implement simultaneous open extension

client.go

@@ -2,8 +2,11 @@ package multistream
 
 import (
 	"bytes"
+	"crypto/rand"
 	"errors"
 	"io"
+	"math/big"
+	"strings"
 )
 
 // ErrNotSupported is the error returned when the muxer does not support
@@ -74,6 +77,218 @@ func SelectOneOf(protos []string, rwc io.ReadWriteCloser) (string, error) {
 	return "", ErrNotSupported
 }
 
+// Performs protocol negotiation with the simultaneous open extension; the returned boolean
+// indicator will be true if we should act as a server.
+func SelectWithSimopen(protos []string, rwc io.ReadWriteCloser) (string, bool, error) {
+	if len(protos) == 0 {
+		return "", false, ErrNoProtocols
+	}
+
+	var buf bytes.Buffer
+	delimWrite(&buf, []byte(ProtocolID))
+	delimWrite(&buf, []byte("iamclient"))
+	delimWrite(&buf, []byte(protos[0]))
+	_, err := io.Copy(rwc, &buf)
+	if err != nil {
+		return "", false, err
+	}
+
+	err = readMultistreamHeader(rwc)
+	if err != nil {
+		return "", false, err
+	}
+
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", false, err
+	}
+
+	switch tok {
+	case "iamclient":
+		// simultaneous open
+		return simOpen(protos, rwc)
+
+	case "na":
+		// client open
+		proto, err := clientOpen(protos, rwc)
+		if err != nil {
+			return "", false, err
+		}
+
+		return proto, false, nil
+
+	default:
+		return "", false, errors.New("unexpected response: " + tok)
+	}
+}
+
+func clientOpen(protos []string, rwc io.ReadWriteCloser) (string, error) {
+	// check to see if we selected the pipelined protocol
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", err
+	}
+
+	switch tok {
+	case protos[0]:
+		return tok, nil
+	case "na":
+		// try the other protos
+		for _, p := range protos[1:] {
+			err = trySelect(p, rwc)
+			switch err {
+			case nil:
+				return p, nil
+			case ErrNotSupported:
+			default:
+				return "", err
+			}
+		}
+
+		return "", ErrNotSupported
+	default:
+		return "", errors.New("unexpected response: " + tok)
+	}
+}
+
+func simOpen(protos []string, rwc io.ReadWriteCloser) (string, bool, error) {
+	retries := 3
+
+again:
+	mynonce := make([]byte, 32)
+	_, err := rand.Read(mynonce)
+	if err != nil {
+		return "", false, err
+	}
+
+	myselect := []byte("select:" + string(mynonce))
+	err = delimWriteBuffered(rwc, myselect)
+	if err != nil {
+		return "", false, err
+	}
+
+	var peerselect string
+	for {
+		tok, err := ReadNextToken(rwc)
+		if err != nil {
+			return "", false, err
+		}
+
+		// this skips pipelined protocol negoatiation
+		// keep reading until the token starts with select:
+		if strings.HasPrefix(tok, "select:") {
+			peerselect = tok
+			break
+		}
+	}
+
+	peernonce := []byte(peerselect[7:])
+
+	var mybig, peerbig big.Int
+	var iamserver bool
+	mybig.SetBytes(mynonce)
+	peerbig.SetBytes(peernonce)
+
+	switch mybig.Cmp(&peerbig) {
+	case -1:
+		// peer nonce bigger, he is client
+		iamserver = true
+
+	case 1:
+		// my nonce bigger, i am client
+		iamserver = false
+
+	case 0:
+		// wtf, the world is ending! try again.
+		if retries > 0 {
+			retries--
+			goto again
+		}
+
+		return "", false, errors.New("failed client selection; identical nonces!")
+
+	default:
+		return "", false, errors.New("wut? bigint.Cmp returned unexpected value")
+	}
+
+	var proto string
+	if iamserver {
+		proto, err = simOpenSelectServer(protos, rwc)
+	} else {
+		proto, err = simOpenSelectClient(protos, rwc)
+	}
+
+	return proto, iamserver, err
+}
+
+func simOpenSelectServer(protos []string, rwc io.ReadWriteCloser) (string, error) {
+	err := delimWriteBuffered(rwc, []byte("responder"))
+	if err != nil {
+		return "", err
+	}
+
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", err
+	}
+	if tok != "initiator" {
+		return "", errors.New("unexpected response: " + tok)
+	}
+
+	for {
+		tok, err = ReadNextToken(rwc)
+		if err != nil {
+			return "", err
+		}
+
+		for _, p := range protos {
+			if tok == p {
+				err = delimWriteBuffered(rwc, []byte(p))
+				if err != nil {
+					return "", err
+				}
+
+				return p, nil
+			}
+		}
+
+		err = delimWriteBuffered(rwc, []byte("na"))
+		if err != nil {
+			return "", err
+		}
+	}
+
+}
+
+func simOpenSelectClient(protos []string, rwc io.ReadWriteCloser) (string, error) {
+	err := delimWriteBuffered(rwc, []byte("initiator"))
+	if err != nil {
+		return "", err
+	}
+
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", err
+	}
+	if tok != "responder" {
+		return "", errors.New("unexpected response: " + tok)
+	}
+
+	for _, p := range protos {
+		err = trySelect(p, rwc)
+		switch err {
+		case nil:
+			return p, nil
+
+		case ErrNotSupported:
+		default:
+			return "", err
+		}
+	}
+
+	return "", ErrNotSupported
+}
+
 func handshake(rw io.ReadWriter) error {
 	errCh := make(chan error, 1)
 	go func() {