use a dedicated error code when a connection is gated

0x47415445 is GATE in ASCII.

p2p/transport/quic/listener.go

@@ -3,7 +3,6 @@ package libp2pquic
 import (
 	"context"
 	"crypto/tls"
-	"fmt"
 	"net"
 
 	ic "github.com/libp2p/go-libp2p-core/crypto"
@@ -69,11 +68,15 @@ func (l *listener) Accept() (tpt.CapableConn, error) {
 			sess.CloseWithError(0, err.Error())
 			continue
 		}
+		if l.transport.gater != nil && !l.transport.gater.InterceptSecured(n.DirInbound, conn.remotePeerID, conn) {
+			sess.CloseWithError(errorCodeConnectionGating, "connection gated")
+			continue
+		}
 		return conn, nil
 	}
 }
 
-func (l *listener) setupConn(sess quic.Session) (tpt.CapableConn, error) {
+func (l *listener) setupConn(sess quic.Session) (*conn, error) {
 	// The tls.Config used to establish this connection already verified the certificate chain.
 	// Since we don't have any way of knowing which tls.Config was used though,
 	// we have to re-determine the peer's identity here.
@@ -92,11 +95,6 @@ func (l *listener) setupConn(sess quic.Session) (tpt.CapableConn, error) {
 		return nil, err
 	}
 
-	connaddrs := &connAddrs{lmAddr: l.localMultiaddr, rmAddr: remoteMultiaddr}
-	if l.transport.gater != nil && !l.transport.gater.InterceptSecured(n.DirInbound, remotePeerID, connaddrs) {
-		return nil, fmt.Errorf("secured connection gated")
-	}
-
 	return &conn{
 		sess:            sess,
 		transport:       l.transport,

p2p/transport/quic/transport.go

@@ -40,6 +40,7 @@ var quicConfig = &quic.Config{
 }
 
 const statelessResetKeyInfo = "libp2p quic stateless reset key"
+const errorCodeConnectionGating = 0x47415445 // GATE in ASCII
 
 type connManager struct {
 	reuseUDP4 *reuse
@@ -184,7 +185,7 @@ func (t *transport) Dial(ctx context.Context, raddr ma.Multiaddr, p peer.ID) (tp
 
 	connaddrs := &connAddrs{lmAddr: localMultiaddr, rmAddr: remoteMultiaddr}
 	if t.gater != nil && !t.gater.InterceptSecured(n.DirOutbound, p, connaddrs) {
-		sess.CloseWithError(0, "")
+		sess.CloseWithError(errorCodeConnectionGating, "connection gated")
 		return nil, fmt.Errorf("secured connection gated")
 	}