From 1073d0a2672bef736dc6ef76205085c16d68ee83 Mon Sep 17 00:00:00 2001
From: Ian Gulliver <github@flamingcow.io>
Date: Fri, 28 Nov 2025 15:28:47 -0800
Subject: [PATCH] Add LLDP packet capture and logging

---
 go.mod      |  4 ++++
 go.sum      | 16 ++++++++++++++++
 tendrils.go | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 67 insertions(+), 1 deletion(-)
 create mode 100644 go.sum

diff --git a/go.mod b/go.mod
index 13b8237..2198ae6 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,7 @@
 module github.com/gopatchy/tendrils
 
 go 1.24.4
+
+require github.com/google/gopacket v1.1.19
+
+require golang.org/x/sys v0.0.0-20190412213103-97732733099d // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..a915606
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,16 @@
+github.com/google/gopacket v1.1.19 h1:ves8RnFZPGiFnTS0uPQStjwru6uO6h+nlr9j6fL7kF8=
+github.com/google/gopacket v1.1.19/go.mod h1:iJ8V8n6KS+z2U1A8pUwu8bW5SyEMkXJB8Yo/Vo+TKTo=
+golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
+golang.org/x/crypto v0.0.0-20191011191535-87dc89f01550/go.mod h1:yigFU9vqHzYiE8UmvKecakEJjdnWj3jj499lnFckfCI=
+golang.org/x/lint v0.0.0-20200302205851-738671d3881b/go.mod h1:3xt1FjdF8hUf6vQPIChWIBhFzV8gjjsPE/fR3IyQdNY=
+golang.org/x/mod v0.1.1-0.20191105210325-c90efee705ee/go.mod h1:QqPTAvyqsEbceGzBzNggFXnrqF1CaUcvgkdR5Ot7KZg=
+golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859 h1:R/3boaszxrf1GEUWTVDzSKVwLmSJpwZ1yqXm8j0v2QI=
+golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
+golang.org/x/sync v0.0.0-20190423024810-112230192c58/go.mod h1:RxMgew5VJxzue5/jJTE5uejpjVlOe/izrB70Jof72aM=
+golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d h1:+R4KGOnez64A81RvjARKc4UT5/tI9ujCIVX+P5KiHuI=
+golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+golang.org/x/tools v0.0.0-20200130002326-2f3ba24bd6e7/go.mod h1:TB2adYChydJhpapKDTa4BR/hXlZSLoq2Wpct/0txZ28=
+golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/tendrils.go b/tendrils.go
index 545051e..c2eb8fb 100644
--- a/tendrils.go
+++ b/tendrils.go
@@ -2,9 +2,14 @@ package tendrils
 
 import (
 	"context"
+	"fmt"
 	"log"
 	"net"
 	"time"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	"github.com/google/gopacket/pcap"
 )
 
 type Tendrils struct {
@@ -89,5 +94,46 @@ func (t *Tendrils) updateGoroutines(interfaces []net.Interface) {
 }
 
 func (t *Tendrils) handleInterface(ctx context.Context, iface net.Interface) {
-	<-ctx.Done()
+	handle, err := pcap.OpenLive(iface.Name, 65536, true, 5*time.Second)
+	if err != nil {
+		log.Printf("[ERROR] failed to open interface %s: %v", iface.Name, err)
+		return
+	}
+	defer handle.Close()
+
+	bpfFilter := fmt.Sprintf("ether proto 0x88cc")
+	if err := handle.SetBPFFilter(bpfFilter); err != nil {
+		log.Printf("[ERROR] failed to set BPF filter on %s: %v", iface.Name, err)
+		return
+	}
+
+	packetSource := gopacket.NewPacketSource(handle, handle.LinkType())
+	packets := packetSource.Packets()
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case packet, ok := <-packets:
+			if !ok {
+				return
+			}
+			t.handleLLDPPacket(iface.Name, packet)
+		}
+	}
+}
+
+func (t *Tendrils) handleLLDPPacket(ifaceName string, packet gopacket.Packet) {
+	lldpLayer := packet.Layer(layers.LayerTypeLinkLayerDiscovery)
+	if lldpLayer == nil {
+		return
+	}
+
+	lldp, ok := lldpLayer.(*layers.LinkLayerDiscovery)
+	if !ok {
+		return
+	}
+
+	log.Printf("[%s] lldp packet received: ChassisID=%x PortID=%s TTL=%d",
+		ifaceName, lldp.ChassisID.ID, lldp.PortID.ID, lldp.TTL)
 }