[broadcast] Use BTreeMap in buffered::Engine

[clabby]

Overview

Swaps the map type in buffered::Engine from HashMap to BTreeMap. This change makes the iteration over values returned by buffered::Mailbox::get deterministically ordered.

I ran into this causing issues in broadcast order over in #1680.

monorepo/broadcast/src/buffered/engine.rs

Lines 239 to 279 in b835347

	/// Searches through all maintained messages for a match.
	fn find_messages(
	&mut self,
	peer: &Option<P>,
	commitment: M::Commitment,
	digest: Option<M::Digest>,
	all: bool,
	) -> Vec<M> {
	match peer {
	// Only consider messages from the peer filter
	Some(s) => self
	.deques
	.get(s)
	.into_iter()
	.flat_map(|dq| dq.iter())
	.filter(|pair| pair.commitment == commitment)
	.filter_map(|pair| {
	self.items
	.get(&pair.commitment)
	.and_then(|m| m.get(&pair.digest))
	})
	.cloned()
	.collect(),
	// Search by commitment
	None => match self.items.get(&commitment) {
	// If there are no messages for the commitment, return an empty vector
	None => Vec::new(),
	// If there are messages, return the ones that match the digest filter
	Some(msgs) => match digest {
	// If a digest is provided, return whatever matches it.
	Some(dg) => msgs.get(&dg).cloned().into_iter().collect(),
	// If no digest was provided, return `all` messages for the commitment.
	None if all => msgs.values().cloned().collect(),
	None => msgs.values().next().cloned().into_iter().collect(),
	},
	},
	}
	}

[patrick-ogrady]

Normally, we'd also add some regression test for a case like this? Refer to consensus for some examples of this (run a test on the same seed twice and assert the "Auditor State" is identical).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.20%. Comparing base (a0d076b) to head (4bfcbf2).
⚠️ Report is 3 commits behind head on main.

@@           Coverage Diff            @@
##             main    #1687    +/-   ##
========================================
  Coverage   92.20%   92.20%            
========================================
  Files         294      296     +2     
  Lines       75325    75557   +232     
========================================
+ Hits        69456    69670   +214     
- Misses       5869     5887    +18     

Files with missing lines	Coverage Δ
broadcast/src/buffered/engine.rs	92.76% <100.00%> (ø)
broadcast/src/buffered/mod.rs	99.55% <100.00%> (+0.03%)	⬆️

... and 5 files with indirect coverage changes

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