check-cutover-conn.diff

diff --git a/internal/frontend/frontend.go b/internal/frontend/frontend.go
index 3df0069..eb02d1c 100644
--- a/internal/frontend/frontend.go
+++ b/internal/frontend/frontend.go
@@ -66,6 +66,7 @@ type Frontend interface {
 	ListenForTraffic() Traffic
 	// HandleTraffic tells the frontend to handle the traffic sent.
 	HandleTraffic(ctx context.Context, traffic any) error
+	CheckIfTrafficCutover(traffic any) (bool, error)
 	PrepareResult(ctx context.Context, result Result) (any, error)
 
 	ShadowExecutor() shadow.ShadowExecutor
diff --git a/internal/proxyql/proxyql.go b/internal/proxyql/proxyql.go
index fde4b75..256e53f 100644
--- a/internal/proxyql/proxyql.go
+++ b/internal/proxyql/proxyql.go
@@ -50,7 +50,8 @@ type CutoverRequest struct {
 	// It determines the limit of wait for all connections to become tnx/query
 	// free. When the timeout is reached, abort the cutover attempt and resume
 	// the traffic.
-	BeginTimeout time.Duration
+	BeginTimeout             time.Duration
+	silentIfNoOngoingCutover bool
 }
 
 func (c *CutoverRequest) Format(b *strings.Builder) {
@@ -112,6 +113,15 @@ func HasCommandPrefix(s string) bool {
 	return i == len(compareStartWord)
 }
 
+func CheckIfStringIsCutover(s string) (bool, error) {
+	c, err := Parse(s)
+	if err != nil {
+		return false, err
+	}
+	_, ok := c.(*CutoverRequest)
+	return ok, nil
+}
+
diff --git a/internal/proxyserver/connection.go b/internal/proxyserver/connection.go
index 86b17e5..84e3527 100644
--- a/internal/proxyserver/connection.go
+++ b/internal/proxyserver/connection.go
@@ -24,6 +24,13 @@ type connection struct {
 	frontend.Frontend
 
 	key string
+	// isForCutover if the connection has issued a CONSISTENT CUTOVER BEGIN
+	// request, which trigger the traffic to pause, and all user connection and
+	// the proxy server will wait for followup request from this connection for
+	// next step. The proxy server listens to the aliveness of this connection,
+	// and once it dies, the server will inform all user connections to
+	// AUTOCOMPLETE the ongoing cutover and resume the traffic.
+	isForCutover bool
 	// trafficCh outputs 1 read packet. when traffic is read.
 	trafficCh chan frontend.Traffic
 	// readyForTrafficCh signifies that we should attempt to read another
diff --git a/internal/proxyserver/proxyserver.go b/internal/proxyserver/proxyserver.go
index 10477f8..8e03821 100644
--- a/internal/proxyserver/proxyserver.go
+++ b/internal/proxyserver/proxyserver.go
@@ -478,6 +478,9 @@ func (s *Server) handleConnection(
 	ctx context.Context, conn *connection, logger zerolog.Logger,
 ) (retErr error) {
 	defer func() {
+		if conn.isForCutover {
+			//TODO: make an artifical traffic to AUTOCOMPLETE the cutover.
+		}
 		s.conns.Delete(conn.key)
 		retErr = errors.CombineErrors(retErr, conn.Close(ctx))
 	}()
@@ -513,6 +516,11 @@ trafficLoop:
 							return errors.AssertionFailedf("unexpected followup cutover followup request")
 						}
 					case traffic, ok := <-conn.TrafficChannel():
+						isForCutover, err := conn.CheckIfTrafficCutover(traffic)
+						if err != nil {
+							return err
+						}
+						conn.isForCutover = isForCutover
 						if err := handleTraffic(ctx, conn, traffic, ok); err != nil {
 							return err
 						}
diff --git a/mysqlproxy/internal/mysqlfrontend/frontend.go b/mysqlproxy/internal/mysqlfrontend/frontend.go
index ca6728d..019c781 100644
--- a/mysqlproxy/internal/mysqlfrontend/frontend.go
+++ b/mysqlproxy/internal/mysqlfrontend/frontend.go
@@ -26,6 +26,7 @@ import (
 	"github.com/cockroachlabs/crdb-proxy/internal/frontend"
 	"github.com/cockroachlabs/crdb-proxy/internal/go-mysql/mysql"
 	mysqlserver "github.com/cockroachlabs/crdb-proxy/internal/go-mysql/server"
+	"github.com/cockroachlabs/crdb-proxy/internal/proxyql"
 	"github.com/cockroachlabs/crdb-proxy/internal/proxyqlhandler"
 	"github.com/cockroachlabs/crdb-proxy/internal/shadow"
 	"github.com/rs/zerolog"
@@ -89,6 +90,19 @@ func (f *Frontend) ListenForTraffic() frontend.Traffic {
 	return frontend.Traffic{Data: data, Err: err}
 }
 
+func (f *Frontend) CheckIfTrafficCutover(traffic any) (bool, error) {
+	trafficData := traffic.([]byte)
+	cmd := trafficData[0]
+	data := trafficData[1:]
+
+	switch cmd {
+	case mysql.COM_QUERY:
+		return proxyql.CheckIfStringIsCutover(string(data))
+	default:
+		return false, nil
+	}
+}
+
 func (f *Frontend) HandleTraffic(ctx context.Context, traffic any) error {
 	// Second half of mysql.HandleCommand - handle the packet (using the handler)
 	c := f.Conn
diff --git a/pgproxy/internal/pgfrontend/frontend.go b/pgproxy/internal/pgfrontend/frontend.go
index 765f4c2..f2eb8c9 100644
--- a/pgproxy/internal/pgfrontend/frontend.go
+++ b/pgproxy/internal/pgfrontend/frontend.go
@@ -125,6 +125,17 @@ func (f *Frontend) PrepareResult(ctx context.Context, result frontend.Result) (a
 	return nil, f.pgBackend.Flush()
 }
 
+func (f *Frontend) CheckIfTrafficCutover(traffic any) (bool, error) {
+	msg := traffic.(pgproto3.FrontendMessage)
+	switch msg := msg.(type) {
+	case *pgproto3.Query:
+		query := msg.String
+		return proxyql.CheckIfStringIsCutover(query)
+	default:
+		return false, nil
+	}
+}
+
 func (f *Frontend) HandleTraffic(ctx context.Context, traffic any) error {
 	msg := traffic.(pgproto3.FrontendMessage)