cmd/devp2p: add combined discovery listener

Add `devp2p discovery listen`, which runs all supported discovery
protocol versions (discv4 and discv5) on a single UDP socket, the way a
real node does. For a single-protocol node, `discv4 listen` /
`discv5 listen` remain.

Also expose the --rpc debug API on `discv5 listen`, for parity with
`discv4 listen`.

cmd/devp2p/README.md

@@ -80,6 +80,13 @@ Run `devp2p discv5 listen` to run a Discovery v5 node.
 Run `devp2p discv5 crawl <nodes.json path>` to create or update a JSON node set containing
 discv5 nodes.
 
+### Combined Discovery
+
+Run `devp2p discovery listen` to run a node speaking all supported discovery protocol
+versions (currently discv4 and discv5) on a single UDP port. For a single-protocol node, use
+`devp2p discv4 listen` or `devp2p discv5 listen`. Add `--rpc <addr>` to expose the
+per-protocol HTTP API (`discv4_*`, `discv5_*`).
+
 ### Discovery Test Suites
 
 The devp2p command also contains interactive test suites for Discovery v4 and Discovery

cmd/devp2p/discoverycmd.go

@@ -0,0 +1,112 @@
+// Copyright 2026 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 (
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"net/netip"
+	"slices"
+
+	"github.com/ethereum/go-ethereum/log"
+	"github.com/ethereum/go-ethereum/p2p/discover"
+	"github.com/ethereum/go-ethereum/rpc"
+	"github.com/urfave/cli/v2"
+)
+
+var (
+	discoveryCommand = &cli.Command{
+		Name:  "discovery",
+		Usage: "Node Discovery tools",
+		Subcommands: []*cli.Command{
+			discoveryListenCommand,
+		},
+	}
+	discoveryListenCommand = &cli.Command{
+		Name:   "listen",
+		Usage:  "Runs a discovery node speaking all supported protocol versions on one UDP port",
+		Action: discoveryListen,
+		Flags: slices.Concat(discoveryNodeFlags, []cli.Flag{
+			httpAddrFlag,
+		}),
+	}
+)
+
+func discoveryListen(ctx *cli.Context) error {
+	ln, config := makeDiscoveryConfig(ctx)
+	socket := listen(ctx, ln)
+
+	// v4 is the primary listener on the real socket and forwards packets it
+	// can't parse to v5 via the unhandled channel.
+	unhandled := make(chan discover.ReadPacket, 100)
+	config.Unhandled = unhandled
+	v4, err := discover.ListenV4(socket, ln, config)
+	if err != nil {
+		exit(err)
+	}
+	config.Unhandled = nil
+	v5, err := discover.ListenV5(&sharedUDPConn{socket, unhandled}, ln, config)
+	if err != nil {
+		exit(err)
+	}
+	// Close v4 before v5: when sharing the socket, v5's read loop only unblocks
+	// once v4 closes the underlying socket and the unhandled channel.
+	defer func() {
+		v4.Close()
+		v5.Close()
+	}()
+
+	// v4 and v5 share the same local node, so this is the single record both announce.
+	fmt.Println(ln.Node())
+
+	httpAddr := ctx.String(httpAddrFlag.Name)
+	if httpAddr == "" {
+		select {}
+	}
+
+	srv := rpc.NewServer()
+	srv.RegisterName("discv4", &discv4API{v4})
+	srv.RegisterName("discv5", &discv5API{v5})
+	log.Info("Starting RPC API server", "addr", httpAddr)
+	http.DefaultServeMux.Handle("/", srv)
+	httpsrv := http.Server{Addr: httpAddr, Handler: http.DefaultServeMux}
+	return httpsrv.ListenAndServe()
+}
+
+// sharedUDPConn implements a shared connection, identical to the one used by
+// p2p.Server: reads return packets the primary v4 listener found unprocessable
+// and forwarded on the unhandled channel.
+type sharedUDPConn struct {
+	*net.UDPConn
+	unhandled chan discover.ReadPacket
+}
+
+func (s *sharedUDPConn) ReadFromUDPAddrPort(b []byte) (n int, addr netip.AddrPort, err error) {
+	packet, ok := <-s.unhandled
+	if !ok {
+		return 0, netip.AddrPort{}, errors.New("connection was closed")
+	}
+	l := min(len(packet.Data), len(b))
+	copy(b[:l], packet.Data[:l])
+	return l, packet.Addr, nil
+}
+
+func (s *sharedUDPConn) Close() error {
+	return nil
+}

cmd/devp2p/discv5cmd.go

@@ -19,12 +19,16 @@ package main
 import (
 	"errors"
 	"fmt"
+	"net/http"
 	"slices"
 	"time"
 
 	"github.com/ethereum/go-ethereum/cmd/devp2p/internal/v5test"
 	"github.com/ethereum/go-ethereum/common"
+	"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/rpc"
 	"github.com/urfave/cli/v2"
 )
 
@@ -76,7 +80,9 @@ var (
 		Name:   "listen",
 		Usage:  "Runs a node",
 		Action: discv5Listen,
-		Flags:  discoveryNodeFlags,
+		Flags: slices.Concat(discoveryNodeFlags, []cli.Flag{
+			httpAddrFlag,
+		}),
 	}
 )
 
@@ -137,7 +143,20 @@ func discv5Listen(ctx *cli.Context) error {
 	defer disc.Close()
 
 	fmt.Println(disc.Self())
-	select {}
+
+	httpAddr := ctx.String(httpAddrFlag.Name)
+	if httpAddr == "" {
+		// Non-HTTP mode.
+		select {}
+	}
+
+	api := &discv5API{disc}
+	log.Info("Starting RPC API server", "addr", httpAddr)
+	srv := rpc.NewServer()
+	srv.RegisterName("discv5", api)
+	http.DefaultServeMux.Handle("/", srv)
+	httpsrv := http.Server{Addr: httpAddr, Handler: http.DefaultServeMux}
+	return httpsrv.ListenAndServe()
 }
 
 // startV5 starts an ephemeral discovery v5 node.
@@ -150,3 +169,19 @@ func startV5(ctx *cli.Context) (*discover.UDPv5, discover.Config) {
 	}
 	return disc, config
 }
+
+type discv5API struct {
+	host *discover.UDPv5
+}
+
+func (api *discv5API) 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 *discv5API) Self() *enode.Node {
+	return api.host.Self()
+}

cmd/devp2p/main.go

@@ -49,6 +49,7 @@ func init() {
 		keyCommand,
 		discv4Command,
 		discv5Command,
+		discoveryCommand,
 		dnsCommand,
 		nodesetCommand,
 		rlpxCommand,