From 4e6dd45415efbf4657f690dcd5a7f9524a25604c Mon Sep 17 00:00:00 2001
From: Graham McIntire <graham@mcintire.me>
Date: Thu, 12 Feb 2026 10:02:54 -0600
Subject: [PATCH] use raw ICMP ping with exec fallback for unprivileged
 environments

---
 go.mod       |   1 +
 go.sum       |   2 +
 ping.go      | 113 +++++++++++++++++++++++++++++++++++++++++++++++++++
 ping_test.go |  27 ++++++++++++
 4 files changed, 143 insertions(+)

diff --git a/go.mod b/go.mod
index 25bb5c0..8823331 100644
--- a/go.mod
+++ b/go.mod
@@ -5,6 +5,7 @@ go 1.25.6
 require (
 	github.com/gosnmp/gosnmp v1.43.2
 	golang.org/x/crypto v0.48.0
+	golang.org/x/net v0.50.0
 	google.golang.org/protobuf v1.36.11
 )
 
diff --git a/go.sum b/go.sum
index a8070f5..3fd0d3b 100644
--- a/go.sum
+++ b/go.sum
@@ -10,6 +10,8 @@ github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
 golang.org/x/crypto v0.48.0 h1:/VRzVqiRSggnhY7gNRxPauEQ5Drw9haKdM0jqfcCFts=
 golang.org/x/crypto v0.48.0/go.mod h1:r0kV5h3qnFPlQnBSrULhlsRfryS2pmewsg+XfMgkVos=
+golang.org/x/net v0.50.0 h1:ucWh9eiCGyDR3vtzso0WMQinm2Dnt8cFMuQa9K33J60=
+golang.org/x/net v0.50.0/go.mod h1:UgoSli3F/pBgdJBHCTc+tp3gmrU4XswgGRgtnwWTfyM=
 golang.org/x/sys v0.41.0 h1:Ivj+2Cp/ylzLiEU89QhWblYnOE9zerudt9Ftecq2C6k=
 golang.org/x/sys v0.41.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 golang.org/x/term v0.40.0 h1:36e4zGLqU4yhjlmxEaagx2KuYbJq3EwY8K943ZsHcvg=
diff --git a/ping.go b/ping.go
index e2fb60a..a2f4904 100644
--- a/ping.go
+++ b/ping.go
@@ -4,14 +4,127 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"os"
 	"os/exec"
 	"strconv"
 	"strings"
 	"time"
+
+	"golang.org/x/net/icmp"
+	"golang.org/x/net/ipv4"
+	"golang.org/x/net/ipv6"
 )
 
+// icmpPing sends a single ICMP echo request and returns the round-trip time in milliseconds.
+// Uses unprivileged UDP sockets where available, falling back to raw sockets.
+func icmpPing(ip string, timeoutMs int) (float64, error) {
+	parsedIP := net.ParseIP(ip)
+	if parsedIP == nil {
+		return 0, fmt.Errorf("invalid IP address: %s", ip)
+	}
+
+	isIPv4 := parsedIP.To4() != nil
+	var network string
+	var dst net.Addr
+	var msgType icmp.Type
+
+	if isIPv4 {
+		network = "udp4"
+		dst = &net.UDPAddr{IP: parsedIP}
+		msgType = ipv4.ICMPTypeEcho
+	} else {
+		network = "udp6"
+		dst = &net.UDPAddr{IP: parsedIP}
+		msgType = ipv6.ICMPTypeEchoRequest
+	}
+
+	conn, err := icmp.ListenPacket(network, "")
+	if err != nil {
+		return 0, &errICMPUnavailable{err: fmt.Errorf("icmp listen: %w", err)}
+	}
+	defer func() { _ = conn.Close() }()
+
+	id := os.Getpid() & 0xffff
+	msg := icmp.Message{
+		Type: msgType,
+		Code: 0,
+		Body: &icmp.Echo{
+			ID:   id,
+			Seq:  1,
+			Data: []byte("towerops"),
+		},
+	}
+
+	var proto int
+	if isIPv4 {
+		proto = 1 // ICMP
+	} else {
+		proto = 58 // ICMPv6
+	}
+
+	wb, err := msg.Marshal(nil)
+	if err != nil {
+		return 0, fmt.Errorf("icmp marshal: %w", err)
+	}
+
+	deadline := time.Now().Add(time.Duration(timeoutMs) * time.Millisecond)
+	if err := conn.SetDeadline(deadline); err != nil {
+		return 0, fmt.Errorf("set deadline: %w", err)
+	}
+
+	start := time.Now()
+	if _, err := conn.WriteTo(wb, dst); err != nil {
+		return 0, fmt.Errorf("icmp write: %w", err)
+	}
+
+	rb := make([]byte, 1500)
+	for {
+		n, _, err := conn.ReadFrom(rb)
+		if err != nil {
+			return 0, fmt.Errorf("icmp read: %w", err)
+		}
+		elapsed := time.Since(start)
+
+		rm, err := icmp.ParseMessage(proto, rb[:n])
+		if err != nil {
+			continue
+		}
+
+		switch rm.Type {
+		case ipv4.ICMPTypeEchoReply, ipv6.ICMPTypeEchoReply:
+			echo, ok := rm.Body.(*icmp.Echo)
+			if !ok || echo.ID != id {
+				continue
+			}
+			return float64(elapsed.Microseconds()) / 1000.0, nil
+		}
+	}
+}
+
+// errICMPUnavailable is returned when the ICMP socket can't be opened.
+// This triggers a fallback to exec-based ping.
+type errICMPUnavailable struct{ err error }
+
+func (e *errICMPUnavailable) Error() string { return e.err.Error() }
+
 // pingDevice pings an IP address and returns the response time in milliseconds.
+// Tries raw ICMP first for efficiency, falls back to exec-based ping only
+// if the system doesn't support unprivileged ICMP.
 func pingDevice(ip string, timeoutMs int) (float64, error) {
+	ms, err := icmpPing(ip, timeoutMs)
+	if err == nil {
+		return ms, nil
+	}
+
+	// Only fall back to exec if ICMP sockets aren't available
+	if _, ok := err.(*errICMPUnavailable); ok {
+		return execPing(ip, timeoutMs)
+	}
+	return 0, err
+}
+
+// execPing uses the system ping command as a fallback.
+func execPing(ip string, timeoutMs int) (float64, error) {
 	parsedIP := net.ParseIP(ip)
 	if parsedIP == nil {
 		return 0, fmt.Errorf("invalid IP address: %s", ip)
diff --git a/ping_test.go b/ping_test.go
index a5c5054..e5b2fb5 100644
--- a/ping_test.go
+++ b/ping_test.go
@@ -38,6 +38,33 @@ func TestPingDeviceIPv6(t *testing.T) {
 	}
 }
 
+func TestIcmpPingLocalhost(t *testing.T) {
+	ms, err := icmpPing("127.0.0.1", 5000)
+	if err != nil {
+		t.Skipf("ICMP not available: %v", err)
+	}
+	if ms <= 0 {
+		t.Errorf("expected positive response time, got %v", ms)
+	}
+}
+
+func TestIcmpPingIPv6(t *testing.T) {
+	ms, err := icmpPing("::1", 5000)
+	if err != nil {
+		t.Skipf("IPv6 ICMP not available: %v", err)
+	}
+	if ms <= 0 {
+		t.Errorf("expected positive response time, got %v", ms)
+	}
+}
+
+func TestIcmpPingInvalidIP(t *testing.T) {
+	_, err := icmpPing("not-an-ip", 5000)
+	if err == nil {
+		t.Error("expected error for invalid IP")
+	}
+}
+
 func TestParsePingTime(t *testing.T) {
 	tests := []struct {
 		name    string