cmd/devp2p: add devp2p debug tool (#19657)

* p2p/discover: export Ping and RequestENR

These two are useful for checking the status of a node.

* cmd/devp2p: add devp2p debug tool

This is a new tool for debugging p2p issues. It supports a few
basic tasks for now, but many more things can and will be added
in the near future.

   devp2p enrdump            -- prints ENRs readably
   devp2p discv4 ping        -- checks if a node is up
   devp2p discv4 requestenr  -- gets a node's record
   devp2p discv4 resolve     -- finds a node through the DHT

cmd/devp2p/discv4cmd.go

@@ -0,0 +1,166 @@
+// 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 (
+	"fmt"
+	"net"
+	"sort"
+	"strings"
+	"time"
+
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/p2p/discover"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/params"
+	"gopkg.in/urfave/cli.v1"
+)
+
+var (
+	discv4Command = cli.Command{
+		Name:  "discv4",
+		Usage: "Node Discovery v4 tools",
+		Subcommands: []cli.Command{
+			discv4PingCommand,
+			discv4RequestRecordCommand,
+			discv4ResolveCommand,
+		},
+	}
+	discv4PingCommand = cli.Command{
+		Name:   "ping",
+		Usage:  "Sends ping to a node",
+		Action: discv4Ping,
+	}
+	discv4RequestRecordCommand = cli.Command{
+		Name:   "requestenr",
+		Usage:  "Requests a node record using EIP-868 enrRequest",
+		Action: discv4RequestRecord,
+	}
+	discv4ResolveCommand = cli.Command{
+		Name:   "resolve",
+		Usage:  "Finds a node in the DHT",
+		Action: discv4Resolve,
+		Flags:  []cli.Flag{bootnodesFlag},
+	}
+)
+
+var bootnodesFlag = cli.StringFlag{
+	Name:  "bootnodes",
+	Usage: "Comma separated nodes used for bootstrapping",
+}
+
+func discv4Ping(ctx *cli.Context) error {
+	n, disc, err := getNodeArgAndStartV4(ctx)
+	if err != nil {
+		return err
+	}
+	defer disc.Close()
+
+	start := time.Now()
+	if err := disc.Ping(n); err != nil {
+		return fmt.Errorf("node didn't respond: %v", err)
+	}
+	fmt.Printf("node responded to ping (RTT %v).\n", time.Since(start))
+	return nil
+}
+
+func discv4RequestRecord(ctx *cli.Context) error {
+	n, disc, err := getNodeArgAndStartV4(ctx)
+	if err != nil {
+		return err
+	}
+	defer disc.Close()
+
+	respN, err := disc.RequestENR(n)
+	if err != nil {
+		return fmt.Errorf("can't retrieve record: %v", err)
+	}
+	fmt.Println(respN.String())
+	return nil
+}
+
+func discv4Resolve(ctx *cli.Context) error {
+	n, disc, err := getNodeArgAndStartV4(ctx)
+	if err != nil {
+		return err
+	}
+	defer disc.Close()
+
+	fmt.Println(disc.Resolve(n).String())
+	return nil
+}
+
+func getNodeArgAndStartV4(ctx *cli.Context) (*enode.Node, *discover.UDPv4, error) {
+	if ctx.NArg() != 1 {
+		return nil, nil, fmt.Errorf("missing node as command-line argument")
+	}
+	n, err := parseNode(ctx.Args()[0])
+	if err != nil {
+		return nil, nil, err
+	}
+	var bootnodes []*enode.Node
+	if commandHasFlag(ctx, bootnodesFlag) {
+		bootnodes, err = parseBootnodes(ctx)
+		if err != nil {
+			return nil, nil, err
+		}
+	}
+	disc, err := startV4(bootnodes)
+	return n, disc, err
+}
+
+func parseBootnodes(ctx *cli.Context) ([]*enode.Node, error) {
+	s := params.RinkebyBootnodes
+	if ctx.IsSet(bootnodesFlag.Name) {
+		s = strings.Split(ctx.String(bootnodesFlag.Name), ",")
+	}
+	nodes := make([]*enode.Node, len(s))
+	var err error
+	for i, record := range s {
+		nodes[i], err = parseNode(record)
+		if err != nil {
+			return nil, fmt.Errorf("invalid bootstrap node: %v", err)
+		}
+	}
+	return nodes, nil
+}
+
+// commandHasFlag returns true if the current command supports the given flag.
+func commandHasFlag(ctx *cli.Context, flag cli.Flag) bool {
+	flags := ctx.FlagNames()
+	sort.Strings(flags)
+	i := sort.SearchStrings(flags, flag.GetName())
+	return i != len(flags) && flags[i] == flag.GetName()
+}
+
+// startV4 starts an ephemeral discovery V4 node.
+func startV4(bootnodes []*enode.Node) (*discover.UDPv4, error) {
+	var cfg discover.Config
+	cfg.Bootnodes = bootnodes
+	cfg.PrivateKey, _ = crypto.GenerateKey()
+	db, _ := enode.OpenDB("")
+	ln := enode.NewLocalNode(db, cfg.PrivateKey)
+
+	socket, err := net.ListenUDP("udp4", &net.UDPAddr{IP: net.IP{0, 0, 0, 0}})
+	if err != nil {
+		return nil, err
+	}
+	addr := socket.LocalAddr().(*net.UDPAddr)
+	ln.SetFallbackIP(net.IP{127, 0, 0, 1})
+	ln.SetFallbackUDP(addr.Port)
+	return discover.ListenUDP(socket, ln, cfg)
+}