les: add empty "les" ENR entry for servers (ethereum#20145)

les/enr_entry.go

@@ -0,0 +1,32 @@
+// Copyright 2019 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 les
+
+import (
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+// lesEntry is the "les" ENR entry. This is set for LES servers only.
+type lesEntry struct {
+	// Ignore additional fields (for forward compatibility).
+	Rest []rlp.RawValue `rlp:"tail"`
+}
+
+// ENRKey implements enr.Entry.
+func (e lesEntry) ENRKey() string {
+	return "les"
+}

les/server.go

@@ -30,6 +30,7 @@ import (
 	"github.com/ethereum/go-ethereum/p2p"
 	"github.com/ethereum/go-ethereum/p2p/discv5"
 	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/p2p/enr"
 	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/rpc"
 )
@@ -136,12 +137,17 @@ func (s *LesServer) APIs() []rpc.API {
 }
 
 func (s *LesServer) Protocols() []p2p.Protocol {
-	return s.makeProtocols(ServerProtocolVersions, s.handler.runPeer, func(id enode.ID) interface{} {
+	ps := s.makeProtocols(ServerProtocolVersions, s.handler.runPeer, func(id enode.ID) interface{} {
 		if p := s.peers.Peer(peerIdToString(id)); p != nil {
 			return p.Info()
 		}
 		return nil
 	})
+	// Add "les" ENR entries.
+	for i := range ps {
+		ps[i].Attributes = []enr.Entry{&lesEntry{}}
+	}
+	return ps
 }
 
 // Start starts the LES server