Set the connection.cryptoMethod

It was unwittingly dropped from received connections, and may never have been set for initiated connections.

client.go

@@ -748,7 +748,7 @@ func (cl *Client) incomingPeerPort() int {
 func (cl *Client) initiateHandshakes(c *connection, t *Torrent) (ok bool, err error) {
 	if c.headerEncrypted {
 		var rw io.ReadWriter
-		rw, err = mse.InitiateHandshake(
+		rw, c.cryptoMethod, err = mse.InitiateHandshake(
 			struct {
 				io.Reader
 				io.Writer

handshake.go

@@ -187,7 +187,7 @@ func handleEncryption(
 		}
 	}
 	headerEncrypted = true
-	ret, err = mse.ReceiveHandshake(rw, skeys, func(provides mse.CryptoMethod) mse.CryptoMethod {
+	ret, cryptoMethod, err = mse.ReceiveHandshake(rw, skeys, func(provides mse.CryptoMethod) mse.CryptoMethod {
 		switch {
 		case policy.ForceEncryption:
 			return mse.CryptoMethodRC4

mse/mse.go

@@ -367,7 +367,7 @@ func (h *handshake) newEncrypt(initer bool) *rc4.Cipher {
 	return newEncrypt(initer, h.s[:], h.skey)
 }
 
-func (h *handshake) initerSteps() (ret io.ReadWriter, err error) {
+func (h *handshake) initerSteps() (ret io.ReadWriter, selected CryptoMethod, err error) {
 	h.postWrite(hash(req1, h.s[:]))
 	h.postWrite(xor(hash(req2, h.skey), hash(req3, h.s[:])))
 	buf := &bytes.Buffer{}
@@ -409,7 +409,8 @@ func (h *handshake) initerSteps() (ret io.ReadWriter, err error) {
 	if err != nil {
 		return
 	}
-	switch method & h.cryptoProvides {
+	selected = method & h.cryptoProvides
+	switch selected {
 	case CryptoMethodRC4:
 		ret = readWriter{r, &cipherWriter{e, h.conn, nil}}
 	case CryptoMethodPlaintext:
@@ -422,7 +423,7 @@ func (h *handshake) initerSteps() (ret io.ReadWriter, err error) {
 
 var ErrNoSecretKeyMatch = errors.New("no skey matched")
 
-func (h *handshake) receiverSteps() (ret io.ReadWriter, err error) {
+func (h *handshake) receiverSteps() (ret io.ReadWriter, chosen CryptoMethod, err error) {
 	// There is up to 512 bytes of padding, then the 20 byte hash.
 	err = readUntil(io.LimitReader(h.conn, 532), hash(req1, h.s[:]))
 	if err != nil {
@@ -460,7 +461,7 @@ func (h *handshake) receiverSteps() (ret io.ReadWriter, err error) {
 		return
 	}
 	cryptoProvidesCount.Add(strconv.FormatUint(uint64(provides), 16), 1)
-	chosen := h.chooseMethod(provides)
+	chosen = h.chooseMethod(provides)
 	_, err = io.CopyN(ioutil.Discard, r, int64(padLen))
 	if err != nil {
 		return
@@ -499,7 +500,7 @@ func (h *handshake) receiverSteps() (ret io.ReadWriter, err error) {
 	return
 }
 
-func (h *handshake) Do() (ret io.ReadWriter, err error) {
+func (h *handshake) Do() (ret io.ReadWriter, method CryptoMethod, err error) {
 	h.writeCond.L = &h.writeMu
 	h.writerCond.L = &h.writerMu
 	go h.writer()
@@ -521,14 +522,14 @@ func (h *handshake) Do() (ret io.ReadWriter, err error) {
 		return
 	}
 	if h.initer {
-		ret, err = h.initerSteps()
+		ret, method, err = h.initerSteps()
 	} else {
-		ret, err = h.receiverSteps()
+		ret, method, err = h.receiverSteps()
 	}
 	return
 }
 
-func InitiateHandshake(rw io.ReadWriter, skey []byte, initialPayload []byte, cryptoProvides CryptoMethod) (ret io.ReadWriter, err error) {
+func InitiateHandshake(rw io.ReadWriter, skey []byte, initialPayload []byte, cryptoProvides CryptoMethod) (ret io.ReadWriter, method CryptoMethod, err error) {
 	h := handshake{
 		conn:           rw,
 		initer:         true,
@@ -539,7 +540,7 @@ func InitiateHandshake(rw io.ReadWriter, skey []byte, initialPayload []byte, cry
 	return h.Do()
 }
 
-func ReceiveHandshake(rw io.ReadWriter, skeys SecretKeyIter, selectCrypto CryptoSelector) (ret io.ReadWriter, err error) {
+func ReceiveHandshake(rw io.ReadWriter, skeys SecretKeyIter, selectCrypto CryptoSelector) (ret io.ReadWriter, method CryptoMethod, err error) {
 	h := handshake{
 		conn:         rw,
 		initer:       false,

mse/mse_test.go

@@ -12,6 +12,7 @@ import (
 
 	_ "github.com/anacrolix/envpprof"
 	"github.com/bradfitz/iter"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -64,11 +65,9 @@ func handshakeTest(t testing.TB, ia []byte, aData, bData string, cryptoProvides
 	wg.Add(2)
 	go func() {
 		defer wg.Done()
-		a, err := InitiateHandshake(a, []byte("yep"), ia, cryptoProvides)
+		a, cm, err := InitiateHandshake(a, []byte("yep"), ia, cryptoProvides)
-		if err != nil {
+		require.NoError(t, err)
-			t.Fatal(err)
+		assert.Equal(t, cryptoSelect(cryptoProvides), cm)
-			return
-		}
 		go a.Write([]byte(aData))
 
 		var msg [20]byte
@@ -80,11 +79,9 @@ func handshakeTest(t testing.TB, ia []byte, aData, bData string, cryptoProvides
 	}()
 	go func() {
 		defer wg.Done()
-		b, err := ReceiveHandshake(b, sliceIter([][]byte{[]byte("nope"), []byte("yep"), []byte("maybe")}), cryptoSelect)
+		b, cm, err := ReceiveHandshake(b, sliceIter([][]byte{[]byte("nope"), []byte("yep"), []byte("maybe")}), cryptoSelect)
-		if err != nil {
+		require.NoError(t, err)
-			t.Fatal(err)
+		assert.Equal(t, cryptoSelect(cryptoProvides), cm)
-			return
-		}
 		go b.Write([]byte(bData))
 		// Need to be exact here, as there are several reads, and net.Pipe is
 		// most synchronous.
@@ -134,7 +131,7 @@ func (tr *trackReader) Read(b []byte) (n int, err error) {
 
 func TestReceiveRandomData(t *testing.T) {
 	tr := trackReader{rand.Reader, 0}
-	_, err := ReceiveHandshake(readWriter{&tr, ioutil.Discard}, nil, DefaultCryptoSelector)
+	_, _, err := ReceiveHandshake(readWriter{&tr, ioutil.Discard}, nil, DefaultCryptoSelector)
 	// No skey matches
 	require.Error(t, err)
 	// Establishing S, and then reading the maximum padding for giving up on
@@ -183,13 +180,13 @@ func benchmarkStream(t *testing.B, crypto CryptoMethod) {
 		go func() {
 			defer ac.Close()
 			defer wg.Done()
-			rw, err := InitiateHandshake(ac, []byte("cats"), ia, crypto)
+			rw, _, err := InitiateHandshake(ac, []byte("cats"), ia, crypto)
 			require.NoError(t, err)
 			require.NoError(t, readAndWrite(rw, ar, a))
 		}()
 		func() {
 			defer bc.Close()
-			rw, err := ReceiveHandshake(bc, sliceIter([][]byte{[]byte("cats")}), func(CryptoMethod) CryptoMethod { return crypto })
+			rw, _, err := ReceiveHandshake(bc, sliceIter([][]byte{[]byte("cats")}), func(CryptoMethod) CryptoMethod { return crypto })
 			require.NoError(t, err)
 			require.NoError(t, readAndWrite(rw, br, b))
 		}()