perf(cmpp): process inbound submits within client window

gateway/internal/inbound/sessions.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"time"
 )
 
@@ -30,6 +31,8 @@ type downstreamSession struct {
 	applicationID  string
 	enterpriseCode string
 	protocol       string
+	windowSize     int
+	submitInFlight *atomic.Int64
 	srcID          string
 	phoneNumber    string
 	gatewayMsgID   uint64
@@ -123,6 +126,39 @@ func findSessionByConn(conn *cmpp.Conn) *downstreamSession {
 	return downstreamRegistry.byConn[conn]
 }
 
+func submitWindowByConn(conn *cmpp.Conn) int {
+	session := findSessionByConn(conn)
+	if session == nil || session.windowSize < 1 {
+		return 1
+	}
+	return session.windowSize
+}
+
+func beginInboundSubmit(session *downstreamSession) func() {
+	if session == nil || session.submitInFlight == nil {
+		return func() {}
+	}
+	session.submitInFlight.Add(1)
+	return func() { session.submitInFlight.Add(-1) }
+}
+
+func SubmitSlotSnapshot() (int, int64) {
+	downstreamRegistry.RLock()
+	defer downstreamRegistry.RUnlock()
+	configured := 0
+	var inFlight int64
+	for _, session := range downstreamRegistry.byConn {
+		if session == nil {
+			continue
+		}
+		configured += max(1, session.windowSize)
+		if session.submitInFlight != nil {
+			inFlight += session.submitInFlight.Load()
+		}
+	}
+	return configured, inFlight
+}
+
 func rememberDownstream(session downstreamSession) {
 	if session.messageID == "" || session.conn == nil {
 		return