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/enrcmd.go

@@ -0,0 +1,198 @@
+// 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/base64"
+	"encoding/hex"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"os"
+	"strconv"
+	"strings"
+
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/p2p/enr"
+	"github.com/ethereum/go-ethereum/rlp"
+	"gopkg.in/urfave/cli.v1"
+)
+
+var enrdumpCommand = cli.Command{
+	Name:   "enrdump",
+	Usage:  "Pretty-prints node records",
+	Action: enrdump,
+	Flags: []cli.Flag{
+		cli.StringFlag{Name: "file"},
+	},
+}
+
+func enrdump(ctx *cli.Context) error {
+	var source string
+	if file := ctx.String("file"); file != "" {
+		if ctx.NArg() != 0 {
+			return fmt.Errorf("can't dump record from command-line argument in -file mode")
+		}
+		var b []byte
+		var err error
+		if file == "-" {
+			b, err = ioutil.ReadAll(os.Stdin)
+		} else {
+			b, err = ioutil.ReadFile(file)
+		}
+		if err != nil {
+			return err
+		}
+		source = string(b)
+	} else if ctx.NArg() == 1 {
+		source = ctx.Args()[0]
+	} else {
+		return fmt.Errorf("need record as argument")
+	}
+
+	r, err := parseRecord(source)
+	if err != nil {
+		return fmt.Errorf("INVALID: %v", err)
+	}
+	fmt.Print(dumpRecord(r))
+	return nil
+}
+
+// dumpRecord creates a human-readable description of the given node record.
+func dumpRecord(r *enr.Record) string {
+	out := new(bytes.Buffer)
+	if n, err := enode.New(enode.ValidSchemes, r); err != nil {
+		fmt.Fprintf(out, "INVALID: %v\n", err)
+	} else {
+		fmt.Fprintf(out, "Node ID: %v\n", n.ID())
+	}
+	kv := r.AppendElements(nil)[1:]
+	fmt.Fprintf(out, "Record has sequence number %d and %d key/value pairs.\n", r.Seq(), len(kv)/2)
+	fmt.Fprint(out, dumpRecordKV(kv, 2))
+	return out.String()
+}
+
+func dumpRecordKV(kv []interface{}, indent int) string {
+	// Determine the longest key name for alignment.
+	var out string
+	var longestKey = 0
+	for i := 0; i < len(kv); i += 2 {
+		key := kv[i].(string)
+		if len(key) > longestKey {
+			longestKey = len(key)
+		}
+	}
+	// Print the keys, invoking formatters for known keys.
+	for i := 0; i < len(kv); i += 2 {
+		key := kv[i].(string)
+		val := kv[i+1].(rlp.RawValue)
+		pad := longestKey - len(key)
+		out += strings.Repeat(" ", indent) + strconv.Quote(key) + strings.Repeat(" ", pad+1)
+		formatter := attrFormatters[key]
+		if formatter == nil {
+			formatter = formatAttrRaw
+		}
+		fmtval, ok := formatter(val)
+		if ok {
+			out += fmtval + "\n"
+		} else {
+			out += hex.EncodeToString(val) + " (!)\n"
+		}
+	}
+	return out
+}
+
+// parseNode parses a node record and verifies its signature.
+func parseNode(source string) (*enode.Node, error) {
+	if strings.HasPrefix(source, "enode://") {
+		return enode.ParseV4(source)
+	}
+	r, err := parseRecord(source)
+	if err != nil {
+		return nil, err
+	}
+	return enode.New(enode.ValidSchemes, r)
+}
+
+// parseRecord parses a node record from hex, base64, or raw binary input.
+func parseRecord(source string) (*enr.Record, error) {
+	bin := []byte(source)
+	if d, ok := decodeRecordHex(bytes.TrimSpace(bin)); ok {
+		bin = d
+	} else if d, ok := decodeRecordBase64(bytes.TrimSpace(bin)); ok {
+		bin = d
+	}
+	var r enr.Record
+	err := rlp.DecodeBytes(bin, &r)
+	return &r, err
+}
+
+func decodeRecordHex(b []byte) ([]byte, bool) {
+	if bytes.HasPrefix(b, []byte("0x")) {
+		b = b[2:]
+	}
+	dec := make([]byte, hex.DecodedLen(len(b)))
+	_, err := hex.Decode(dec, b)
+	return dec, err == nil
+}
+
+func decodeRecordBase64(b []byte) ([]byte, bool) {
+	if bytes.HasPrefix(b, []byte("enr:")) {
+		b = b[4:]
+	}
+	dec := make([]byte, base64.RawURLEncoding.DecodedLen(len(b)))
+	n, err := base64.RawURLEncoding.Decode(dec, b)
+	return dec[:n], err == nil
+}
+
+// attrFormatters contains formatting functions for well-known ENR keys.
+var attrFormatters = map[string]func(rlp.RawValue) (string, bool){
+	"id":   formatAttrString,
+	"ip":   formatAttrIP,
+	"ip6":  formatAttrIP,
+	"tcp":  formatAttrUint,
+	"tcp6": formatAttrUint,
+	"udp":  formatAttrUint,
+	"udp6": formatAttrUint,
+}
+
+func formatAttrRaw(v rlp.RawValue) (string, bool) {
+	s := hex.EncodeToString(v)
+	return s, true
+}
+
+func formatAttrString(v rlp.RawValue) (string, bool) {
+	content, _, err := rlp.SplitString(v)
+	return strconv.Quote(string(content)), err == nil
+}
+
+func formatAttrIP(v rlp.RawValue) (string, bool) {
+	content, _, err := rlp.SplitString(v)
+	if err != nil || len(content) != 4 && len(content) != 6 {
+		return "", false
+	}
+	return net.IP(content).String(), true
+}
+
+func formatAttrUint(v rlp.RawValue) (string, bool) {
+	var x uint64
+	if err := rlp.DecodeBytes(v, &x); err != nil {
+		return "", false
+	}
+	return strconv.FormatUint(x, 10), true
+}