p2p/discover: add initial discovery v5 implementation (#20750)

This adds an implementation of the current discovery v5 spec.

There is full integration with cmd/devp2p and enode.Iterator in this
version. In theory we could enable the new protocol as a replacement of
discovery v4 at any time. In practice, there will likely be a few more
changes to the spec and implementation before this can happen.

p2p/enode/nodedb.go

@@ -41,6 +41,7 @@ const (
 	dbNodePrefix   = "n:"      // Identifier to prefix node entries with
 	dbLocalPrefix  = "local:"
 	dbDiscoverRoot = "v4"
+	dbDiscv5Root   = "v5"
 
 	// These fields are stored per ID and IP, the full key is "n:<ID>:v4:<IP>:findfail".
 	// Use nodeItemKey to create those keys.
@@ -172,6 +173,16 @@ func splitNodeItemKey(key []byte) (id ID, ip net.IP, field string) {
 	return id, ip, field
 }
 
+func v5Key(id ID, ip net.IP, field string) []byte {
+	return bytes.Join([][]byte{
+		[]byte(dbNodePrefix),
+		id[:],
+		[]byte(dbDiscv5Root),
+		ip.To16(),
+		[]byte(field),
+	}, []byte{':'})
+}
+
 // localItemKey returns the key of a local node item.
 func localItemKey(id ID, field string) []byte {
 	key := append([]byte(dbLocalPrefix), id[:]...)
@@ -378,6 +389,16 @@ func (db *DB) UpdateFindFails(id ID, ip net.IP, fails int) error {
 	return db.storeInt64(nodeItemKey(id, ip, dbNodeFindFails), int64(fails))
 }
 
+// FindFailsV5 retrieves the discv5 findnode failure counter.
+func (db *DB) FindFailsV5(id ID, ip net.IP) int {
+	return int(db.fetchInt64(v5Key(id, ip, dbNodeFindFails)))
+}
+
+// UpdateFindFailsV5 stores the discv5 findnode failure counter.
+func (db *DB) UpdateFindFailsV5(id ID, ip net.IP, fails int) error {
+	return db.storeInt64(v5Key(id, ip, dbNodeFindFails), int64(fails))
+}
+
 // LocalSeq retrieves the local record sequence counter.
 func (db *DB) localSeq(id ID) uint64 {
 	return db.fetchUint64(localItemKey(id, dbLocalSeq))