feat: added silent mode, error subscriber

[petruki]

This pull request introduces comprehensive support for "silent mode" fallback in the client, allowing the SDK to automatically switch to local evaluation when remote requests fail, and to recover when the remote service becomes healthy again. It also adds a thread-safe error notification subscription mechanism, and includes extensive tests for silent mode behavior. Several code refactorings separate snapshot and silent mode logic for clarity and maintainability.

Silent mode fallback and recovery:

• Adds a new client_silent_mode.go file implementing logic for detecting when to use silent mode, updating and clearing the silent mode token, and checking remote health to restore normal operation. The Switcher now uses this logic to transparently fall back to local evaluation and recover when possible. [1] [2] [3] [4]

Error notification subscription:

• Introduces a thread-safe SubscribeNotifyError mechanism to allow clients to register a callback for remote errors, both globally and per-client. This enables applications to be notified when the SDK falls back to silent mode due to remote errors. [1] [2] [3]

Testing and reliability:

• Adds client_silent_mode_test.go with thorough tests covering fallback, error notification, recovery, and edge cases where no snapshot is available.

Code organization and refactoring:

• Moves snapshot-related concurrency logic to a new client_snapshot.go file for better separation of concerns and maintainability.

Documentation update:

• Updates the README.md to clarify how remote connect timeouts affect silent mode fallback responsiveness.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud