fix: prevent data corruption in multiPacketListener by avoiding buf…

…fer resizing (#213)

* Add regression test that covers the issue.

* Fix the test.

* Use consistent comments.

service/listeners.go

@@ -288,10 +288,10 @@ func (m *multiPacketListener) Acquire() (net.PacketConn, error) {
  buffer := make([]byte, serverUDPBufferSize)
  for {
  n, addr, err := m.pc.ReadFrom(buffer)
- buffer = buffer[:n]
+ pkt := buffer[:n]
  select {
  case req := <-m.readCh:
- n := copy(req.buffer, buffer)
+ n := copy(req.buffer, pkt)
  req.respCh <- struct {
  n int
  addr net.Addr

service/listeners_test.go

@@ -142,6 +142,33 @@ func TestListenerManagerPacketListenerCreatesListenerOnDemand(t *testing.T) {
  <-done
 }
 
+func TestMultiPacketListener_SequentialReads(t *testing.T) {
+ m := NewListenerManager()
+ conn, err := m.ListenPacket("127.0.0.1:0")
+ require.NoError(t, err)
+ udpConn, err := net.Dial("udp", conn.LocalAddr().String())
+ require.NoError(t, err)
+
+ // Send and receive the first packet.
+ data1 := []byte("hello")
+ _, err = udpConn.Write(data1)
+ require.NoError(t, err)
+ received1 := make([]byte, serverUDPBufferSize)
+ n1, _, err := conn.ReadFrom(received1)
+ require.NoError(t, err)
+
+ // Send and receive a second larger packet.
+ data2 := []byte("a longer message than the first one")
+ _, err = udpConn.Write(data2)
+ require.NoError(t, err)
+ received2 := make([]byte, serverUDPBufferSize)
+ n2, _, err := conn.ReadFrom(received2)
+ require.NoError(t, err)
+
+ require.Equal(t, string(data1), string(received1[:n1]))
+ require.Equal(t, string(data2), string(received2[:n2]))
+}
+
 func BenchmarkMultiStreamListener_Acquire(b *testing.B) {
  lm := NewListenerManager()