Bug: For Logon/Logout/Resend/SequenceReset messages we should wait until sent (#21)

## Issue 
When log on request was queued because cannot be send due to connection
not ready,
Then it goes through the [main session
loop](https://github.com/alpacahq/quickfix/blob/5dcde41f3e6e68e93e1fd381761cd9c7843aec43/session.go#L821-L841)
which leads to
[SendAppMessages](https://github.com/alpacahq/quickfix/blob/5dcde41f3e6e68e93e1fd381761cd9c7843aec43/session_state.go#L107-L111)

But, since session is not logged on yet because the message queued is
the log on message, we drop the `toSend` queued messages so we lose the
log on message itself.


## Proposed solution
For important messages like Logon/Logout/Resend/SequenceReset we block
until sent.

Author: AlexandrosKyriakakis

logon_state_test.go

@@ -333,7 +333,7 @@ func (s *LogonStateTestSuite) TestFixMsgInLogonSeqNumTooHigh() {
 	s.Require().Nil(err)
 	s.MessageType(string(msgTypeLogon), sentMessage)
 
-	s.session.sendQueued()
+	s.session.sendQueued(true)
 	s.MessageType(string(msgTypeResendRequest), s.MockApp.lastToAdmin)
 	s.FieldEquals(tagBeginSeqNo, 1, s.MockApp.lastToAdmin.Body)
 
@@ -373,7 +373,7 @@ func (s *LogonStateTestSuite) TestFixMsgInLogonSeqNumTooLow() {
 	s.Require().Nil(err)
 	s.MessageType(string(msgTypeLogout), sentMessage)
 
-	s.session.sendQueued()
+	s.session.sendQueued(true)
 	s.MessageType(string(msgTypeLogout), s.MockApp.lastToAdmin)
 	s.FieldEquals(tagText, "MsgSeqNum too low, expecting 2 but received 1", s.MockApp.lastToAdmin.Body)
 }

session.go

@@ -265,7 +265,7 @@ func (s *session) sendInReplyTo(msg *Message, inReplyTo *Message) error {
 	}
 
 	s.toSend = append(s.toSend, msgBytes)
-	s.sendQueued()
+	s.sendQueued(true)
 
 	return nil
 }
@@ -294,7 +294,7 @@ func (s *session) dropAndSendInReplyTo(msg *Message, inReplyTo *Message) error {
 
 	s.dropQueued()
 	s.toSend = append(s.toSend, msgBytes)
-	s.sendQueued()
+	s.sendQueued(true)
 
 	return nil
 }
@@ -350,9 +350,9 @@ func (s *session) persist(seqNum int, msgBytes []byte) error {
 	return s.store.IncrNextSenderMsgSeqNum()
 }
 
-func (s *session) sendQueued() {
+func (s *session) sendQueued(blockUntilSent bool) {
 	for i, msgBytes := range s.toSend {
-		if !s.sendBytes(msgBytes) {
+		if !s.sendBytes(msgBytes, blockUntilSent) {
 			s.toSend = s.toSend[i:]
 			s.notifyMessageOut()
 			return
@@ -371,15 +371,22 @@ func (s *session) EnqueueBytesAndSend(msg []byte) {
 	defer s.sendMutex.Unlock()
 
 	s.toSend = append(s.toSend, msg)
-	s.sendQueued()
+	s.sendQueued(true)
 }
 
-func (s *session) sendBytes(msg []byte) bool {
+func (s *session) sendBytes(msg []byte, blockUntilSent bool) bool {
 	if s.messageOut == nil {
 		s.log.OnEventf("Failed to send: disconnected")
 		return false
 	}
 
+	if blockUntilSent {
+		s.messageOut <- msg
+		s.log.OnOutgoing(msg)
+		s.stateTimer.Reset(s.HeartBtInt)
+		return true
+	}
+
 	select {
 	case s.messageOut <- msg:
 		s.log.OnOutgoing(msg)

session_state.go

@@ -105,7 +105,7 @@ func (sm *stateMachine) SendAppMessages(session *session) {
 	defer session.sendMutex.Unlock()
 
 	if session.IsLoggedOn() {
-		session.sendQueued()
+		session.sendQueued(false)
 	} else {
 		session.dropQueued()
 	}