useCallableFunctionResponse invokes the cloud function on every re-render

[tyler-reitz]

Problem

useCallableFunctionResponse constructs its observable source eagerly via rxfire's httpsCallable, which invokes the cloud function at hook-render time. Every re-render that doesn't hit the observable cache fires a real cloud function call that is then discarded.

Unlike useIdTokenResult (which wastes a network read), this has a write-side effect: the function executes and bills against quota on every render cycle.

Fix

Wrap in defer() so the function is invoked at subscription time, not render time:

const observable$ = defer(() => httpsCallable(functionRef, data, options));

Related

• fix: surface observable errors via status instead of re-throwing #735 fixed the same pattern in useStorageDownloadURL
• useIdTokenResult fires a redundant token fetch on every re-render #743 tracks the same issue in useIdTokenResult