Updates from review and from testing.

sqlx-core/src/postgres/listen.rs

@@ -1,3 +1,5 @@
+use std::ops::DerefMut;
+
 use futures_core::future::BoxFuture;
 use futures_core::stream::BoxStream;
 
@@ -15,9 +17,9 @@ impl PgConnection {
     /// Register this connection as a listener on the specified channel.
     ///
     /// If an error is returned here, the connection will be dropped.
-    pub async fn listen(mut self, channel: &impl AsRef<str>) -> Result<PgListener<Self>> {
-        let cmd = format!(r#"LISTEN "{}""#, channel.as_ref());
-        let _ = self.execute(cmd.as_str(), Default::default()).await?;
+    pub async fn listen(mut self, channel: impl AsRef<str>) -> Result<PgListener<Self>> {
+        let cmd = build_listen_all_query(&[channel]);
+        let _ = self.send(cmd.as_str()).await?;
         Ok(PgListener::new(self))
     }
 
@@ -28,25 +30,18 @@ impl PgConnection {
         mut self,
         channels: impl IntoIterator<Item = impl AsRef<str>>,
     ) -> Result<PgListener<Self>> {
-        for channel in channels {
-            let cmd = format!(r#"LISTEN "{}""#, channel.as_ref());
-            let _ = self.execute(cmd.as_str(), Default::default()).await?;
-        }
+        let cmd = build_listen_all_query(channels);
+        let _ = self.send(cmd.as_str()).await?;
         Ok(PgListener::new(self))
     }
-
-    /// Build a LISTEN query based on the given channel input.
-    fn build_listen_query(channel: &impl AsRef<str>) -> String {
-        format!(r#"LISTEN "{}";"#, channel.as_ref())
-    }
 }
 
 impl PgPool {
     /// Fetch a new connection from the pool and register it as a listener on the specified channel.
-    pub async fn listen(&self, channel: &impl AsRef<str>) -> Result<PgListener<PgPoolConnection>> {
+    pub async fn listen(&self, channel: impl AsRef<str>) -> Result<PgListener<PgPoolConnection>> {
         let mut conn = self.acquire().await?;
-        let cmd = PgConnection::build_listen_query(channel);
-        let _ = conn.execute(cmd.as_str(), Default::default()).await?;
+        let cmd = build_listen_all_query(&[channel]);
+        let _ = conn.send(cmd.as_str()).await?;
         Ok(PgListener::new(conn))
     }
 
@@ -56,31 +51,31 @@ impl PgPool {
         channels: impl IntoIterator<Item = impl AsRef<str>>,
     ) -> Result<PgListener<PgPoolConnection>> {
         let mut conn = self.acquire().await?;
-        for channel in channels {
-            let cmd = PgConnection::build_listen_query(&channel);
-            let _ = conn.execute(cmd.as_str(), Default::default()).await?;
-        }
+        let cmd = build_listen_all_query(channels);
+        let _ = conn.send(cmd.as_str()).await?;
         Ok(PgListener::new(conn))
     }
 }
 
 impl PgPoolConnection {
-    /// Fetch a new connection from the pool and register it as a listener on the specified channel.
-    pub async fn listen(mut self, channel: &impl AsRef<str>) -> Result<PgListener<Self>> {
-        let cmd = PgConnection::build_listen_query(channel);
-        let _ = self.execute(cmd.as_str(), Default::default()).await?;
+    /// Register this connection as a listener on the specified channel.
+    ///
+    /// If an error is returned here, the connection will be dropped.
+    pub async fn listen(mut self, channel: impl AsRef<str>) -> Result<PgListener<Self>> {
+        let cmd = build_listen_all_query(&[channel]);
+        let _ = self.send(cmd.as_str()).await?;
         Ok(PgListener::new(self))
     }
 
-    /// Fetch a new connection from the pool and register it as a listener on the specified channels.
+    /// Register this connection as a listener on all of the specified channels.
+    ///
+    /// If an error is returned here, the connection will be dropped.
     pub async fn listen_all(
         mut self,
         channels: impl IntoIterator<Item = impl AsRef<str>>,
     ) -> Result<PgListener<Self>> {
-        for channel in channels {
-            let cmd = PgConnection::build_listen_query(&channel);
-            let _ = self.execute(cmd.as_str(), Default::default()).await?;
-        }
+        let cmd = build_listen_all_query(channels);
+        let _ = self.send(cmd.as_str()).await?;
         Ok(PgListener::new(self))
     }
 }
@@ -99,16 +94,15 @@ impl<C> PgListener<C> {
 
 impl<C> PgListener<C>
 where
-    C: AsMut<PgConnection>,
+    C: DerefMut<Target=PgConnection>,
 {
     /// Get the next async notification from the database.
     pub async fn next(&mut self) -> Result<NotifyMessage> {
         loop {
-            match self.0.as_mut().receive().await? {
+            match (&mut self.0).receive().await? {
                 Some(Message::NotificationResponse(notification)) => return Ok(notification.into()),
-                // TODO: verify with team if this is correct. Looks like the connection being closed will cause an error
-                // to propagate up from `recevie`, but it would be good to verify with team.
-                Some(_) | None => continue,
+                Some(msg) => return Err(protocol_err!("unexpected message received from database {:?}", msg).into()),
+                None => continue,
             }
         }
     }
@@ -170,6 +164,7 @@ impl<C: Connection<Database = Postgres>> crate::Executor for PgListener<C> {
 }
 
 /// An asynchronous message sent from the database.
+#[derive(Debug)]
 #[non_exhaustive]
 pub struct NotifyMessage {
     /// The channel of the notification, which can be thought of as a topic.
@@ -186,3 +181,30 @@ impl From<Box<NotificationResponse>> for NotifyMessage {
         }
     }
 }
+
+/// Build a query which issues a LISTEN command for each given channel.
+fn build_listen_all_query(channels: impl IntoIterator<Item = impl AsRef<str>>) -> String {
+    channels.into_iter().fold(String::new(), |mut acc, chan| {
+        acc.push_str(r#"LISTEN ""#);
+        acc.push_str(chan.as_ref());
+        acc.push_str(r#"";"#);
+        acc
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn build_listen_all_query_with_single_channel() {
+        let output = build_listen_all_query(&["test"]);
+        assert_eq!(output.as_str(), r#"LISTEN "test";"#);
+    }
+
+    #[test]
+    fn build_listen_all_query_with_multiple_channels() {
+        let output = build_listen_all_query(&["channel.0", "channel.1"]);
+        assert_eq!(output.as_str(), r#"LISTEN "channel.0";LISTEN "channel.1";"#);
+    }
+}