Module sync_committee 

Delta encoding for Ethereum sync committees.

Sync committees remain unchanged for an entire sync committee period and are replaced when a new period begins. This makes equality-based encoding sufficient for the normal state-diff window: unchanged committees require no payload, while a committee transition stores the complete target committee.

The module operates on the serialized SSZ representation of a SyncCommittee. It does not inspect individual committee members or SSZ fields; the serialized bytes are treated as an opaque payload.

Encoding strategy

Two representations are possible:

• SyncCommitteeDiff::Unchanged when the serialized base and target committees are identical.
• SyncCommitteeDiff::FullReplacement when the committee has changed.

The replacement representation stores the complete serialized target committee. This is intentional: unlike validator balances or participation flags, there is no useful sparse update representation for a committee in this module.

State transition

Applying a delta to the same base committee used during diff generation reconstructs the target bytes:

base committee + delta -> target committee

The delta does not depend on the committee period number. The caller is responsible for determining which consensus-state field is being diffed.

SSZ representation

The functions accept the raw serialized bytes of the SyncCommittee container. The bytes are treated as opaque data and are copied without decoding or re-encoding individual committee members.

SyncCommittee is a fixed-size consensus container. Callers should therefore normally provide the serialized container bytes directly rather than adding a list-length prefix.

Complexity

Let n be the serialized size of the committee:

• diff_sync_committee performs an O(n) byte comparison.
• apply_sync_committee is O(1) for SyncCommitteeDiff::Unchanged.
• apply_sync_committee is O(n) for SyncCommitteeDiff::FullReplacement.

Additional memory is O(n) when a changed committee is encoded, because the target bytes are copied into the replacement payload.

Example

use eth_state_diff::sync_committee::diff_sync_committee;
use eth_state_diff::types::SyncCommitteeDiff;

let base = b"committee-a";
let target = b"committee-a";

let delta = diff_sync_committee(base, target);

assert_eq!(delta, SyncCommitteeDiff::Unchanged);

A committee transition produces a full replacement:

use eth_state_diff::sync_committee::diff_sync_committee;
use eth_state_diff::types::SyncCommitteeDiff;

let base = b"committee-a";
let target = b"committee-b";

let delta = diff_sync_committee(base, target);

assert_eq!(
    delta,
    SyncCommitteeDiff::FullReplacement(target.to_vec())
);

Functions

apply_sync_committee

Applies a sync committee delta to a serialized SSZ committee in place.

diff_sync_committee

Computes a delta between two serialized Ethereum sync committees.