fix: Circuit-breaker for Code Suggestions (Web IDE)

When receiving sequential error responses from the code suggestions API, lower the frequency of API requests while user types. After 4 sequential error responses, the code completions provider will only send a fetch completions HTTP request every 10 seconds. Every subsequent HTTP request will double the waiting time before another request is fired.

How does it work?

A CircuitBreaker class tracks the number of HTTP request failures. When it counts 4 subsequent requests, it marks itself as "breaking" and it unmarks itself after X ms. GitLabCodeCompletionProvider uses this state to decide if it should continue sending API requests or not.

How to test in your local environment

• Follow these instructions to test code suggestions in your local environment: https://gitlab.com/gitlab-org/gitlab-web-ide/-/blob/main/docs/dev/code-suggestions.md#ai-assisted-code-suggestions
• Change the following line in the code-suggestions-proxy project to return a 500 error https://gitlab.com/a_akgun/code-suggestions-proxy/-/blob/main/server.js#L32.
• In the Web IDE, start typing to get code suggestions. You should see that, with every error response, the fetch completions requests should happen less often.

Related gitlab#412326 (closed)