Heartbeat::Heartbeat, Sequence, Sequenced as _, app, extract::LastEventId},
+    token::{app::ValidateError, extract::Identity},
+};
+
+#[cfg(test)]
+mod test;
+
+pub async fn handler(
+    State(app): State<App>,
+    identity: Identity,
+    last_event_id: Option<LastEventId<Sequence>>,
+    Query(query): Query<QueryParams>,
+) -> Result<Response<impl Stream<Item = Event> + std::fmt::Debug>, Error> {
+    let resume_at = last_event_id.map_or(query.resume_point, LastEventId::into_inner);
+
+    let stream = app.events().subscribe(resume_at).await?;
+    let stream = app.tokens().limit_stream(identity.token, stream).await?;
+
+    Ok(Response(stream))
+}
+
+#[derive(serde::Deserialize)]
+pub struct QueryParams {
+    pub resume_point: Sequence,
+}
+
+#[derive(Debug)]
+pub struct Response<S>(pub S);
+
+impl<S> IntoResponse for Response<S>
+where
+    S: Stream<Item = Event> + Send + 'static,
+{
+    fn into_response(self) -> response::Response {
+        let Self(stream) = self;
+        let stream = stream.map(sse::Event::try_from);
+        let heartbeat = match Heartbeat.try_into().map_err(Internal::from) {
+            Ok(heartbeat) => heartbeat,
+            Err(err) => return err.into_response(),
+        };
+        Sse::new(stream).keep_alive(heartbeat).into_response()
+    }
+}
+
+impl TryFrom<Event> for sse::Event {
+    type Error = serde_json::Error;
+
+    fn try_from(event: Event) -> Result<Self, Self::Error> {
+        let id = serde_json::to_string(&event.sequence())?;
+        let data = serde_json::to_string_pretty(&event)?;
+
+        let event = Self::default().id(id).data(data);
+
+        Ok(event)
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+#[error(transparent)]
+pub enum Error {
+    Subscribe(#[from] app::Error),
+    Validate(#[from] ValidateError),
+}
+
+impl IntoResponse for Error {
+    fn into_response(self) -> response::Response {
+        match self {
+            Self::Validate(ValidateError::InvalidToken) => Unauthorized.into_response(),
+            other => Internal::from(other).into_response(),
+        }
+    }
+}
-- 
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