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Adds snap/2 capability advertisement, GetBlockAccessLists (0x08) / BlockAccessLists (0x09) message types with version-aware Message dispatch, BAL storage API, and BAL persistence in all block-import paths. snap/1 remains supported. No server/client/healing logic yet; those land in the next run.
Adds the GetBlockAccessLists server responder with a 2 MiB cumulative soft cap, the client request method that returns the serving peer id for accurate failure attribution, the apply_bal / advance_state_via_bals replay engine with strict in-order application and per-block hash verification, and the snap_sync state machine branch that uses BAL replay under snap/2 with a final state-root check, falling back to snap/1 trie healing otherwise.
Adds server-side unit tests for process_block_access_lists_request (empty / known / mixed / size-cap / snap/1 dispatch rejection), two more apply_bal cases (pre-state-gap fresh storage slot creation and bad-state-root detection), and updates the public and internal snap_sync docs plus the sync_modes doc with the snap/2 wire protocol and BAL replay flow. End-to-end multi-node integration tests are deferred to a future external hive snap/2 simulator.
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Motivation
Implements EIP-8189: snap/2, which replaces iterative trie-node fetching during state healing with Block Access List (EIP-7928) replay. This is cleaner, avoids the need for partial-trie reconstruction, and lets the local node serve the same BALs to peers over snap/2 once sync is complete.
Depends on EIP-7928 (BAL header commitment) already present in this repo.
Description
Wire protocol
snap(2)alongsidesnap(1); per-connection negotiation picks the highest common version.GetBlockAccessLists(0x08) andBlockAccessLists(0x09).GetTrieNodes/TrieNodes; snap/1 connections serve them unchanged.BlockAccessListsresponse:Vec<Option<BlockAccessList>>with 0x80 RLP sentinel for absent entries, preserving position correspondence with the request.rlpx/message.rsguard the new message range againstBASED_CAPABILITY_OFFSET.BAL persistence
BLOCK_ACCESS_LISTSwithstore_block_access_list,get_block_access_list,iter_block_access_lists_by_hashes.execute_blockreturnsOption<BlockAccessList>;store_blocktakesOption<&BlockAccessList>. Pre-Amsterdam blocks passNone.add_block,add_block_pipeline_inner,add_blocks_in_batch.execute_block/execute_block_from_state.Server / client / replay engine
process_block_access_lists_requestrespects a 2 MiB soft cap (BAL_RESPONSE_SOFT_CAP_BYTES); first slot always included; remaining over-cap slots filled withNone.request_block_access_listsreturns(Vec<Option<BlockAccessList>>, peer_id)to keep failure attribution coherent.apply_bal(sync/bal_healing/apply.rs) applies BAL as state diffs: balance/nonce/code/storage post-values; implicit-empty entry triggers account deletion; missing local slots treated as zero pre-value; storage writes go directly to backend.advance_state_via_balsfetches in batches, validates ordering/hash before each apply, applies in strict block order using locally-trackedcurrent_root, persists each BAL. On peer exhaustion falls back to snap/1heal_state_trie_wrap.Sync state machine
Staleness loop in
snap_sync.rsbranches on snap/2 peer reachability: V2 path runsadvance_state_via_balsthen validates finalstate_root; V1 path is unchanged.Tests
process_block_access_lists_request(empty, all-known, mixed, 2 MiB cap, snap/1 rejection).apply_balunit tests: account creation/destruction, storage deletion, code deployment, EIP-7702 delegation clear, fresh storage slot, bad-state-root detection.test/tests/blockchain/batch_tests.rs.cargo test -p ethrex-p2p: 37 passing (was 27).cargo test -p ethrex-test: 421 passing (was 416).Notes
test/tests/p2p/has no multi-node RLPx harness, and the existing hive devp2p snap simulator calls the external Godevp2pCLI. A dedicated hive snap/2 simulator is needed.STORE_SCHEMA_VERSIONincrates/storage/lib.rsfor the newBLOCK_ACCESS_LISTStable.Checklist
STORE_SCHEMA_VERSION(crates/storage/lib.rs) if the PR includes breaking changes to theStorerequiring a re-sync.