stream: fix a snapshot cache bug

Previously a snapshot created as part of a resumse-stream request could have incorrectly
cached the newSnapshotToFollow event. This would cause clients to error because they
received an unexpected framing event.
This commit is contained in:
Daniel Nephin 2021-02-16 12:20:19 -05:00
parent 2726c65fbe
commit a29b848e3b
2 changed files with 21 additions and 18 deletions

4
.changelog/9772.txt Normal file
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@ -0,0 +1,4 @@
```release-note:bug
streaming: fixes a bug caused by caching an incorrect snapshot, that would cause clients
to error until the cache expired.
```

View File

@ -176,28 +176,27 @@ func (e *EventPublisher) Subscribe(req *SubscribeRequest) (*Subscription, error)
}
snapFromCache := e.getCachedSnapshotLocked(req)
if req.Index == 0 && snapFromCache != nil {
if snapFromCache == nil {
snap := newEventSnapshot()
snap.appendAndSplice(*req, handler, topicHead)
e.setCachedSnapshotLocked(req, snap)
snapFromCache = snap
}
// If the request.Index is 0 the client has no view, send a full snapshot.
if req.Index == 0 {
return e.subscriptions.add(req, snapFromCache.First), nil
}
snap := newEventSnapshot()
// if the request has an Index the client view is stale and must be reset
// otherwise the request has an Index, the client view is stale and must be reset
// with a NewSnapshotToFollow event.
if req.Index > 0 {
snap.buffer.Append([]Event{{
Topic: req.Topic,
Payload: newSnapshotToFollow{},
}})
if snapFromCache != nil {
snap.buffer.AppendItem(snapFromCache.First)
return e.subscriptions.add(req, snap.First), nil
}
}
snap.appendAndSplice(*req, handler, topicHead)
e.setCachedSnapshotLocked(req, snap)
return e.subscriptions.add(req, snap.First), nil
result := newEventSnapshot()
result.buffer.Append([]Event{{
Topic: req.Topic,
Payload: newSnapshotToFollow{},
}})
result.buffer.AppendItem(snapFromCache.First)
return e.subscriptions.add(req, result.First), nil
}
func (s *subscriptions) add(req *SubscribeRequest, head *bufferItem) *Subscription {