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

3 files changed, 14 insertions, 8 deletions

diff --git a/p2p/discover/table.go b/p2p/discover/table.go
index 3460e8377..e0a46792b 100644
--- a/p2p/discover/table.go
+++ b/p2p/discover/table.go
@@ -85,10 +85,10 @@ type Table struct {
 // transport is implemented by the UDP transports.
 type transport interface {
 	Self() *enode.Node
+	RequestENR(*enode.Node) (*enode.Node, error)
 	lookupRandom() []*enode.Node
 	lookupSelf() []*enode.Node
 	ping(*enode.Node) (seq uint64, err error)
-	requestENR(*enode.Node) (*enode.Node, error)
 }
 
 // bucket contains nodes, ordered by their last activity. the entry
@@ -344,7 +344,7 @@ func (tab *Table) doRevalidate(done chan<- struct{}) {
 
 	// Also fetch record if the node replied and returned a higher sequence number.
 	if last.Seq() < remoteSeq {
-		n, err := tab.net.requestENR(unwrapNode(last))
+		n, err := tab.net.RequestENR(unwrapNode(last))
 		if err != nil {
 			tab.log.Debug("ENR request failed", "id", last.ID(), "addr", last.addr(), "err", err)
 		} else {
diff --git a/p2p/discover/table_util_test.go b/p2p/discover/table_util_test.go
index 3075c4340..8e5fc7374 100644
--- a/p2p/discover/table_util_test.go
+++ b/p2p/discover/table_util_test.go
@@ -145,7 +145,7 @@ func (t *pingRecorder) ping(n *enode.Node) (seq uint64, err error) {
 }
 
 // requestENR simulates an ENR request.
-func (t *pingRecorder) requestENR(n *enode.Node) (*enode.Node, error) {
+func (t *pingRecorder) RequestENR(n *enode.Node) (*enode.Node, error) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 
diff --git a/p2p/discover/v4_udp.go b/p2p/discover/v4_udp.go
index b3569b671..b2a5d85cf 100644
--- a/p2p/discover/v4_udp.go
+++ b/p2p/discover/v4_udp.go
@@ -415,13 +415,13 @@ func (t *UDPv4) lookupWorker(n *node, targetKey encPubkey, reply chan<- []*node)
 // version of the node record for it. It returns n if the node could not be resolved.
 func (t *UDPv4) Resolve(n *enode.Node) *enode.Node {
 	// Try asking directly. This works if the node is still responding on the endpoint we have.
-	if rn, err := t.requestENR(n); err == nil {
+	if rn, err := t.RequestENR(n); err == nil {
 		return rn
 	}
 	// Check table for the ID, we might have a newer version there.
 	if intable := t.tab.getNode(n.ID()); intable != nil && intable.Seq() > n.Seq() {
 		n = intable
-		if rn, err := t.requestENR(n); err == nil {
+		if rn, err := t.RequestENR(n); err == nil {
 			return rn
 		}
 	}
@@ -433,7 +433,7 @@ func (t *UDPv4) Resolve(n *enode.Node) *enode.Node {
 	result := t.LookupPubkey((*ecdsa.PublicKey)(&key))
 	for _, rn := range result {
 		if rn.ID() == n.ID() {
-			if rn, err := t.requestENR(rn); err == nil {
+			if rn, err := t.RequestENR(rn); err == nil {
 				return rn
 			}
 		}
@@ -447,6 +447,12 @@ func (t *UDPv4) ourEndpoint() rpcEndpoint {
 	return makeEndpoint(a, uint16(n.TCP()))
 }
 
+// Ping sends a ping message to the given node.
+func (t *UDPv4) Ping(n *enode.Node) error {
+	_, err := t.ping(n)
+	return err
+}
+
 // ping sends a ping message to the given node and waits for a reply.
 func (t *UDPv4) ping(n *enode.Node) (seq uint64, err error) {
 	rm := t.sendPing(n.ID(), &net.UDPAddr{IP: n.IP(), Port: n.UDP()}, nil)
@@ -521,8 +527,8 @@ func (t *UDPv4) findnode(toid enode.ID, toaddr *net.UDPAddr, target encPubkey) (
 	return nodes, <-rm.errc
 }
 
-// requestENR sends enrRequest to the given node and waits for a response.
-func (t *UDPv4) requestENR(n *enode.Node) (*enode.Node, error) {
+// RequestENR sends enrRequest to the given node and waits for a response.
+func (t *UDPv4) RequestENR(n *enode.Node) (*enode.Node, error) {
 	addr := &net.UDPAddr{IP: n.IP(), Port: n.UDP()}
 	t.ensureBond(n.ID(), addr)