From: Matt Joiner <anacrolix@gmail.com>
Date: Mon, 4 Jan 2021 00:34:04 +0000 (+1100)
Subject: mse: Optimize allocations receiving handshakes
X-Git-Tag: v1.20.0~2
X-Git-Url: http://www.git.stargrave.org/?a=commitdiff_plain;h=be639852e393156e2a4dce9185e54ecc45aa7081;p=btrtrc.git

mse: Optimize allocations receiving handshakes
---

diff --git a/mse/mse.go b/mse/mse.go
index 85d55a7d..d4a0368e 100644
--- a/mse/mse.go
+++ b/mse/mse.go
@@ -19,7 +19,6 @@ import (
 	"sync"
 
 	"github.com/anacrolix/missinggo/perf"
-	"github.com/bradfitz/iter"
 )
 
 const (
@@ -286,18 +285,22 @@ func (h *handshake) postWrite(b []byte) error {
 	return nil
 }
 
-func xor(dst, src []byte) (ret []byte) {
-	max := len(dst)
-	if max > len(src) {
-		max = len(src)
-	}
-	ret = make([]byte, 0, max)
-	for i := range iter.N(max) {
-		ret = append(ret, dst[i]^src[i])
+func xor(a, b []byte) (ret []byte) {
+	max := len(a)
+	if max > len(b) {
+		max = len(b)
 	}
+	ret = make([]byte, max)
+	xorInPlace(ret, a, b)
 	return
 }
 
+func xorInPlace(dst, a, b []byte) {
+	for i := range dst {
+		dst[i] = a[i] ^ b[i]
+	}
+}
+
 func marshal(w io.Writer, data ...interface{}) (err error) {
 	for _, data := range data {
 		err = binary.Write(w, binary.BigEndian, data)
@@ -438,9 +441,17 @@ func (h *handshake) receiverSteps() (ret io.ReadWriter, chosen CryptoMethod, err
 	if err != nil {
 		return
 	}
+	expectedHash := hash(req3, h.s[:])
+	eachHash := sha1.New()
+	var sum, xored [sha1.Size]byte
 	err = ErrNoSecretKeyMatch
 	h.skeys(func(skey []byte) bool {
-		if bytes.Equal(xor(hash(req2, skey), hash(req3, h.s[:])), b[:]) {
+		eachHash.Reset()
+		eachHash.Write(req2)
+		eachHash.Write(skey)
+		eachHash.Sum(sum[:0])
+		xorInPlace(xored[:], sum[:], expectedHash)
+		if bytes.Equal(xored[:], b[:]) {
 			h.skey = skey
 			err = nil
 			return false