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Remove unnecessary allocations in HopData encode/decode methods #26

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Remove unnecessary allocations in HopData encode/decode methods #26

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97 changes: 26 additions & 71 deletions sphinx.go
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,8 @@ import (
"crypto/hmac"
"crypto/sha256"
"encoding/binary"
"errors"
"io"
"io/ioutil"
"math/big"

"github.com/aead/chacha20"
Expand Down Expand Up @@ -146,62 +146,33 @@ type HopData struct {
HMAC [hmacSize]byte
}

// Encode writes the serialized version of the target HopData into the passed
// io.Writer.
func (hd *HopData) Encode(w io.Writer) error {
if _, err := w.Write([]byte{hd.Realm}); err != nil {
return err
}

if _, err := w.Write(hd.NextAddress[:]); err != nil {
return err
}

if err := binary.Write(w, binary.BigEndian, hd.ForwardAmount); err != nil {
return err
}

if err := binary.Write(w, binary.BigEndian, hd.OutgoingCltv); err != nil {
return err
// Encode writes the serialized version of the target HopData into the slice.
func (hd *HopData) Encode(dst []byte) error {
if len(dst) < hopDataSize {
errors.New("destination is too small")
}

if _, err := w.Write(paddingBytes[:]); err != nil {
return err
}

if _, err := w.Write(hd.HMAC[:]); err != nil {
return err
}
dst[0] = hd.Realm
copy(dst[1:], hd.NextAddress[:])
binary.BigEndian.PutUint64(dst[1+addressSize:], hd.ForwardAmount)
binary.BigEndian.PutUint32(dst[1+addressSize+8:], hd.OutgoingCltv)
copy(dst[hopDataSize-hmacSize-padSize:], paddingBytes[:])
copy(dst[hopDataSize-hmacSize:], hd.HMAC[:])

return nil
}

// Decode deserializes the encoded HopData contained int he passed io.Reader
// instance to the target empty HopData instance.
func (hd *HopData) Decode(r io.Reader) error {
if _, err := io.ReadFull(r, []byte{hd.Realm}); err != nil {
return err
}

if _, err := io.ReadFull(r, hd.NextAddress[:]); err != nil {
return err
}

if err := binary.Read(r, binary.BigEndian, &hd.ForwardAmount); err != nil {
return err
}

if err := binary.Read(r, binary.BigEndian, &hd.OutgoingCltv); err != nil {
return err
}

if _, err := io.CopyN(ioutil.Discard, r, padSize); err != nil {
return err
// Decode deserializes the encoded HopData contained in the passed slice.
func (hd *HopData) Decode(src []byte) error {
if len(src) < hopDataSize {
errors.New("source is too small")
}

if _, err := io.ReadFull(r, hd.HMAC[:]); err != nil {
return err
}
hd.Realm = src[0]
copy(hd.NextAddress[:], src[1:])
hd.ForwardAmount = binary.BigEndian.Uint64(src[1+addressSize:])
hd.OutgoingCltv = binary.BigEndian.Uint32(src[1+addressSize+8:])
copy(hd.HMAC[:], src[hopDataSize-hmacSize:])

return nil
}
Expand Down Expand Up @@ -292,9 +263,8 @@ func NewOnionPacket(paymentPath []*btcec.PublicKey, sessionKey *btcec.PrivateKey
// Allocate zero'd out byte slices to store the final mix header packet
// and the hmac for each hop.
var (
mixHeader [routingInfoSize]byte
nextHmac [hmacSize]byte
hopDataBuf bytes.Buffer
mixHeader [routingInfoSize]byte
nextHmac [hmacSize]byte
)

// Now we compute the routing information for each hop, along with a
Expand All @@ -317,17 +287,16 @@ func NewOnionPacket(paymentPath []*btcec.PublicKey, sessionKey *btcec.PrivateKey
streamBytes := generateCipherStream(rhoKey, numStreamBytes)

// Before we assemble the packet, we'll shift the current
// mix-header to the write in order to make room for this next
// mix-header to the right in order to make room for this next
// per-hop data.
rightShift(mixHeader[:], hopDataSize)
copy(mixHeader[hopDataSize:], mixHeader[:routingInfoSize-hopDataSize])

// With the mix header right-shifted, we'll encode the current
// hop data into a buffer we'll re-use during the packet
// construction.
if err := hopsData[i].Encode(&hopDataBuf); err != nil {
if err := hopsData[i].Encode(mixHeader[:]); err != nil {
return nil, err
}
copy(mixHeader[:], hopDataBuf.Bytes())

// Once the packet for this hop has been assembled, we'll
// re-encrypt the packet by XOR'ing with a stream of bytes
Expand All @@ -346,8 +315,6 @@ func NewOnionPacket(paymentPath []*btcec.PublicKey, sessionKey *btcec.PrivateKey
// prevent replay attacks.
packet := append(mixHeader[:], assocData...)
nextHmac = calcMac(muKey, packet)

hopDataBuf.Reset()
}

return &OnionPacket{
Expand All @@ -358,18 +325,6 @@ func NewOnionPacket(paymentPath []*btcec.PublicKey, sessionKey *btcec.PrivateKey
}, nil
}

// Shift the byte-slice by the given number of bytes to the right and 0-fill
// the resulting gap.
func rightShift(slice []byte, num int) {
for i := len(slice) - num - 1; i >= 0; i-- {
slice[num+i] = slice[i]
}

for i := 0; i < num; i++ {
slice[i] = 0
}
}

// generateHeaderPadding derives the bytes for padding the mix header to ensure
// it remains fixed sized throughout route transit. At each step, we add
// 'hopSize' padding of zeroes, concatenate it to the previous filler, then
Expand Down Expand Up @@ -763,7 +718,7 @@ func processOnionPacket(onionPkt *OnionPacket,
// out the per-hop data so we can derive the specified forwarding
// instructions.
var hopData HopData
if err := hopData.Decode(bytes.NewReader(hopInfo[:])); err != nil {
if err := hopData.Decode(hopInfo[:]); err != nil {
return nil, err
}

Expand Down