fix: Enhance error logs in store's Watch func

[leakonvalinka]

This PR

• improves errror logs in the store's Watch function

Related Issues

#1863

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[gemini-code-assist]

Summary of Changes

Hello @leakonvalinka, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on improving the diagnostic capabilities of the store's Watch function by enhancing its error logging. The changes ensure that error messages related to flag watching include specific selector information, making it significantly easier to understand the context of failures and debug issues more efficiently.

Highlights

• Enhanced Error Logging: Introduced a selectorString variable to capture and format details of the selector being used in the Watch function.
• Improved Error Context: Modified error messages within the Watch function to include the selectorString, providing more specific context when errors occur during flag retrieval or context-based watching.

Changelog

• core/pkg/store/store.go
  • Added logic to extract and format selector details into a selectorString for use in error messages.
  • Updated the error log message for s.selectOrAll(selector) failures to include the newly formatted selectorString.
  • Updated the error log message for ws.WatchCtx(ctx) failures to include the selectorString for better context.

Activity

• No human activity (comments, reviews) has been recorded on this pull request yet.

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[gemini-code-assist]

Code Review

This pull request enhances error logging in the Watch function by including selector information. The change is a good improvement for debuggability. I've added one suggestion to make the selector string generation more robust by handling selectors with multiple constraints, which will prevent potentially misleading log messages.

[aepfli]

The changes are simple and nice, some questions and suggestions from my side added. especially i think we should extract the generation of the string into an own method.

[toddbaert]

I think the reason this came up is because some client's like us internally use stream deadlines. Stream deadlines are sent from the client, but enforced both on the client and on the server. This error will fire when the context deadline is exceeded, which is perfectly expected in our case. You can test this by connecting a client with a 10s stream deadline to flagd, and you will see this basically every 10s, I think.

We may want to log this as debug if the error is a deadline exceeded.

EDIT:

You can do this with grpcurl

grpcurl -max-time 10   -plaintext   -import-path "$PROTO_DIR" -proto flagd/sync/v1/sync.proto   -d '{"selector": "flagSetId=app-flags"}'   localhost:8015   flagd.sync.v1.FlagSyncService/SyncFlags

10s later:

2026-02-05T07:46:04.414-0500    error   store/store.go:329      error watching flags: context canceled
github.com/open-feature/flagd/core/pkg/store.(*Store).Watch.func1
        /home/todd/git/flagd/core/pkg/store/store.go:329

[leakonvalinka]

If we go from log level error to debug, it might take users longer to notice the logs. If this is a transitive error then that's fine I think, but if it requires user/client action it would be good to have some error log. I'm not 100% grasping what the error is about so if that doesn't make sense forget about it :D

[toddbaert]

If we go from log level error to debug, it might take users longer to notice the logs. If this is a transitive error then that's fine I think, but if it requires user/client action it would be good to have some error log. I'm not 100% grasping what the error is about so if that doesn't make sense forget about it :D

Basically, if the error is one of these types, it's not an error: ctx.Err() == context.DeadlineExceeded || ctx.Err() == context.Canceled, it's totally expected behavior because either the client has disconnected cleanly (maybe the client is shutting down) or the client's deadline is up.

Other errors are really unexpected, but these are not (not every ergonomic, I know).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud