les: historical data garbage collection (#19570)

This change introduces garbage collection for the light client. Historical
chain data is deleted periodically. If you want to disable the GC, use
the --light.nopruning flag.

core/rawdb/accessors_indexes.go

@@ -17,6 +17,7 @@
 package rawdb
 
 import (
+	"bytes"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -151,3 +152,24 @@ func WriteBloomBits(db ethdb.KeyValueWriter, bit uint, section uint64, head comm
 		log.Crit("Failed to store bloom bits", "err", err)
 	}
 }
+
+// DeleteBloombits removes all compressed bloom bits vector belonging to the
+// given section range and bit index.
+func DeleteBloombits(db ethdb.Database, bit uint, from uint64, to uint64) {
+	start, end := bloomBitsKey(bit, from, common.Hash{}), bloomBitsKey(bit, to, common.Hash{})
+	it := db.NewIterator(nil, start)
+	defer it.Release()
+
+	for it.Next() {
+		if bytes.Compare(it.Key(), end) >= 0 {
+			break
+		}
+		if len(it.Key()) != len(bloomBitsPrefix)+2+8+32 {
+			continue
+		}
+		db.Delete(it.Key())
+	}
+	if it.Error() != nil {
+		log.Crit("Failed to delete bloom bits", "err", it.Error())
+	}
+}