tracker/udp.go      | 27 +++++++++++++++++++++++++++
 tracker/udp_test.go | 20 ++++++++++++++++++++

diff --git a/tracker/udp.go b/tracker/udp.go
new file mode 100644
index 0000000000000000000000000000000000000000..55e9ad37d5b84736d1a11338e07c61e96d8c88e1
--- /dev/null
+++ b/tracker/udp.go
@@ -0,0 +1,27 @@
+package tracker
+
+type UDPConnectionRequest struct {
+	ConnectionId int64
+	Action       int32
+	TransctionId int32
+}
+
+type UDPAnnounceResponseHeader struct {
+	Action        int32
+	TransactionId int32
+	Interval      int32
+	Leechers      int32
+	Seeders       int32
+}
+
+type UDPAnnounceResponse struct {
+	UDPAnnounceResponseHeader
+	PeerAddrSlice
+}
+
+type PeerAddr struct {
+	IP   int32
+	Port int16
+}
+
+type PeerAddrSlice []PeerAddr
diff --git a/tracker/udp_test.go b/tracker/udp_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..cf4c0e01336eba92340bf7a4a3fe2f432950358c
--- /dev/null
+++ b/tracker/udp_test.go
@@ -0,0 +1,20 @@
+package tracker
+
+import (
+	"bytes"
+	"encoding/binary"
+	"testing"
+)
+
+func TestMarshalUDPAnnounceResponse(t *testing.T) {
+	w := bytes.NewBuffer(nil)
+	if err := binary.Write(w, binary.BigEndian, &PeerAddrSlice{{1, 2}, {3, 4}}); err != nil {
+		t.Fatalf("error writing udp announce response addrs: %s", err)
+	}
+	if w.String() != "\x00\x00\x00\x01\x00\x02\x00\x00\x00\x03\x00\x04" {
+		t.FailNow()
+	}
+	if binary.Size(UDPAnnounceResponseHeader{}) != 20 {
+		t.FailNow()
+	}
+}