define supported extensions in one place and use for both server and request-server

request-server.go

@@ -151,7 +151,7 @@ func (rs *RequestServer) packetWorker(
 		var rpkt responsePacket
 		switch pkt := pkt.requestPacket.(type) {
 		case *sshFxInitPacket:
-			rpkt = sshFxVersionPacket{Version: sftpProtocolVersion}
+			rpkt = sshFxVersionPacket{Version: sftpProtocolVersion, Extensions: sftpExtensions}
 		case *sshFxpClosePacket:
 			handle := pkt.getHandle()
 			rpkt = statusFromError(pkt, rs.closeRequest(handle))

server.go

@@ -157,11 +157,8 @@ func handlePacket(s *Server, p orderedRequest) error {
 	switch p := p.requestPacket.(type) {
 	case *sshFxInitPacket:
 		rpkt = sshFxVersionPacket{
-			Version: sftpProtocolVersion,
-			Extensions: []sshExtensionPair{
-				{"hardlink@openssh.com", "1"},
-				{"posix-rename@openssh.com", "1"},
-			},
+			Version:    sftpProtocolVersion,
+			Extensions: sftpExtensions,
 		}
 	case *sshFxpStatPacket:
 		// stat the requested file

sftp.go

@@ -85,6 +85,11 @@ const (
 	ssh_FXF_EXCL   = 0x00000020
 )
 
+var sftpExtensions = []sshExtensionPair{
+	{"hardlink@openssh.com", "1"},
+	{"posix-rename@openssh.com", "1"},
+}
+
 type fxp uint8
 
 func (f fxp) String() string {