chore: don't try to prune empty redis stream

libs/collab-stream/src/client.rs

@@ -167,14 +167,18 @@ impl CollabRedisStream {
       .into_iter()
       .map(|stream_id| stream_id.id)
       .collect();
-    let count: usize = conn.xdel(stream_key, &msg_ids).await?;
-    drop(conn);
-    tracing::debug!(
-      "Pruned redis stream `{}` <= `{}` ({} objects)",
-      stream_key,
-      message_id,
-      count
-    );
-    Ok(count)
+    if !msg_ids.is_empty() {
+      let count: usize = conn.xdel(stream_key, &msg_ids).await?;
+      drop(conn);
+      tracing::debug!(
+        "Pruned redis stream `{}` <= `{}` ({} objects)",
+        stream_key,
+        message_id,
+        count
+      );
+      Ok(count)
+    } else {
+      Ok(0)
+    }
   }
 }

services/appflowy-collaborate/src/group/group_init.rs

@@ -612,26 +612,34 @@ impl CollabGroup {
     if let Ok(sv) = state.state_vector.try_read() {
       // we optimistically try to obtain state vector lock for a fast track:
       // if we remote sv is up-to-date with current one, we don't need to do anything
-      if remote_sv == &*sv {
-        tracing::trace!("remote client is up to date - nothing to send");
-        return Ok(None);
+      match sv.partial_cmp(&remote_sv) {
+        Some(std::cmp::Ordering::Equal) => return Ok(None), // client and server are in sync
+        Some(std::cmp::Ordering::Less) => {
+          // server is behind client
+          let msg = Message::Sync(SyncMessage::SyncStep1(sv.clone()));
+          return Ok(Some(msg.encode_v1()));
+        },
+        Some(std::cmp::Ordering::Greater) | None => { /* server has some new updates */ },
       }
     }
 
+    // we need to reconstruct document state on the server side
     let snapshot = state
       .persister
       .load()
       .await
       .map_err(|err| RTProtocolError::Internal(err.into()))?;
+
+    // prepare document state update and state vector
     let tx = snapshot.collab.transact();
     let doc_state = tx.encode_state_as_update_v1(remote_sv);
     let local_sv = tx.state_vector();
     drop(tx);
+
     // Retrieve the latest document state from the client after they return online from offline editing.
     tracing::trace!("sending missing data to client ({} bytes)", doc_state.len());
     let mut encoder = EncoderV1::new();
     Message::Sync(SyncMessage::SyncStep2(doc_state)).encode(&mut encoder);
-
     //FIXME: this should never happen as response to sync step 1 from the client, but rather be
     //  send when a connection is established
     Message::Sync(SyncMessage::SyncStep1(local_sv)).encode(&mut encoder);