From 16d6c78f636dbc5d1bf3a32e0e46e6aa962180f9 Mon Sep 17 00:00:00 2001
From: Csaba Kiraly <csaba.kiraly@gmail.com>
Date: Wed, 16 Apr 2025 09:49:53 +0200
Subject: [PATCH] p2p: add metrics for inbound connection errors

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

# Conflicts:
#	p2p/metrics.go
---
 p2p/metrics.go | 42 ++++++++++++++++++++++++++++++++++++++++++
 p2p/server.go  |  2 ++
 2 files changed, 44 insertions(+)

diff --git a/p2p/metrics.go b/p2p/metrics.go
index 29c2acb0cba3..c44a878aa4ad 100644
--- a/p2p/metrics.go
+++ b/p2p/metrics.go
@@ -66,6 +66,18 @@ var (
 
 	// capture the rest of errors that are not handled by the above meters
 	dialOtherError = metrics.NewRegisteredMeter("p2p/dials/error/other", nil)
+
+	// handshake error meters for inbound connections
+	serveTooManyPeers        = metrics.NewRegisteredMeter("p2p/serves/error/saturated", nil)
+	serveAlreadyConnected    = metrics.NewRegisteredMeter("p2p/serves/error/known", nil)
+	serveSelf                = metrics.NewRegisteredMeter("p2p/serves/error/self", nil)
+	serveUselessPeer         = metrics.NewRegisteredMeter("p2p/serves/error/useless", nil)
+	serveUnexpectedIdentity  = metrics.NewRegisteredMeter("p2p/serves/error/id/unexpected", nil)
+	serveEncHandshakeError   = metrics.NewRegisteredMeter("p2p/serves/error/rlpx/enc", nil) //EOF; connection reset during handshake; (message too big?)
+	serveProtoHandshakeError = metrics.NewRegisteredMeter("p2p/serves/error/rlpx/proto", nil)
+
+	// capture the rest of errors that are not handled by the above meters
+	serveOtherError = metrics.NewRegisteredMeter("p2p/serves/error/other", nil)
 )
 
 // markDialError matches errors that occur while setting up a dial connection to the
@@ -99,6 +111,36 @@ func markDialError(err error) {
 	}
 }
 
+// markServeError matches errors that occur while serving an inbound connection
+// to the corresponding meter.
+func markServeError(err error) {
+	if !metrics.Enabled() {
+		return
+	}
+
+	var reason DiscReason
+	var handshakeErr *protoHandshakeError
+	d := errors.As(err, &reason)
+	switch {
+	case d && reason == DiscTooManyPeers:
+		serveTooManyPeers.Mark(1)
+	case d && reason == DiscAlreadyConnected:
+		serveAlreadyConnected.Mark(1)
+	case d && reason == DiscSelf:
+		serveSelf.Mark(1)
+	case d && reason == DiscUselessPeer:
+		serveUselessPeer.Mark(1)
+	case d && reason == DiscUnexpectedIdentity:
+		serveUnexpectedIdentity.Mark(1)
+	case errors.As(err, &handshakeErr):
+		serveProtoHandshakeError.Mark(1)
+	case errors.Is(err, errEncHandshakeError):
+		serveEncHandshakeError.Mark(1)
+	default:
+		serveOtherError.Mark(1)
+	}
+}
+
 // meteredConn is a wrapper around a net.Conn that meters both the
 // inbound and outbound network traffic.
 type meteredConn struct {
diff --git a/p2p/server.go b/p2p/server.go
index d9105976dd27..f3a58bba2991 100644
--- a/p2p/server.go
+++ b/p2p/server.go
@@ -864,6 +864,8 @@ func (srv *Server) SetupConn(fd net.Conn, flags connFlag, dialDest *enode.Node)
 	if err != nil {
 		if !c.is(inboundConn) {
 			markDialError(err)
+		} else {
+			markServeError(err)
 		}
 		c.close(err)
 	}