beacon/light: add CommitteeChain (#27766)

This change implements CommitteeChain which is a key component of the beacon light client. It is a passive data structure that can validate, hold and update a chain of beacon light sync committees and updates, starting from a checkpoint that proves the starting committee through a beacon block hash, header and corresponding state. Once synced to the current sync period, CommitteeChain can also validate signed beacon headers.

beacon/light/canonical.go

@@ -0,0 +1,125 @@
+// Copyright 2023 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package light
+
+import (
+	"encoding/binary"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/common/lru"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+// canonicalStore stores instances of the given type in a database and caches
+// them in memory, associated with a continuous range of period numbers.
+// Note: canonicalStore is not thread safe and it is the caller's responsibility
+// to avoid concurrent access.
+type canonicalStore[T any] struct {
+	keyPrefix []byte
+	periods   periodRange
+	cache     *lru.Cache[uint64, T]
+}
+
+// newCanonicalStore creates a new canonicalStore and loads all keys associated
+// with the keyPrefix in order to determine the ranges available in the database.
+func newCanonicalStore[T any](db ethdb.Iteratee, keyPrefix []byte) (*canonicalStore[T], error) {
+	cs := &canonicalStore[T]{
+		keyPrefix: keyPrefix,
+		cache:     lru.NewCache[uint64, T](100),
+	}
+	var (
+		iter  = db.NewIterator(keyPrefix, nil)
+		kl    = len(keyPrefix)
+		first = true
+	)
+	defer iter.Release()
+
+	for iter.Next() {
+		if len(iter.Key()) != kl+8 {
+			log.Warn("Invalid key length in the canonical chain database", "key", fmt.Sprintf("%#x", iter.Key()))
+			continue
+		}
+		period := binary.BigEndian.Uint64(iter.Key()[kl : kl+8])
+		if first {
+			cs.periods.Start = period
+		} else if cs.periods.End != period {
+			return nil, fmt.Errorf("gap in the canonical chain database between periods %d and %d", cs.periods.End, period-1)
+		}
+		first = false
+		cs.periods.End = period + 1
+	}
+	return cs, nil
+}
+
+// databaseKey returns the database key belonging to the given period.
+func (cs *canonicalStore[T]) databaseKey(period uint64) []byte {
+	return binary.BigEndian.AppendUint64(append([]byte{}, cs.keyPrefix...), period)
+}
+
+// add adds the given item to the database. It also ensures that the range remains
+// continuous. Can be used either with a batch or database backend.
+func (cs *canonicalStore[T]) add(backend ethdb.KeyValueWriter, period uint64, value T) error {
+	if !cs.periods.canExpand(period) {
+		return fmt.Errorf("period expansion is not allowed, first: %d, next: %d, period: %d", cs.periods.Start, cs.periods.End, period)
+	}
+	enc, err := rlp.EncodeToBytes(value)
+	if err != nil {
+		return err
+	}
+	if err := backend.Put(cs.databaseKey(period), enc); err != nil {
+		return err
+	}
+	cs.cache.Add(period, value)
+	cs.periods.expand(period)
+	return nil
+}
+
+// deleteFrom removes items starting from the given period.
+func (cs *canonicalStore[T]) deleteFrom(db ethdb.KeyValueWriter, fromPeriod uint64) (deleted periodRange) {
+	keepRange, deleteRange := cs.periods.split(fromPeriod)
+	deleteRange.each(func(period uint64) {
+		db.Delete(cs.databaseKey(period))
+		cs.cache.Remove(period)
+	})
+	cs.periods = keepRange
+	return deleteRange
+}
+
+// get returns the item at the given period or the null value of the given type
+// if no item is present.
+func (cs *canonicalStore[T]) get(backend ethdb.KeyValueReader, period uint64) (T, bool) {
+	var null, value T
+	if !cs.periods.contains(period) {
+		return null, false
+	}
+	if value, ok := cs.cache.Get(period); ok {
+		return value, true
+	}
+	enc, err := backend.Get(cs.databaseKey(period))
+	if err != nil {
+		log.Error("Canonical store value not found", "period", period, "start", cs.periods.Start, "end", cs.periods.End)
+		return null, false
+	}
+	if err := rlp.DecodeBytes(enc, &value); err != nil {
+		log.Error("Error decoding canonical store value", "error", err)
+		return null, false
+	}
+	cs.cache.Add(period, value)
+	return value, true
+}