cmd/devp2p: add discv4 RPC server

cmd/devp2p/discv4cmd.go

@@ -20,6 +20,8 @@ import (
 	"errors"
 	"fmt"
 	"net"
+	"net/http"
+	"net/rpc"
 	"strconv"
 	"strings"
 	"time"
@@ -28,6 +30,7 @@ import (
 	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/internal/flags"
+	"github.com/ethereum/go-ethereum/log"
 	"github.com/ethereum/go-ethereum/p2p/discover"
 	"github.com/ethereum/go-ethereum/p2p/enode"
 	"github.com/ethereum/go-ethereum/params"
@@ -131,6 +134,10 @@ var (
 		Usage:   "Enode of the remote node under test",
 		EnvVars: []string{"REMOTE_ENODE"},
 	}
+	httpAddrFlag = &cli.StringFlag{
+		Name:  "rpc",
+		Usage: "HTTP server listening address",
+	}
 )
 
 var discoveryNodeFlags = []cli.Flag{
@@ -154,6 +161,27 @@ func discv4Ping(ctx *cli.Context) error {
 	return nil
 }
 
+func discv4Listen(ctx *cli.Context) error {
+	disc, _ := startV4(ctx)
+	defer disc.Close()
+
+	fmt.Println(disc.Self())
+
+	httpAddr := ctx.String(httpAddrFlag.Name)
+	if httpAddr == "" {
+		// Non-HTTP mode.
+		select {}
+	}
+
+	api := &discv4API{disc}
+	log.Info("Starting RPC API server", "addr", httpAddr)
+	srv := rpc.NewServer()
+	srv.RegisterName("discv4", api)
+	http.DefaultServeMux.Handle("/", srv)
+	httpsrv := http.Server{Addr: httpAddr, Handler: http.DefaultServeMux}
+	return httpsrv.ListenAndServe()
+}
+
 func discv4RequestRecord(ctx *cli.Context) error {
 	n := getNodeArg(ctx)
 	disc, _ := startV4(ctx)
@@ -362,3 +390,23 @@ func parseBootnodes(ctx *cli.Context) ([]*enode.Node, error) {
 	}
 	return nodes, nil
 }
+
+type discv4API struct {
+	host *discover.UDPv4
+}
+
+func (api *discv4API) LookupRandom(n int) (ns []*enode.Node) {
+	it := api.host.RandomNodes()
+	for len(ns) < n && it.Next() {
+		ns = append(ns, it.Node())
+	}
+	return ns
+}
+
+func (api *discv4API) Buckets() [][]discover.BucketNode {
+	return api.host.TableBuckets()
+}
+
+func (api *discv4API) Self() *enode.Node {
+	return api.host.Self()
+}