From 2b4cf5c62ff82fa408a4f82bde0b561ff3b15497 Mon Sep 17 00:00:00 2001
From: Owen Jacobson <owen@grimoire.ca>
Date: Wed, 18 Sep 2024 02:22:09 -0400
Subject: Make BoxedError an implementation detail of InternalError.

---
 src/channel/app.rs | 44 +++++++++++++++++++++++++++++++-------------
 1 file changed, 31 insertions(+), 13 deletions(-)

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

diff --git a/src/channel/app.rs b/src/channel/app.rs
index e72564d..0a28fb6 100644
--- a/src/channel/app.rs
+++ b/src/channel/app.rs
@@ -3,17 +3,16 @@ use std::sync::{Arc, Mutex, MutexGuard};
 
 use futures::{
     future,
-    stream::{self, StreamExt as _, TryStreamExt as _},
+    stream::{self, StreamExt as _},
     Stream,
 };
 use sqlx::sqlite::SqlitePool;
 use tokio::sync::broadcast::{channel, Sender};
-use tokio_stream::wrappers::BroadcastStream;
+use tokio_stream::wrappers::{errors::BroadcastStreamRecvError, BroadcastStream};
 
 use super::repo::broadcast::{self, Provider as _};
 use crate::{
     clock::DateTime,
-    error::BoxedError,
     repo::{
         channel::{self, Channel, Provider as _},
         error::NotFound as _,
@@ -75,17 +74,16 @@ impl<'a> Channels<'a> {
         &self,
         channel: &channel::Id,
         resume_at: Option<&DateTime>,
-    ) -> Result<impl Stream<Item = Result<broadcast::Message, BoxedError>> + 'static, EventsError>
-    {
-        fn skip_stale<E>(
+    ) -> Result<impl Stream<Item = broadcast::Message> + 'static, EventsError> {
+        fn skip_stale(
             resume_at: Option<&DateTime>,
-        ) -> impl for<'m> FnMut(&'m broadcast::Message) -> future::Ready<Result<bool, E>> {
+        ) -> impl for<'m> FnMut(&'m broadcast::Message) -> future::Ready<bool> {
             let resume_at = resume_at.cloned();
             move |msg| {
-                future::ready(Ok(match resume_at {
+                future::ready(match resume_at {
                     None => false,
                     Some(resume_at) => msg.sent_at <= resume_at,
-                }))
+                })
             }
         }
         let mut tx = self
@@ -98,13 +96,12 @@ impl<'a> Channels<'a> {
         let live_messages = self
             .broadcaster
             .listen(&channel.id)
-            .map_err(BoxedError::from)
-            .try_skip_while(skip_stale(resume_at));
+            .skip_while(skip_stale(resume_at));
 
         let stored_messages = tx.broadcast().replay(&channel, resume_at).await?;
         tx.commit().await?;
 
-        let stored_messages = stream::iter(stored_messages).map(Ok);
+        let stored_messages = stream::iter(stored_messages);
 
         Ok(stored_messages.chain(live_messages))
     }
@@ -176,15 +173,36 @@ impl Broadcaster {
         // there are no receivers. In this use case, that's fine; a lack of
         // listening consumers (chat clients) when a message is sent isn't an
         // error.
+        //
+        // The successful return value, which includes the number of active
+        // receivers, also isn't that interesting to us.
         let _ = tx.send(message);
     }
 
     // panic: if ``channel`` has not been previously registered, and was not
     // part of the initial set of channels.
-    pub fn listen(&self, channel: &channel::Id) -> BroadcastStream<broadcast::Message> {
+    pub fn listen(&self, channel: &channel::Id) -> impl Stream<Item = broadcast::Message> {
         let rx = self.sender(channel).subscribe();
 
         BroadcastStream::from(rx)
+            .take_while(|r| {
+                future::ready(match r {
+                    Ok(_) => true,
+                    // Stop the stream here. This will disconnect SSE clients
+                    // (see `routes.rs`), who will then resume from
+                    // `Last-Event-ID`, allowing them to catch up by reading
+                    // the skipped messages from the database.
+                    Err(BroadcastStreamRecvError::Lagged(_)) => false,
+                })
+            })
+            .map(|r| {
+                // Since the previous transform stops at the first error, this
+                // should always hold.
+                //
+                // See also <https://users.rust-lang.org/t/taking-from-stream-while-ok/48854>.
+                debug_assert!(r.is_ok());
+                r.unwrap()
+            })
     }
 
     // panic: if ``channel`` has not been previously registered, and was not
-- 
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