Making pcapgo Writer routine safe

pcapgo/write.go

@@ -10,6 +10,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
+	"sync"
 	"time"
 
 	"github.com/google/gopacket"
@@ -27,6 +28,8 @@ type Writer struct {
 	tsScaler int
 	// Moving this into the struct seems to save an allocation for each call to writePacketHeader
 	buf [16]byte
+	// Make sure our writer is routine safe
+	writeLock sync.Mutex
 }
 
 const magicMicroseconds = 0xA1B2C3D4
@@ -38,18 +41,18 @@ const versionMinor = 4
 // an append), you must call WriteFileHeader before WritePacket.  Packet
 // timestamps are written with nanosecond precision.
 //
-//  // Write a new file:
-//  f, _ := os.Create("/tmp/file.pcap")
-//  w := pcapgo.NewWriterNanos(f)
-//  w.WriteFileHeader(65536, layers.LinkTypeEthernet)  // new file, must do this.
-//  w.WritePacket(gopacket.CaptureInfo{...}, data1)
-//  f.Close()
-//  // Append to existing file (must have same snaplen and linktype)
-//  f2, _ := os.OpenFile("/tmp/fileNano.pcap", os.O_APPEND, 0700)
-//  w2 := pcapgo.NewWriter(f2)
-//  // no need for file header, it's already written.
-//  w2.WritePacket(gopacket.CaptureInfo{...}, data2)
-//  f2.Close()
+//	// Write a new file:
+//	f, _ := os.Create("/tmp/file.pcap")
+//	w := pcapgo.NewWriterNanos(f)
+//	w.WriteFileHeader(65536, layers.LinkTypeEthernet)  // new file, must do this.
+//	w.WritePacket(gopacket.CaptureInfo{...}, data1)
+//	f.Close()
+//	// Append to existing file (must have same snaplen and linktype)
+//	f2, _ := os.OpenFile("/tmp/fileNano.pcap", os.O_APPEND, 0700)
+//	w2 := pcapgo.NewWriter(f2)
+//	// no need for file header, it's already written.
+//	w2.WritePacket(gopacket.CaptureInfo{...}, data2)
+//	f2.Close()
 func NewWriterNanos(w io.Writer) *Writer {
 	return &Writer{w: w, tsScaler: nanosPerNano}
 }
@@ -59,18 +62,18 @@ func NewWriterNanos(w io.Writer) *Writer {
 // an append), you must call WriteFileHeader before WritePacket.
 // Packet timestamps are written witn microsecond precision.
 //
-//  // Write a new file:
-//  f, _ := os.Create("/tmp/file.pcap")
-//  w := pcapgo.NewWriter(f)
-//  w.WriteFileHeader(65536, layers.LinkTypeEthernet)  // new file, must do this.
-//  w.WritePacket(gopacket.CaptureInfo{...}, data1)
-//  f.Close()
-//  // Append to existing file (must have same snaplen and linktype)
-//  f2, _ := os.OpenFile("/tmp/file.pcap", os.O_APPEND, 0700)
-//  w2 := pcapgo.NewWriter(f2)
-//  // no need for file header, it's already written.
-//  w2.WritePacket(gopacket.CaptureInfo{...}, data2)
-//  f2.Close()
+//	// Write a new file:
+//	f, _ := os.Create("/tmp/file.pcap")
+//	w := pcapgo.NewWriter(f)
+//	w.WriteFileHeader(65536, layers.LinkTypeEthernet)  // new file, must do this.
+//	w.WritePacket(gopacket.CaptureInfo{...}, data1)
+//	f.Close()
+//	// Append to existing file (must have same snaplen and linktype)
+//	f2, _ := os.OpenFile("/tmp/file.pcap", os.O_APPEND, 0700)
+//	w2 := pcapgo.NewWriter(f2)
+//	// no need for file header, it's already written.
+//	w2.WritePacket(gopacket.CaptureInfo{...}, data2)
+//	f2.Close()
 func NewWriter(w io.Writer) *Writer {
 	return &Writer{w: w, tsScaler: nanosPerMicro}
 }
@@ -115,6 +118,8 @@ func (w *Writer) writePacketHeader(ci gopacket.CaptureInfo) error {
 
 // WritePacket writes the given packet data out to the file.
 func (w *Writer) WritePacket(ci gopacket.CaptureInfo, data []byte) error {
+	w.writeLock.Lock()
+	defer w.writeLock.Unlock()
 	if ci.CaptureLength != len(data) {
 		return fmt.Errorf("capture length %d does not match data length %d", ci.CaptureLength, len(data))
 	}