feature(rpc): Add basic long polling support to the getblocktemplate RPC

[teor2345]

Motivation

This PR implements basic long polling support, checking for changes by re-fetching from the sync status, state and mempool.

Part of ticket #5720.

Complex Code or Requirements

We need to hold the RPC request open until the response will change. This means running a loop and a select!{} in a future.

Solution

Implement inefficient long polling by checking the state/mempool/syncer, waiting 5 seconds, then checking it again. Also wait for the max time.

Related changes:

• Change impl From<LongPollInput> for LongPollId into a named method
• Rename the long_poll_id field
• Cleanup some comments

Review

This is ready for review, I'm doing some manual testing now. Automated testing will happen in the next PR.

Efficiency and refactors are out of scope for this PR, I'd like to focus on getting some kind of working implementation merged.

Reviewer Checklist

• Will the PR name make sense to users?
  • Does it need extra CHANGELOG info? (new features, breaking changes, large changes)
• Are the PR labels correct?
• Does the code do what the ticket and PR says?
  • Does it change concurrent code, unsafe code, or consensus rules?
• How do you know it works? Does it have tests?

Follow Up Work

• medium priority: check for state changes efficiently
• low priority: check for sync status and mempool changes efficiently

[codecov]

Codecov Report

Merging #5843 (5d1bba2) into main (e9d6e97) will decrease coverage by 0.04%.
The diff coverage is n/a.

❗ Current head 5d1bba2 differs from pull request most recent head 99f244f. Consider uploading reports for the commit 99f244f to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5843      +/-   ##
==========================================
- Coverage   78.48%   78.44%   -0.05%     
==========================================
  Files         308      308              
  Lines       38706    38706              
==========================================
- Hits        30379    30361      -18     
- Misses       8327     8345      +18     

[teor2345]

This is ready for review, I'm doing some manual testing now. Automated testing will happen in the next PR.

[teor2345]

A bunch of google cloud jobs seemed to have failed setup with:

ssh: connect to host 104.198.199.90 port 22: Connection timed out

https://github.com/ZcashFoundation/zebra/actions/runs/3689513976/jobs/6246166936#step:11:78

[teor2345]

@Mergifyio update

[mergify]

update

✅ Branch has been successfully updated

[arya2]

This looks like it should work.

[teor2345]

@arya2 just checking why you marked this PR as "do-not-merge"?

It would be easier for me if this was part of the main branch and I didn't have to rebase my changes for PR #5862.

I'm also happy to sort out tests and any fixes in the next PR.

[oxarbitrage]

I think is in case someone else wanted to review as @dconnolly is in the list as well.

[oxarbitrage]

I think is in case someone else wanted to review as @dconnolly is in the list as well.

But i think one approval is ok here so we can just remove the do not merge tag.

[arya2]

@arya2 just checking why you marked this PR as "do-not-merge"?

Just in case we wanted a second reviewer. I'll remove the label.

[teor2345]

@arya2 just checking why you marked this PR as "do-not-merge"?

Just in case we wanted a second reviewer. I'll remove the label.

Always happy to get a second review, but I try not to block unless someone has committed to doing a review soon.