Implement simultaneous open extension

client.go

@@ -2,8 +2,11 @@ package multistream
 
 import (
 	"bytes"
+	"crypto/rand"
+	"encoding/base64"
 	"errors"
 	"io"
+	"strings"
 )
 
 // ErrNotSupported is the error returned when the muxer does not support
@@ -14,6 +17,10 @@ var ErrNotSupported = errors.New("protocol not supported")
 // specified.
 var ErrNoProtocols = errors.New("no protocols specified")
 
+var (
+	tieBreakerPrefix = "select:"
+)
+
 // SelectProtoOrFail performs the initial multistream handshake
 // to inform the muxer of the protocol that will be used to communicate
 // on this ReadWriteCloser. It returns an error if, for example,
@@ -22,8 +29,10 @@ func SelectProtoOrFail(proto string, rwc io.ReadWriteCloser) error {
 	errCh := make(chan error, 1)
 	go func() {
 		var buf bytes.Buffer
-		delimWrite(&buf, []byte(ProtocolID))
-		delimWrite(&buf, []byte(proto))
+		if err := delitmWriteAll(&buf, []byte(ProtocolID), []byte(proto)); err != nil {
+			errCh <- err
+			return
+		}
 		_, err := io.Copy(rwc, &buf)
 		errCh <- err
 	}()
@@ -61,7 +70,80 @@ func SelectOneOf(protos []string, rwc io.ReadWriteCloser) (string, error) {
 	default:
 		return "", err
 	}
-	for _, p := range protos[1:] {
+	return selectProtosOrFail(protos[1:], rwc)
+}
+
+// Performs protocol negotiation with the simultaneous open extension; the returned boolean
+// indicator will be true if we should act as a server.
+func SelectWithSimopenOrFail(protos []string, rwc io.ReadWriteCloser) (string, bool, error) {
+	if len(protos) == 0 {
+		return "", false, ErrNoProtocols
+	}
+
+	werrCh := make(chan error, 1)
+	go func() {
+		var buf bytes.Buffer
+		if err := delitmWriteAll(&buf, []byte(ProtocolID), []byte("iamclient"), []byte(protos[0])); err != nil {
+			werrCh <- err
+			return
+		}
+
+		_, err := io.Copy(rwc, &buf)
+		werrCh <- err
+	}()
+
+	err := readMultistreamHeader(rwc)
+	if err != nil {
+		return "", false, err
+	}
+
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", false, err
+	}
+
+	if err = <-werrCh; 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":
+		return selectProtosOrFail(protos[1:], rwc)
+	default:
+		return "", errors.New("unexpected response: " + tok)
+	}
+}
+
+func selectProtosOrFail(protos []string, rwc io.ReadWriteCloser) (string, error) {
+	for _, p := range protos {
 		err := trySelect(p, rwc)
 		switch err {
 		case nil:
@@ -74,6 +156,141 @@ func SelectOneOf(protos []string, rwc io.ReadWriteCloser) (string, error) {
 	return "", ErrNotSupported
 }
 
+func simOpen(protos []string, rwc io.ReadWriteCloser) (string, bool, error) {
+	mynonce := make([]byte, 32)
+	_, err := rand.Read(mynonce)
+	if err != nil {
+		return "", false, err
+	}
+
+	werrCh := make(chan error, 1)
+	go func() {
+		myselect := []byte(tieBreakerPrefix + base64.StdEncoding.EncodeToString(mynonce))
+		err := delimWriteBuffered(rwc, myselect)
+		werrCh <- err
+	}()
+
+	// skip exactly one protocol
+	// see https://github.com/multiformats/go-multistream/pull/42#discussion_r558757135
+	_, err = ReadNextToken(rwc)
+	if err != nil {
+		return "", false, err
+	}
+
+	// read the tie breaker nonce
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", false, err
+	}
+	if !strings.HasPrefix(tok, tieBreakerPrefix) {
+		return "", false, errors.New("tie breaker nonce not sent with the correct prefix")
+	}
+
+	if err = <-werrCh; err != nil {
+		return "", false, err
+	}
+
+	peernonce, err := base64.StdEncoding.DecodeString(tok[7:])
+	if err != nil {
+		return "", false, err
+	}
+
+	var iamserver bool
+	switch bytes.Compare(mynonce, peernonce) {
+	case -1:
+		// peer nonce bigger, he is client
+		iamserver = true
+
+	case 1:
+		// my nonce bigger, i am client
+		iamserver = false
+
+	case 0:
+		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) {
+	werrCh := make(chan error, 1)
+	go func() {
+		err := delimWriteBuffered(rwc, []byte("responder"))
+		werrCh <- err
+	}()
+
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", err
+	}
+	if tok != "initiator" {
+		return "", errors.New("unexpected response: " + tok)
+	}
+	if err = <-werrCh; err != nil {
+		return "", err
+	}
+
+	for {
+		tok, err = ReadNextToken(rwc)
+
+		if err == io.EOF {
+			return "", ErrNotSupported
+		}
+
+		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) {
+	werrCh := make(chan error, 1)
+	go func() {
+		err := delimWriteBuffered(rwc, []byte("initiator"))
+		werrCh <- err
+	}()
+
+	tok, err := ReadNextToken(rwc)
+	if err != nil {
+		return "", err
+	}
+	if tok != "responder" {
+		return "", errors.New("unexpected response: " + tok)
+	}
+	if err = <-werrCh; err != nil {
+		return "", err
+	}
+
+	return selectProtosOrFail(protos, rwc)
+}
+
 func handshake(rw io.ReadWriter) error {
 	errCh := make(chan error, 1)
 	go func() {

multistream.go

@@ -7,6 +7,7 @@ import (
 	"bufio"
 	"bytes"
 	"errors"
+	"fmt"
 
 	"io"
 	"sync"
@@ -81,6 +82,16 @@ func delimWriteBuffered(w io.Writer, mes []byte) error {
 	return bw.Flush()
 }
 
+func delitmWriteAll(w io.Writer, messages ...[]byte) error {
+	for _, mes := range messages {
+		if err := delimWrite(w, mes); err != nil {
+			return fmt.Errorf("failed to write messages %s, err: %v	", string(mes), err)
+		}
+	}
+
+	return nil
+}
+
 func delimWrite(w io.Writer, mes []byte) error {
 	err := writeUvarint(w, uint64(len(mes)+1))
 	if err != nil {