iotaledger / iota / 26136038453

67%

Build Type

push

github

Committed by web-flow

Commit Message

feat(consensus): Starfish hardening (#11529)

# Description of change

Bounds the size of a starfish block header to `O(committee_size)` and
adds the supporting machinery needed to keep that bound workable in
steady state. All new behavior is gated behind the
`consensus_block_restrictions` protocol-config feature flag, enabled at
protocol version 27 for Testnet/Devnet; Mainnet is unaffected.

A pre-hardening block header carried three open-ended collections that
could grow over time: acknowledgments, commit votes, and ancestor refs
through GC. The hardening makes each of them bounded both at the
verifier (rejecting non-conforming blocks) and at the proposer (capping
what it emits), and adds two pieces of state hygiene so the proposer
never accumulates more than what it is allowed to send.

### Constant-size block header

- **#11382 — bound acknowledgments and verify ancestor/ack round-gap.**
Caps acknowledgments per block at `2 * committee_size`. Verifies that
every acknowledgment and every non-own ancestor falls in the window
`[block.round - gc_depth, block.round)`, with `block_verifier` rejecting
`TooManyAcknowledgments`, `InvalidAcknowledgmentRound`,
`AcknowledgmentRoundTooOld`, `AncestorRoundTooOld`.
- **#11383 — bound block commit votes.** Caps commit votes per block at
`committee_size` (was a hardcoded 100). `take_commit_votes` and
`block_verifier` are switched to the new
`ProtocolConfig::max_commit_votes_per_block(committee_size)`; over-quota
blocks fail verification with `TooManyCommitVotes`.

Together these two pin every variable-size field on the header to
`O(committee_size)`. Concretely, the optimistic steady-state size
(`references = N` with full ancestor/ack overlap, `commit_votes = 1`) is
**unchanged** by this PR — about **2.4 KB at N=60 and 3.9 KB at N=100**
(`≈ 37·N + 186` bytes) — while the worst case is now **bounded** at
roughly **9 KB and 15 KB** respectively (`≈ 147·N + 150` bytes: up to
`3N` `BlockRef`s of 37 B in the merged ance... (continued)

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