Make both initiator and acceptor fixIn channels buffered

acceptor.go

@@ -359,7 +359,7 @@ func (a *Acceptor) handleConnection(netConn net.Conn) {
 	}
 
 	a.sessionAddr.Store(sessID, netConn.RemoteAddr())
-	msgIn := make(chan fixIn)
+	msgIn := make(chan fixIn, session.InChanCapacity)
 	msgOut := make(chan []byte)
 
 	if err := session.connect(msgIn, msgOut); err != nil {

config/configuration.go

@@ -489,6 +489,16 @@ const (
 	// Valid Values:
 	//  - Any positive integer
 	MaxLatency string = "MaxLatency"
+
+	// InChanCapacity sets the maximum number of messages that can be buffered in the channel for incoming FIX messages.
+	//
+	// Required: No
+	//
+	// Default: 1
+	//
+	// Valid Values:
+	//  - A positive integer, or zero for an unbuffered channel
+	InChanCapacity string = "InChanCapacity"
 )
 
 const (

initiator.go

@@ -205,7 +205,7 @@ func (i *Initiator) handleConnection(session *session, tlsConfig *tls.Config, di
 			netConn = tlsConn
 		}
 
-		msgIn = make(chan fixIn)
+		msgIn = make(chan fixIn, session.InChanCapacity)
 		msgOut = make(chan []byte)
 		if err := session.connect(msgIn, msgOut); err != nil {
 			session.log.OnEventf("Failed to initiate: %v", err)

internal/session_settings.go

@@ -21,6 +21,7 @@ type SessionSettings struct {
 	TimeZone                     *time.Location
 	ResetSeqTime                 time.Time
 	EnableResetSeqTime           bool
+	InChanCapacity               int
 
 	// Required on logon for FIX.T.1 messages.
 	DefaultApplVerID string

session.go

@@ -757,6 +757,21 @@ func (s *session) checkBeginString(msg *Message) MessageRejectError {
 	return nil
 }
 
+func (s *session) drainMessageIn() {
+	s.log.OnEventf("Draining %d messages from inbound channel...", len(s.messageIn))
+	for {
+		select {
+		case fixInc, ok := <-s.messageIn:
+			if !ok {
+				return
+			}
+			s.Incoming(s, fixInc)
+		default:
+			return
+		}
+	}
+}
+
 func (s *session) doReject(msg *Message, rej MessageRejectError) error {
 	reply := msg.reverseRoute()
 
@@ -824,6 +839,9 @@ func (s *session) onDisconnect() {
 		s.messageOut = nil
 	}
 
+	// s.messageIn is buffered so we need to drain it before disconnection
+	s.drainMessageIn()
+
 	s.messageIn = nil
 }
 

session_factory.go

@@ -431,6 +431,18 @@ func (f sessionFactory) newSession(
 		s.DisableMessagePersist = !persistMessages
 	}
 
+	if settings.HasSetting(config.InChanCapacity) {
+		if s.InChanCapacity, err = settings.IntSetting(config.InChanCapacity); err != nil {
+			return
+		} else if s.InChanCapacity < 0 {
+			err = IncorrectFormatForSetting{Setting: config.InChanCapacity, Value: []byte(strconv.Itoa(s.InChanCapacity))}
+			return
+		}
+	} else {
+		// Default to 1 buffered message per channel
+		s.InChanCapacity = 1
+	}
+
 	if f.BuildInitiators {
 		if err = f.buildInitiatorSettings(s, settings); err != nil {
 			return