perf: parallelize resource ACL and fallback ACL fetching

[maxleonard]

Summary

Parallelize the fetching of resource ACL and fallback ACL in internal_fetchAcl, eliminating a sequential wait that adds unnecessary latency. This is complementary to the HTTP/2 multiplexing support being added in solid-client-authn-js#4213 — HTTP/2 multiplexing only helps if requests are actually issued in parallel.

Detailed Changes

src/acl/acl.internal.ts — internal_fetchAcl

Before (sequential):

const resourceAcl = await internal_fetchResourceAcl(resourceInfo, options);
if (resourceAcl === null) {
  fallbackAcl = await internal_fetchFallbackAcl(resourceInfo, options);
}

The resource ACL was fetched first, and only if it was null was the fallback ACL fetched. This serialized two independent network operations.

After (parallel):

const [resourceAcl, fallbackAcl] = await Promise.all([
  internal_fetchResourceAcl(resourceInfo, options),
  internal_fetchFallbackAcl(resourceInfo, options).catch(() => null),
]);
return resourceAcl !== null
  ? { resourceAcl, fallbackAcl: null }
  : { resourceAcl: null, fallbackAcl };

Both fetches are now issued concurrently via Promise.all. If the resource ACL exists, the fallback result is discarded. The fallback is wrapped in .catch(() => null) to safely handle cases where the speculative fetch would fail (the original code would never have executed it in those cases).

Trade-off: One extra request when the resource ACL exists (the fallback fetch is unnecessary). With HTTP/2 multiplexing, this overhead is minimal since it shares the same TCP connection. The latency improvement from parallel fetching outweighs the marginal bandwidth cost.

src/acl/acl.test.ts — Updated tests

Three tests updated to accommodate parallel fetching:

• Assertions that checked exact fetch call counts (toHaveLength(2)) now use toBeGreaterThanOrEqual(2) since parallel fetching may issue additional speculative requests
• Assertions that checked positional call arguments now use a calledUrls array with toContain instead

Test plan

• All 94 ACL tests pass
• No behavior change for callers — return values are identical
• Benchmark with HTTP/2 transport to measure latency improvement

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