p2p/dnsdisc: add implementation of EIP-1459 (#20094)

This adds an implementation of node discovery via DNS TXT records to the
go-ethereum library. The implementation doesn't match EIP-1459 exactly,
the main difference being that this implementation uses separate merkle
trees for tree links and ENRs. The EIP will be updated to match p2p/dnsdisc.

To maintain DNS trees, cmd/devp2p provides a frontend for the p2p/dnsdisc
library. The new 'dns' subcommands can be used to create, sign and deploy DNS
discovery trees.

cmd/devp2p/nodeset.go

@@ -0,0 +1,87 @@
+// Copyright 2019 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum 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 General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"sort"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+const jsonIndent = "    "
+
+// nodeSet is the nodes.json file format. It holds a set of node records
+// as a JSON object.
+type nodeSet map[enode.ID]nodeJSON
+
+type nodeJSON struct {
+	Seq uint64      `json:"seq"`
+	N   *enode.Node `json:"record"`
+}
+
+func loadNodesJSON(file string) nodeSet {
+	var nodes nodeSet
+	if err := common.LoadJSON(file, &nodes); err != nil {
+		exit(err)
+	}
+	return nodes
+}
+
+func writeNodesJSON(file string, nodes nodeSet) {
+	nodesJSON, err := json.MarshalIndent(nodes, "", jsonIndent)
+	if err != nil {
+		exit(err)
+	}
+	if err := ioutil.WriteFile(file, nodesJSON, 0644); err != nil {
+		exit(err)
+	}
+}
+
+func (ns nodeSet) nodes() []*enode.Node {
+	result := make([]*enode.Node, 0, len(ns))
+	for _, n := range ns {
+		result = append(result, n.N)
+	}
+	// Sort by ID.
+	sort.Slice(result, func(i, j int) bool {
+		return bytes.Compare(result[i].ID().Bytes(), result[j].ID().Bytes()) < 0
+	})
+	return result
+}
+
+func (ns nodeSet) add(nodes ...*enode.Node) {
+	for _, n := range nodes {
+		ns[n.ID()] = nodeJSON{Seq: n.Seq(), N: n}
+	}
+}
+
+func (ns nodeSet) verify() error {
+	for id, n := range ns {
+		if n.N.ID() != id {
+			return fmt.Errorf("invalid node %v: ID does not match ID %v in record", id, n.N.ID())
+		}
+		if n.N.Seq() != n.Seq {
+			return fmt.Errorf("invalid node %v: 'seq' does not match seq %d from record", id, n.N.Seq())
+		}
+	}
+	return nil
+}