714: Show error is we fail to reset defences

[calummcgowan]

Description

• When running the frontend only, attempting to 'reset' any of the defence configurations will result in an error message being displaying in the chat.
• Fixes Show error if we fail to reset defences #714

Screenshots

Notes

• Changes made to MainComponent.tsx: add chat message when resetDefence fails
• Changes to defenceService.ts: return null when DefenceResetResponse promise fails

Concerns

• No unit tests added - may be irrelevant due to running only frontend

Checklist

Have you done the following?

• Linked the relevant Issue
• [] Added tests
• Ensured the workflow steps are passing

[chriswilty]

Sorry it took a while to get around to a review.

This does the job, thank you! I have a small request for a minor enhancement, and another to use async/await instead of a promise chain.

[chriswilty]

We have a mix of promises and async/awaits here. Prefer async/await wherever possible (and here it is possible).

Note that fetch does not throw an error for non-200 status codes, so this will fail when the service (legitimately) returns text/plain error messages, as the body then is not JSON. I appreciate that a) that was already happening, and b) the acceptance criteria specified only what should happen when the server is unavailable (which does indeed result in an error thrown) but we have the opportunity to make this more robust if we check for response.ok ...

As this project is so infrequently updated, may I ask for a little more from you? Firstly, use async/await and try/catch for consistency, and secondly, could you check for response.ok and if false, then console.warn the response text (and then return null)?