Add packet padding container for packet length shaping

common/packetPaddingContainer/container.go

@@ -0,0 +1,47 @@
+package packetPaddingContainer
+
+import "encoding/binary"
+
+func New() PacketPaddingContainer {
+	return packetPaddingContainer{}
+}
+
+type packetPaddingContainer struct {
+}
+
+func (c packetPaddingContainer) Pack(data_OWNERSHIP_RELINQUISHED []byte, padding int) []byte {
+	data := append(data_OWNERSHIP_RELINQUISHED, make([]byte, padding)...)
+	data_length := len(data_OWNERSHIP_RELINQUISHED)
+	data = append(data, byte(data_length>>8), byte(data_length))
+	return data
+}
+
+func (c packetPaddingContainer) Pad(padding int) []byte {
+	if assertPaddingLengthIsNotNegative := padding < 0; assertPaddingLengthIsNotNegative {
+		return nil
+	}
+	switch padding {
+	case 0:
+		return []byte{}
+	case 1:
+		return []byte{0}
+	case 2:
+		return []byte{0, 0}
+	default:
+		return append(make([]byte, padding-2), byte(padding>>8), byte(padding))
+	}
+
+}
+
+func (c packetPaddingContainer) Unpack(wrappedData_OWNERSHIP_RELINQUISHED []byte) ([]byte, int) {
+	if len(wrappedData_OWNERSHIP_RELINQUISHED) < 2 {
+		return nil, len(wrappedData_OWNERSHIP_RELINQUISHED)
+	}
+	wrappedData_tail := wrappedData_OWNERSHIP_RELINQUISHED[len(wrappedData_OWNERSHIP_RELINQUISHED)-2:]
+	dataLength := int(binary.BigEndian.Uint16(wrappedData_tail))
+	paddingLength := len(wrappedData_OWNERSHIP_RELINQUISHED) - dataLength - 2
+	if paddingLength < 0 {
+		return nil, paddingLength
+	}
+	return wrappedData_OWNERSHIP_RELINQUISHED[:dataLength], paddingLength
+}

common/packetPaddingContainer/containerIfce.go

@@ -0,0 +1,34 @@
+package packetPaddingContainer
+
+// PacketPaddingContainer is an interface that defines methods to pad packets
+// with a given number of bytes, and to unpack the padding from a padded packet.
+// The packet format is as follows if the desired output length is greater than
+// 2 bytes:
+// | data | padding | data length |
+// The data length is a 16-bit big-endian integer that represents the length of
+// the data in bytes.
+// If the desired output length is 2 bytes or less, the packet format is as
+// follows:
+// | padding |
+// No payload will be included in the packet.
+type PacketPaddingContainer interface {
+	// Pack pads the given data with the given number of bytes, and appends the
+	// length of the data to the end of the data. The returned byte slice
+	// contains the padded data.
+	// This generates a packet with a length of
+	// len(data_OWNERSHIP_RELINQUISHED) + padding + 2
+	// @param data_OWNERSHIP_RELINQUISHED - The payload, this reference is consumed and should not be used after this call.
+	// @param padding - The number of padding bytes to add to the data.
+	Pack(data_OWNERSHIP_RELINQUISHED []byte, padding int) []byte
+
+	// Unpack extracts the data and padding from the given padded data. It
+	// returns the data and the number of padding bytes.
+	// the data may be nil.
+	// @param wrappedData_OWNERSHIP_RELINQUISHED - The packet, this reference is consumed and should not be used after this call.
+	Unpack(wrappedData_OWNERSHIP_RELINQUISHED []byte) ([]byte, int)
+
+	// Pad returns a padding packet of padding length.
+	// If the padding length is less than 0, nil is returned.
+	// @param padding - The number of padding bytes to add to the data.
+	Pad(padding int) []byte
+}

common/packetPaddingContainer/container_test.go

@@ -0,0 +1,113 @@
+package packetPaddingContainer_test
+
+import (
+	"testing"
+
+	. "github.com/smartystreets/goconvey/convey"
+
+	"gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake/v2/common/packetPaddingContainer"
+)
+
+func TestPacketPaddingContainer(t *testing.T) {
+	Convey("Given a PacketPaddingContainer", t, func() {
+		container := packetPaddingContainer.New()
+
+		Convey("When packing data with padding", func() {
+			data := []byte("testdata")
+			padding := 4
+			packedData := container.Pack(data, padding)
+
+			Convey("The packed data should have the correct length", func() {
+				expectedLength := len(data) + padding + 2
+				So(len(packedData), ShouldEqual, expectedLength)
+			})
+
+			Convey("When unpacking the packed data", func() {
+				unpackedData, unpackedPadding := container.Unpack(packedData)
+
+				Convey("The unpacked data should match the original data", func() {
+					So(string(unpackedData), ShouldEqual, string(data))
+				})
+
+				Convey("The unpacked padding should match the original padding", func() {
+					So(unpackedPadding, ShouldEqual, padding)
+				})
+			})
+		})
+
+		Convey("When packing empty data with padding", func() {
+			data := []byte("")
+			padding := 4
+			packedData := container.Pack(data, padding)
+
+			Convey("The packed data should have the correct length", func() {
+				expectedLength := len(data) + padding + 2
+				So(len(packedData), ShouldEqual, expectedLength)
+			})
+
+			Convey("When unpacking the packed data", func() {
+				unpackedData, unpackedPadding := container.Unpack(packedData)
+
+				Convey("The unpacked data should match the original data", func() {
+					So(string(unpackedData), ShouldEqual, string(data))
+				})
+
+				Convey("The unpacked padding should match the original padding", func() {
+					So(unpackedPadding, ShouldEqual, padding)
+				})
+			})
+		})
+
+		Convey("When packing data with zero padding", func() {
+			data := []byte("testdata")
+			padding := 0
+			packedData := container.Pack(data, padding)
+
+			Convey("The packed data should have the correct length", func() {
+				expectedLength := len(data) + padding + 2
+				So(len(packedData), ShouldEqual, expectedLength)
+			})
+
+			Convey("When unpacking the packed data", func() {
+				unpackedData, unpackedPadding := container.Unpack(packedData)
+
+				Convey("The unpacked data should match the original data", func() {
+					So(string(unpackedData), ShouldEqual, string(data))
+				})
+
+				Convey("The unpacked padding should match the original padding", func() {
+					So(unpackedPadding, ShouldEqual, padding)
+				})
+			})
+		})
+
+		Convey("When padding data", func() {
+			Convey("With a positive padding length", func() {
+				padLength := 3
+				padData := container.Pad(padLength)
+
+				Convey("The padded data should have the correct length", func() {
+					So(len(padData), ShouldEqual, padLength)
+				})
+			})
+
+			Convey("With a zero padding length", func() {
+				padLength := 0
+				padData := container.Pad(padLength)
+
+				Convey("The padded data should be empty", func() {
+					So(len(padData), ShouldEqual, 0)
+				})
+			})
+
+			Convey("With a negative padding length", func() {
+				padLength := -1
+				padData := container.Pad(padLength)
+
+				Convey("The padded data should be nil", func() {
+					So(padData, ShouldBeNil)
+				})
+			})
+		})
+	})
+}