Add packet capture to debug bundle and CLI

util/capture/pcap_test.go

@@ -0,0 +1,68 @@
+package capture
+
+import (
+	"bytes"
+	"encoding/binary"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestPcapWriter_GlobalHeader(t *testing.T) {
+	var buf bytes.Buffer
+	pw := NewPcapWriter(&buf, 0)
+
+	// Header is lazy, so write a dummy packet to trigger it.
+	err := pw.WritePacket(time.Now(), []byte{0x45, 0, 0, 20, 0, 0, 0, 0, 64, 1, 0, 0, 10, 0, 0, 1, 10, 0, 0, 2})
+	require.NoError(t, err)
+
+	data := buf.Bytes()
+	require.GreaterOrEqual(t, len(data), 24, "should contain global header")
+
+	assert.Equal(t, uint32(pcapMagic), binary.LittleEndian.Uint32(data[0:4]), "magic number")
+	assert.Equal(t, uint16(pcapVersionMaj), binary.LittleEndian.Uint16(data[4:6]), "version major")
+	assert.Equal(t, uint16(pcapVersionMin), binary.LittleEndian.Uint16(data[6:8]), "version minor")
+	assert.Equal(t, uint32(defaultSnapLen), binary.LittleEndian.Uint32(data[16:20]), "snap length")
+	assert.Equal(t, uint32(linkTypeRaw), binary.LittleEndian.Uint32(data[20:24]), "link type")
+}
+
+func TestPcapWriter_WritePacket(t *testing.T) {
+	var buf bytes.Buffer
+	pw := NewPcapWriter(&buf, 100)
+
+	ts := time.Date(2025, 6, 15, 12, 30, 45, 123456000, time.UTC)
+	payload := make([]byte, 50)
+	for i := range payload {
+		payload[i] = byte(i)
+	}
+
+	err := pw.WritePacket(ts, payload)
+	require.NoError(t, err)
+
+	data := buf.Bytes()[24:] // skip global header
+	require.Len(t, data, 16+50, "packet header + payload")
+
+	assert.Equal(t, uint32(ts.Unix()), binary.LittleEndian.Uint32(data[0:4]), "timestamp seconds")
+	assert.Equal(t, uint32(123456), binary.LittleEndian.Uint32(data[4:8]), "timestamp microseconds")
+	assert.Equal(t, uint32(50), binary.LittleEndian.Uint32(data[8:12]), "included length")
+	assert.Equal(t, uint32(50), binary.LittleEndian.Uint32(data[12:16]), "original length")
+	assert.Equal(t, payload, data[16:], "packet data")
+}
+
+func TestPcapWriter_SnapLen(t *testing.T) {
+	var buf bytes.Buffer
+	pw := NewPcapWriter(&buf, 10)
+
+	ts := time.Now()
+	payload := make([]byte, 50)
+
+	err := pw.WritePacket(ts, payload)
+	require.NoError(t, err)
+
+	data := buf.Bytes()[24:]
+	assert.Equal(t, uint32(10), binary.LittleEndian.Uint32(data[8:12]), "included length should be truncated")
+	assert.Equal(t, uint32(50), binary.LittleEndian.Uint32(data[12:16]), "original length preserved")
+	assert.Len(t, data[16:], 10, "only snap_len bytes written")
+}