Chunk FindMissingBlobsRequest appropriately

[tgolsson]

Fixes #20674

[jasonwbarnett]

I haven't forgotten about this @tgolsson. I just haven't made time to test this. I'll attempt to get to this no later than end of next week (4/14/2024).

[jasonwbarnett]

@tgolsson it worked!

[huonw]

Nice

[huonw]

Thanks for the test. I think there's a few plausible mistakes that we could introduce in future that won't be caught:

1. only sending each unique digest once, thus invalidating this test (i.e. if we do the HashSet idea, the list_missing_digests will be working with just one digest and thus only send one request)
2. skipping the second+ request (either not sending them at all, or not including the results in the final aggregation)
3. Not sure about this one: if we break this in another way and start sending >4MiB requests, does the StubCAS reject the requests (i.e. does this test fail without the fix)?

I think we can address each of them:

1. check assert_eq!(cas.request_count(RequestType::CASFindMissingBlobs), 2) so that the test starts failing if that core assumption changes
2. add two digests that is missing, within each "chunk" (e.g. one at the start and one at the end)
3. add request size enforcement to StubCAS if not already there (this might cause other tests to fail, so we might want it to be optional until we resolve them)

[tgolsson]

add request size enforcement to StubCAS if not already there (this might cause other tests to fail, so we might want it to be optional until we resolve them

If I remove my fix, the existing test fails.

assertion `left == right` failed
  left: Err("OutOfRange: \"Error, decoded message length too large: found 7000000 bytes, the limit is: 4194304 bytes\"")
 right: Ok({})

[huonw]

Oh, also, does this fix #20674? Could you update the PR description like "fixes #20674" to have the appropriate auto-close behaviour. Thanks!

[huonw]

We've just branched for 2.22, so merging this pull request now will come out in 2.23, please move the release notes updates to docs/notes/2.23.x.md. Thank you!

[huonw]

We've just branched for 2.23, so merging this pull request now will come out in 2.24, please move the release notes updates to docs/notes/2.24.x.md. Thank you!

[cburroughs]

I think from the comments this is >90% of the way there and fixes a bug. @tgolsson would you mind dusting it off?

[huonw]

(We're now up to docs/notes/2.26.x.md for release notes.)

[huonw]

Really nice, thanks for revisiting it!

[huonw]

(I've edited the Github magic auto-closing incantation of "Fixes #20674" into the PR description, but feel free to revise if that's not correct.)

[WorkerPants]

I was unable to cherry-pick this PR; the milestone seems to be missing.

@tgolsson: Please add the milestone to the PR and re-run the Auto Cherry-Picker job using the "Run workflow" button.

🤖 Beep Boop here's my run link