From a4dcc4b5c53966f3c4366e414a3e39d094f21404 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Fri, 20 Sep 2024 23:27:59 -0400
Subject: Push the handling of the `Last-Event-Id` _format_ inside of
 `channels::app`.

This is intended to make it a bit more opaque to callers, and to free me up to experiment with the event ID format. It also makes event IDs tractable for testing.
---
 src/events/app.rs    |  4 +--
 src/events/routes.rs | 77 +++++++++++++++++++++++++---------------------------
 2 files changed, 39 insertions(+), 42 deletions(-)

(limited to 'src/events')

diff --git a/src/events/app.rs b/src/events/app.rs
index dfb23d7..c3a027d 100644
--- a/src/events/app.rs
+++ b/src/events/app.rs
@@ -54,7 +54,7 @@ impl Broadcaster {
 
     // panic: if ``channel`` has not been previously registered, and was not
     // part of the initial set of channels.
-    pub fn broadcast(&self, channel: &channel::Id, message: broadcast::Message) {
+    pub fn broadcast(&self, channel: &channel::Id, message: &broadcast::Message) {
         let tx = self.sender(channel);
 
         // Per the Tokio docs, the returned error is only used to indicate that
@@ -64,7 +64,7 @@ impl Broadcaster {
         //
         // The successful return value, which includes the number of active
         // receivers, also isn't that interesting to us.
-        let _ = tx.send(message);
+        let _ = tx.send(message.clone());
     }
 
     // panic: if ``channel`` has not been previously registered, and was not
diff --git a/src/events/routes.rs b/src/events/routes.rs
index f880c70..ce5b778 100644
--- a/src/events/routes.rs
+++ b/src/events/routes.rs
@@ -9,7 +9,7 @@ use axum::{
     Router,
 };
 use axum_extra::extract::Query;
-use chrono::{self, format::SecondsFormat, DateTime};
+use chrono::{self, format::SecondsFormat};
 use futures::stream::{self, Stream, StreamExt as _, TryStreamExt as _};
 
 use super::repo::broadcast;
@@ -23,7 +23,7 @@ use crate::{
 };
 
 pub fn router() -> Router<App> {
-    Router::new().route("/api/events", get(on_events))
+    Router::new().route("/api/events", get(events))
 }
 
 #[derive(serde::Deserialize)]
@@ -32,20 +32,14 @@ struct EventsQuery {
     channels: Vec<channel::Id>,
 }
 
-async fn on_events(
+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>,
     Query(query): Query<EventsQuery>,
-) -> Result<Events<impl Stream<Item = ChannelEvent<broadcast::Message>>>, ErrorResponse> {
-    let resume_at = last_event_id
-        .map(|LastEventId(header)| header)
-        .map(|header| DateTime::parse_from_rfc3339(&header))
-        .transpose()
-        // impl From would take more code; this is used once.
-        .map_err(ErrorResponse::LastEventIdError)?
-        .map(|ts| ts.to_utc());
+) -> Result<Events<impl Stream<Item = ChannelEvent>>, ErrorResponse> {
+    let resume_at = last_event_id.as_deref();
 
     let streams = stream::iter(query.channels)
         .then(|channel| {
@@ -53,7 +47,7 @@ async fn on_events(
             async move {
                 let events = app
                     .channels()
-                    .events(&channel, &now, resume_at.as_ref())
+                    .events(&channel, &now, resume_at)
                     .await?
                     .map(ChannelEvent::wrap(channel));
 
@@ -63,7 +57,7 @@ async fn on_events(
         .try_collect::<Vec<_>>()
         .await
         // impl From would take more code; this is used once.
-        .map_err(ErrorResponse::EventsError)?;
+        .map_err(ErrorResponse)?;
 
     let stream = stream::select_all(streams);
 
@@ -74,60 +68,63 @@ struct Events<S>(S);
 
 impl<S> IntoResponse for Events<S>
 where
-    S: Stream<Item = ChannelEvent<broadcast::Message>> + Send + 'static,
+    S: Stream<Item = ChannelEvent> + Send + 'static,
 {
     fn into_response(self) -> Response {
         let Self(stream) = self;
-        let stream = stream.map(to_sse_event);
+        let stream = stream.map(sse::Event::try_from);
         Sse::new(stream)
             .keep_alive(sse::KeepAlive::default())
             .into_response()
     }
 }
 
-enum ErrorResponse {
-    EventsError(EventsError),
-    LastEventIdError(chrono::ParseError),
-}
+struct ErrorResponse(EventsError);
 
 impl IntoResponse for ErrorResponse {
     fn into_response(self) -> Response {
-        match self {
-            Self::EventsError(not_found @ EventsError::ChannelNotFound(_)) => {
+        let Self(error) = self;
+        match error {
+            not_found @ EventsError::ChannelNotFound(_) => {
                 (StatusCode::NOT_FOUND, not_found.to_string()).into_response()
             }
-            Self::EventsError(other) => InternalError::from(other).into_response(),
-            Self::LastEventIdError(other) => {
-                (StatusCode::BAD_REQUEST, other.to_string()).into_response()
+            resume_at @ EventsError::ResumeAtError(_) => {
+                (StatusCode::BAD_REQUEST, resume_at.to_string()).into_response()
             }
+            other => InternalError::from(other).into_response(),
         }
     }
 }
 
-fn to_sse_event(event: ChannelEvent<broadcast::Message>) -> Result<sse::Event, serde_json::Error> {
-    let data = serde_json::to_string_pretty(&event)?;
-    let event = sse::Event::default()
-        .id(event
-            .message
-            .sent_at
-            .to_rfc3339_opts(SecondsFormat::AutoSi, /* use_z */ true))
-        .data(&data);
-
-    Ok(event)
-}
-
 #[derive(serde::Serialize)]
-struct ChannelEvent<M> {
+struct ChannelEvent {
     channel: channel::Id,
     #[serde(flatten)]
-    message: M,
+    message: broadcast::Message,
 }
 
-impl<M> ChannelEvent<M> {
-    fn wrap(channel: channel::Id) -> impl Fn(M) -> Self {
+impl ChannelEvent {
+    fn wrap(channel: channel::Id) -> impl Fn(broadcast::Message) -> Self {
         move |message| Self {
             channel: channel.clone(),
             message,
         }
     }
+
+    fn event_id(&self) -> String {
+        self.message
+            .sent_at
+            .to_rfc3339_opts(SecondsFormat::AutoSi, /* use_z */ true)
+    }
+}
+
+impl TryFrom<ChannelEvent> for sse::Event {
+    type Error = serde_json::Error;
+
+    fn try_from(value: ChannelEvent) -> Result<Self, Self::Error> {
+        let data = serde_json::to_string_pretty(&value)?;
+        let event = Self::default().id(value.event_id()).data(&data);
+
+        Ok(event)
+    }
 }
-- 
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