UDP noise (#3711)

* added udp noise

* adding protobuf settings

* freedom json parser and clean up

* resolve confict

* fix and clean up

* use net.conn instead of packetconnwrapper

* avoid constructing SequentialWriter directly

---------

Co-authored-by: mmmray <142015632+mmmray@users.noreply.github.com>

proxy/freedom/freedom.go

@@ -208,6 +208,16 @@ func (h *Handler) Process(ctx context.Context, link *transport.Link, dialer inte
 			}
 		} else {
 			writer = NewPacketWriter(conn, h, ctx, UDPOverride)
+			if h.config.Noise != nil {
+				errors.LogDebug(ctx, "NOISE", h.config.Noise.StrNoise, h.config.Noise.LengthMin, h.config.Noise.LengthMax,
+					h.config.Noise.DelayMin, h.config.Noise.DelayMax)
+				writer = &NoisePacketWriter{
+					Writer:      writer,
+					noise:       h.config.Noise,
+					firstWrite:  true,
+					UDPOverride: UDPOverride,
+				}
+			}
 		}
 
 		if err := buf.Copy(input, writer, buf.UpdateActivity(timer)); err != nil {
@@ -329,6 +339,7 @@ func NewPacketWriter(conn net.Conn, h *Handler, ctx context.Context, UDPOverride
 			UDPOverride: UDPOverride,
 			Conn:        iConn,
 		}
+
 	}
 	return &buf.SequentialWriter{Writer: conn}
 }
@@ -385,6 +396,45 @@ func (w *PacketWriter) WriteMultiBuffer(mb buf.MultiBuffer) error {
 	return nil
 }
 
+type NoisePacketWriter struct {
+	buf.Writer
+	noise       *Noise
+	firstWrite  bool
+	UDPOverride net.Destination
+}
+
+// MultiBuffer writer with Noise in first packet
+func (w *NoisePacketWriter) WriteMultiBuffer(mb buf.MultiBuffer) error {
+	if w.firstWrite {
+		w.firstWrite = false
+		//Do not send Noise for dns requests(just to be safe)
+		if w.UDPOverride.Port == 53 {
+			return w.Writer.WriteMultiBuffer(mb)
+		}
+		var noise []byte
+		var err error
+		//User input string
+		if w.noise.StrNoise != "" {
+			noise = []byte(w.noise.StrNoise)
+		} else {
+			//Random noise
+			noise, err = GenerateRandomBytes(randBetween(int64(w.noise.LengthMin),
+				int64(w.noise.LengthMax)))
+		}
+
+		if err != nil {
+			return err
+		}
+		w.Writer.WriteMultiBuffer(buf.MultiBuffer{buf.FromBytes(noise)})
+
+		if w.noise.DelayMin != 0 {
+			time.Sleep(time.Duration(randBetween(int64(w.noise.DelayMin), int64(w.noise.DelayMax))) * time.Millisecond)
+		}
+
+	}
+	return w.Writer.WriteMultiBuffer(mb)
+}
+
 type FragmentWriter struct {
 	fragment *Fragment
 	writer   io.Writer
@@ -471,3 +521,13 @@ func randBetween(left int64, right int64) int64 {
 	bigInt, _ := rand.Int(rand.Reader, big.NewInt(right-left))
 	return left + bigInt.Int64()
 }
+func GenerateRandomBytes(n int64) ([]byte, error) {
+	b := make([]byte, n)
+	_, err := rand.Read(b)
+	// Note that err == nil only if we read len(b) bytes.
+	if err != nil {
+		return nil, err
+	}
+
+	return b, nil
+}