How to listen to firestore through RPC - firebase

Question

I want to listen to real time changes in firestore and I am also only allowed to use Go. Since firestore SDK for Go doesn't have any option to listen for real time changes, I decided to use the firestore v1beta1 sdk.
I have written the following code to do that
func TestRPCHandler(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
c, err := firestore.NewClient(context.Background())
databaseName := "projects/[project_name]/databases/(default)"
if err != nil {
panic(err)
}
stream, err := client.Listen(context.Background())
if err != nil {
panic(err)
}
request := &firestorepb.ListenRequest{
Database: databaseName,
TargetChange: &firestorepb.ListenRequest_AddTarget{
AddTarget: &firestorepb.Target{
TargetType: &firestorepb.Target_Documents{
Documents: &firestorepb.Target_DocumentsTarget{
Documents: []string{"projects/[project_name]/databases/(default)/[collection_name]"} ,
},
},
},
},
}
if err := stream.Send(request); err != nil {
panic(err)
}
if err := stream.CloseSend(); err != nil {
panic(err)
}
for {
resp, err := stream.Recv()
if err == io.EOF {
break
}
if err != nil {
panic(err)
}
}
}
When I am doing this, the code does not detect any changes I bring about manually in the database. stream.Recv() just returns EOF and exits immediately. I even tried manually waiting by adding time.Sleep() but that does not help either.

Answer 1

You don't need the beta SDK or hacks to make this happen, I found the solution, it's pretty easy actually.
The https://firebase.google.com/docs/firestore/query-data/listen documentation does not contain an example for Go.
The source code of the firestore client API for Go has an unexported watchStream which we cannot directly use: https://github.com/googleapis/google-cloud-go/blob/master/firestore/watch.go#L130
Deep search of the repository shows that this is actually used on the DocumentSnapshotIterator and QuerySnapshotIterator at: https://github.com/googleapis/google-cloud-go/blob/master/firestore/docref.go#L644 and: https://github.com/googleapis/google-cloud-go/blob/master/firestore/query.go#L716.
The Collection contains a Snapshots method which returns the snapshot iterator that we want, after that all is easy, we just make an infivitive loop through its Next method.
Example:
cols, err := client.Collections(context.Background()).GetAll()
for _, col := range cols {
iter := col.Snapshots(context.Background())
defer iter.Stop()
for {
doc, err := iter.Next()
if err != nil {
if err == iterator.Done {
break
}
return err
}
for _, change := range doc.Changes {
// access the change.Doc returns the Document,
// which contains Data() and DataTo(&p) methods.
switch change.Kind {
case firestore.DocumentAdded:
// on added it returns the existing ones.
isNew := change.Doc.CreateTime.After(l.startTime)
// [...]
case firestore.DocumentModified:
// [...]
case firestore.DocumentRemoved:
// [...]
}
}
}
}
Yours, Gerasimos Maropoulos aka #kataras

Answer 2

Firebase's Get realtime updates with Cloud Firestore documentation currently indicates that Go is not yet supported.
// Not yet supported in Go client library