Change the framing Encoder/Decoder to take the destination slice.

In theory this is easier on the garbage collector.  Probably could
reuse more of the intermediary buffers by stashing them in the
connection state, but that makes the code kind of messy.  This should
be an improvement.

3 files changed, 63 insertions, 67 deletions

diff --git a/framing/framing.go b/framing/framing.go
index 710bc1f..c57189d 100644
--- a/framing/framing.go
+++ b/framing/framing.go
@@ -61,6 +61,7 @@ import (
 	"errors"
 	"fmt"
 	"hash"
+	"io"
 
 	"code.google.com/p/go.crypto/nacl/secretbox"
 
@@ -172,40 +173,41 @@ func NewEncoder(key []byte) *Encoder {
 }
 
 // Encode encodes a single frame worth of payload and returns the encoded
-// length and the resulting frame.  InvalidPayloadLengthError is recoverable,
-// all other errors MUST be treated as fatal and the session aborted.
-func (encoder *Encoder) Encode(payload []byte) (int, []byte, error) {
+// length.  InvalidPayloadLengthError is recoverable, all other errors MUST be
+// treated as fatal and the session aborted.
+func (encoder *Encoder) Encode(frame, payload []byte) (n int, err error) {
 	payloadLen := len(payload)
 	if MaximumFramePayloadLength < payloadLen {
-		return 0, nil, InvalidPayloadLengthError(payloadLen)
+		return 0, InvalidPayloadLengthError(payloadLen)
+	}
+	if len(frame) < payloadLen + FrameOverhead {
+		return 0, io.ErrShortBuffer
 	}
 
 	// Generate a new nonce.
 	var nonce [nonceLength]byte
-	err := encoder.nonce.bytes(&nonce)
+	err = encoder.nonce.bytes(&nonce)
 	if err != nil {
-		return 0, nil, err
+		return 0, err
 	}
 	encoder.nonce.counter++
 
 	// Encrypt and MAC payload.
-	var box []byte
-	box = secretbox.Seal(nil, payload, &nonce, &encoder.key)
+	box := secretbox.Seal(frame[:lengthLength], payload, &nonce, &encoder.key)
 
 	// Obfuscate the length.
-	length := uint16(len(box))
+	length := uint16(len(box)-lengthLength)
 	encoder.sip.Write(nonce[:])
 	lengthMask := encoder.sip.Sum(nil)
 	encoder.sip.Reset()
 	length ^= binary.BigEndian.Uint16(lengthMask)
-	var obfsLen [lengthLength]byte
-	binary.BigEndian.PutUint16(obfsLen[:], length)
+	binary.BigEndian.PutUint16(frame[:2], length)
 
 	// Prepare the next obfsucator.
-	encoder.sip.Write(box)
+	encoder.sip.Write(box[lengthLength:])
 
 	// Return the frame.
-	return payloadLen + FrameOverhead, append(obfsLen[:], box...), nil
+	return len(box), nil
 }
 
 // Decoder is a frame decoder instance.
@@ -233,23 +235,23 @@ func NewDecoder(key []byte) *Decoder {
 	return decoder
 }
 
-// Decode decodes a stream of data and returns the length and decoded frame if
-// any.  ErrAgain is a temporary failure, all other errors MUST be treated as
-// fatal and the session aborted.
-func (decoder *Decoder) Decode(data *bytes.Buffer) (int, []byte, error) {
+// Decode decodes a stream of data and returns the length if any.  ErrAgain is
+// a temporary failure, all other errors MUST be treated as fatal and the
+// session aborted.
+func (decoder *Decoder) Decode(data []byte, frames *bytes.Buffer) (int, error) {
 	// A length of 0 indicates that we do not know how big the next frame is
 	// going to be.
 	if decoder.nextLength == 0 {
 		// Attempt to pull out the next frame length.
-		if lengthLength > data.Len() {
-			return 0, nil, ErrAgain
+		if lengthLength > frames.Len() {
+			return 0, ErrAgain
 		}
 
 		// Remove the length field from the buffer.
 		var obfsLen [lengthLength]byte
-		n, err := data.Read(obfsLen[:])
+		n, err := frames.Read(obfsLen[:])
 		if err != nil {
-			return 0, nil, err
+			return 0, err
 		} else if n != lengthLength {
 			// Should *NEVER* happen, since at least 2 bytes exist.
 			panic(fmt.Sprintf("BUG: Failed to read obfuscated length: %d", n))
@@ -258,7 +260,7 @@ func (decoder *Decoder) Decode(data *bytes.Buffer) (int, []byte, error) {
 		// Derive the nonce the peer used.
 		err = decoder.nonce.bytes(&decoder.nextNonce)
 		if err != nil {
-			return 0, nil, err
+			return 0, err
 		}
 
 		// Deobfuscate the length field.
@@ -268,36 +270,36 @@ func (decoder *Decoder) Decode(data *bytes.Buffer) (int, []byte, error) {
 		decoder.sip.Reset()
 		length ^= binary.BigEndian.Uint16(lengthMask)
 		if maxFrameLength < length || minFrameLength > length {
-			return 0, nil, InvalidFrameLengthError(length)
+			return 0, InvalidFrameLengthError(length)
 		}
 		decoder.nextLength = length
 	}
 
-	if int(decoder.nextLength) > data.Len() {
-		return 0, nil, ErrAgain
+	if int(decoder.nextLength) > frames.Len() {
+		return 0, ErrAgain
 	}
 
 	// Unseal the frame.
-	box := make([]byte, decoder.nextLength)
-	n, err := data.Read(box)
+	var box [maxFrameLength]byte
+	n, err := frames.Read(box[:decoder.nextLength])
 	if err != nil {
-		return 0, nil, err
+		return 0, err
 	} else if n != int(decoder.nextLength) {
-		// Should *NEVER* happen, since at least 2 bytes exist.
+		// Should *NEVER* happen, since the length is checked.
 		panic(fmt.Sprintf("BUG: Failed to read secretbox, got %d, should have %d",
 						  n, decoder.nextLength))
 	}
-	out, ok := secretbox.Open(nil, box, &decoder.nextNonce, &decoder.key)
+	out, ok := secretbox.Open(data[:0], box[:n], &decoder.nextNonce, &decoder.key)
 	if !ok {
-		return 0, nil, ErrTagMismatch
+		return 0, ErrTagMismatch
 	}
-	decoder.sip.Write(box)
+	decoder.sip.Write(box[:n])
 
 	// Clean up and prepare for the next frame.
 	decoder.nextLength = 0
 	decoder.nonce.counter++
 
-	return len(out), out, nil
+	return len(out), nil
 }
 
 /* vim :set ts=4 sw=4 sts=4 noet : */
diff --git a/framing/framing_test.go b/framing/framing_test.go
index 221ea5e..08f5f17 100644
--- a/framing/framing_test.go
+++ b/framing/framing_test.go
@@ -69,7 +69,8 @@ func TestEncoder_Encode(t *testing.T) {
 	buf := make([]byte, MaximumFramePayloadLength)
 	_, _ = rand.Read(buf) // YOLO
 	for i := 0; i <= MaximumFramePayloadLength; i++ {
-		n, frame, err := encoder.Encode(buf[0:i])
+		var frame [MaximumSegmentLength]byte
+		n, err := encoder.Encode(frame[:], buf[0:i])
 		if err != nil {
 			t.Fatalf("Encoder.encode([%d]byte), failed: %s", i, err)
 		}
@@ -77,10 +78,6 @@ func TestEncoder_Encode(t *testing.T) {
 			t.Fatalf("Unexpected encoded framesize: %d, expecting %d", n, i+
 				FrameOverhead)
 		}
-		if len(frame) != n {
-			t.Fatalf("Encoded frame length/rval mismatch: %d != %d",
-				len(frame), n)
-		}
 	}
 }
 
@@ -88,9 +85,10 @@ func TestEncoder_Encode(t *testing.T) {
 func TestEncoder_Encode_Oversize(t *testing.T) {
 	encoder := newEncoder(t)
 
-	buf := make([]byte, MaximumFramePayloadLength+1)
-	_, _ = rand.Read(buf) // YOLO
-	_, _, err := encoder.Encode(buf)
+	var frame [MaximumSegmentLength]byte
+	var buf [MaximumFramePayloadLength+1]byte
+	_, _ = rand.Read(buf[:]) // YOLO
+	_, err := encoder.Encode(frame[:], buf[:])
 	if _, ok := err.(InvalidPayloadLengthError); !ok {
 		t.Error("Encoder.encode() returned unexpected error:", err)
 	}
@@ -112,10 +110,11 @@ func TestDecoder_Decode(t *testing.T) {
 	encoder := NewEncoder(key)
 	decoder := NewDecoder(key)
 
-	buf := make([]byte, MaximumFramePayloadLength)
-	_, _ = rand.Read(buf) // YOLO
+	var buf [MaximumFramePayloadLength]byte
+	_, _ = rand.Read(buf[:]) // YOLO
 	for i := 0; i <= MaximumFramePayloadLength; i++ {
-		encLen, frame, err := encoder.Encode(buf[0:i])
+		var frame [MaximumSegmentLength]byte
+		encLen, err := encoder.Encode(frame[:], buf[0:i])
 		if err != nil {
 			t.Fatalf("Encoder.encode([%d]byte), failed: %s", i, err)
 		}
@@ -123,12 +122,10 @@ func TestDecoder_Decode(t *testing.T) {
 			t.Fatalf("Unexpected encoded framesize: %d, expecting %d", encLen,
 				i+FrameOverhead)
 		}
-		if len(frame) != encLen {
-			t.Fatalf("Encoded frame length/rval mismatch: %d != %d",
-				len(frame), encLen)
-		}
 
-		decLen, decoded, err := decoder.Decode(bytes.NewBuffer(frame))
+		var decoded [MaximumFramePayloadLength]byte
+
+		decLen, err := decoder.Decode(decoded[:], bytes.NewBuffer(frame[:encLen]))
 		if err != nil {
 			t.Fatalf("Decoder.decode([%d]byte), failed: %s", i, err)
 		}
@@ -136,13 +133,8 @@ func TestDecoder_Decode(t *testing.T) {
 			t.Fatalf("Unexpected decoded framesize: %d, expecting %d",
 				decLen, i)
 		}
-		if len(decoded) != i {
-			t.Fatalf("Encoded frame length/rval mismatch: %d != %d",
-				len(decoded), i)
-
-		}
 
-		if 0 != bytes.Compare(decoded, buf[0:i]) {
+		if 0 != bytes.Compare(decoded[:decLen], buf[:i]) {
 			t.Fatalf("Frame %d does not match encoder input", i)
 		}
 	}
@@ -152,6 +144,7 @@ func TestDecoder_Decode(t *testing.T) {
 // of payload.
 func BenchmarkEncoder_Encode(b *testing.B) {
 	var chopBuf [MaximumFramePayloadLength]byte
+	var frame [MaximumSegmentLength]byte
 	payload := make([]byte, 1024*1024)
 	encoder := NewEncoder(generateRandomKey())
 	b.ResetTimer()
@@ -165,8 +158,8 @@ func BenchmarkEncoder_Encode(b *testing.B) {
 				b.Fatal("buffer.Read() failed:", err)
 			}
 
-			n, frame, err := encoder.Encode(chopBuf[:n])
-			transfered += len(frame) - FrameOverhead
+			n, err = encoder.Encode(frame[:], chopBuf[:n])
+			transfered += n - FrameOverhead
 		}
 		if transfered != len(payload) {
 			b.Fatalf("Transfered length mismatch: %d != %d", transfered,
diff --git a/packet.go b/packet.go
index 339a86d..6f9eb03 100644
--- a/packet.go
+++ b/packet.go
@@ -100,18 +100,18 @@ func (c *Obfs4Conn) producePacket(w io.Writer, pktType uint8, data []byte, padLe
 	pktLen := packetOverhead + len(data) + int(padLen)
 
 	// Encode the packet in an AEAD frame.
-	// TODO: Change Encode to write into frame directly
-	var frame []byte
-	_, frame, err = c.encoder.Encode(pkt[:pktLen])
+	var frame [framing.MaximumSegmentLength]byte
+	frameLen := 0
+	frameLen, err = c.encoder.Encode(frame[:], pkt[:pktLen])
 	if err != nil {
 		// All encoder errors are fatal.
 		return
 	}
 	var wrLen int
-	wrLen, err = w.Write(frame)
+	wrLen, err = w.Write(frame[:frameLen])
 	if err != nil {
 		return
-	} else if wrLen < len(frame) {
+	} else if wrLen < frameLen {
 		err = io.ErrShortWrite
 		return
 	}
@@ -132,22 +132,23 @@ func (c *Obfs4Conn) consumeFramedPackets(w io.Writer) (n int, err error) {
 	}
 	c.receiveBuffer.Write(buf[:rdLen])
 
+	var decoded [framing.MaximumFramePayloadLength]byte
 	for c.receiveBuffer.Len() > 0 {
 		// Decrypt an AEAD frame.
-		// TODO: Change Decode to write into packet directly
-		var pkt []byte
-		_, pkt, err = c.decoder.Decode(&c.receiveBuffer)
+		decLen := 0
+		decLen, err = c.decoder.Decode(decoded[:], &c.receiveBuffer)
 		if err == framing.ErrAgain {
 			// The accumulated payload does not make up a full frame.
 			return
 		} else if err != nil {
 			break
-		} else if len(pkt) < packetOverhead {
-			err = InvalidPacketLengthError(len(pkt))
+		} else if decLen < packetOverhead {
+			err = InvalidPacketLengthError(decLen)
 			break
 		}
 
 		// Decode the packet.
+		pkt := decoded[0:decLen]
 		pktType := pkt[0]
 		payloadLen := binary.BigEndian.Uint16(pkt[1:])
 		if int(payloadLen) > len(pkt)-packetOverhead {