From 407ca8df6284ce1a4c649b018c7326fd195bbd26 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Fri, 13 Sep 2024 22:30:02 -0400
Subject: Support Last-Event-Id as a method of resuming channel events after a
 disconnect

---
 src/channel/routes.rs | 31 +++++++++++++++++++++++++++----
 1 file changed, 27 insertions(+), 4 deletions(-)

(limited to 'src/channel/routes.rs')

diff --git a/src/channel/routes.rs b/src/channel/routes.rs
index 0f95c69..4f83a8b 100644
--- a/src/channel/routes.rs
+++ b/src/channel/routes.rs
@@ -8,9 +8,14 @@ use axum::{
     routing::{get, post},
     Router,
 };
+use axum_extra::TypedHeader;
+use chrono::{format::SecondsFormat, DateTime};
 use futures::{future, stream::TryStreamExt as _};
 
-use super::repo::channels::Id as ChannelId;
+use super::{
+    header::LastEventId,
+    repo::{channels::Id as ChannelId, messages::BroadcastMessage},
+};
 use crate::{
     app::App, clock::RequestedAt, error::BoxedError, error::InternalError,
     login::repo::logins::Login,
@@ -61,13 +66,31 @@ async fn on_events(
     Path(channel): Path<ChannelId>,
     State(app): State<App>,
     _: Login, // requires auth, but doesn't actually care who you are
+    last_event_id: Option<TypedHeader<LastEventId>>,
 ) -> Result<impl IntoResponse, InternalError> {
+    let resume_at = last_event_id
+        .map(|TypedHeader(header)| header)
+        .map(|LastEventId(header)| header)
+        .map(|header| DateTime::parse_from_rfc3339(&header))
+        .transpose()?
+        .map(|ts| ts.to_utc());
+
     let stream = app
         .channels()
-        .events(&channel)
+        .events(&channel, resume_at.as_ref())
         .await?
-        .and_then(|msg| future::ready(serde_json::to_string(&msg).map_err(BoxedError::from)))
-        .map_ok(|msg| sse::Event::default().data(&msg));
+        .and_then(|msg| future::ready(to_event(msg)));
 
     Ok(Sse::new(stream).keep_alive(sse::KeepAlive::default()))
 }
+
+fn to_event(msg: BroadcastMessage) -> Result<sse::Event, BoxedError> {
+    let data = serde_json::to_string(&msg)?;
+    let event = sse::Event::default()
+        .id(msg
+            .sent_at
+            .to_rfc3339_opts(SecondsFormat::AutoSi, /* use_z */ true))
+        .data(&data);
+
+    Ok(event)
+}
-- 
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