Prevent sending messages to deleted channels.

I've opted to make it clear in the error message which scenario - deleted vs. non-existant - a channel falls into. This isn't particularly consistent with the rest of the API, so we might need to review this decision later, but it's at least relatively harmless if it's mistaken. (Formally, they're both 404s, so clients that go by error code won't notice.)

2 files changed, 14 insertions, 9 deletions

diff --git a/src/message/app.rs b/src/message/app.rs
index 3c74628..9792c8f 100644
--- a/src/message/app.rs
+++ b/src/message/app.rs
@@ -29,13 +29,17 @@ impl<'a> Messages<'a> {
         sent_at: &DateTime,
         body: &Body,
     ) -> Result<Message, SendError> {
+        let to_not_found = || SendError::ChannelNotFound(channel.clone());
+        let to_deleted = || SendError::ChannelDeleted(channel.clone());
+
         let mut tx = self.db.begin().await?;
-        let channel = tx
-            .channels()
-            .by_id(channel)
-            .await
-            .not_found(|| SendError::ChannelNotFound(channel.clone()))?;
+        let channel = tx.channels().by_id(channel).await.not_found(to_not_found)?;
+
+        // Ordering: don't bother allocating a sequence number before we know the channel might
+        // exist.
         let sent = tx.sequence().next(sent_at).await?;
+        let channel = channel.as_of(sent).ok_or_else(to_deleted)?;
+
         let message = tx.messages().create(&channel, sender, &sent, body).await?;
         tx.commit().await?;
 
@@ -126,6 +130,8 @@ impl<'a> Messages<'a> {
 pub enum SendError {
     #[error("channel {0} not found")]
     ChannelNotFound(channel::Id),
+    #[error("channel {0} deleted")]
+    ChannelDeleted(channel::Id),
     #[error(transparent)]
     Database(#[from] sqlx::Error),
     #[error(transparent)]
diff --git a/src/message/repo.rs b/src/message/repo.rs
index 9a4f72f..e753134 100644
--- a/src/message/repo.rs
+++ b/src/message/repo.rs
@@ -2,7 +2,7 @@ use sqlx::{SqliteConnection, Transaction, sqlite::Sqlite};
 
 use super::{Body, History, Id, snapshot::Message};
 use crate::{
-    channel,
+    channel::{self, Channel},
     clock::DateTime,
     event::{Instant, Sequence},
     user::{self, User},
@@ -23,13 +23,12 @@ pub struct Messages<'t>(&'t mut SqliteConnection);
 impl Messages<'_> {
     pub async fn create(
         &mut self,
-        channel: &channel::History,
+        channel: &Channel,
         sender: &User,
         sent: &Instant,
         body: &Body,
     ) -> Result<History, sqlx::Error> {
         let id = Id::generate();
-        let channel_id = channel.id();
 
         let message = sqlx::query!(
             r#"
@@ -45,7 +44,7 @@ impl Messages<'_> {
                     body as "body: Body"
             "#,
             id,
-            channel_id,
+            channel.id,
             sender.id,
             sent.at,
             sent.sequence,