Use common packet typing code

Remove duplication due to request code being separate.

server.go

@@ -124,61 +124,14 @@ type rxPacket struct {
 // Up to N parallel servers
 func (svr *Server) sftpServerWorker() error {
 	for p := range svr.pktChan {
-		var pkt interface {
-			encoding.BinaryUnmarshaler
-			id() uint32
-		}
-		var readonly = true
-		switch p.pktType {
-		case ssh_FXP_INIT:
-			pkt = &sshFxInitPacket{}
-		case ssh_FXP_LSTAT:
-			pkt = &sshFxpLstatPacket{}
-		case ssh_FXP_OPEN:
-			pkt = &sshFxpOpenPacket{}
-			// readonly handled specially below
-		case ssh_FXP_CLOSE:
-			pkt = &sshFxpClosePacket{}
-		case ssh_FXP_READ:
-			pkt = &sshFxpReadPacket{}
-		case ssh_FXP_WRITE:
-			pkt = &sshFxpWritePacket{}
-		case ssh_FXP_FSTAT:
-			pkt = &sshFxpFstatPacket{}
-		case ssh_FXP_SETSTAT:
-			pkt = &sshFxpSetstatPacket{}
-		case ssh_FXP_FSETSTAT:
-			pkt = &sshFxpFsetstatPacket{}
-		case ssh_FXP_OPENDIR:
-			pkt = &sshFxpOpendirPacket{}
-		case ssh_FXP_READDIR:
-			pkt = &sshFxpReaddirPacket{}
-		case ssh_FXP_REMOVE:
-			pkt = &sshFxpRemovePacket{}
-		case ssh_FXP_MKDIR:
-			pkt = &sshFxpMkdirPacket{}
-		case ssh_FXP_RMDIR:
-			pkt = &sshFxpRmdirPacket{}
-		case ssh_FXP_REALPATH:
-			pkt = &sshFxpRealpathPacket{}
-		case ssh_FXP_STAT:
-			pkt = &sshFxpStatPacket{}
-		case ssh_FXP_RENAME:
-			pkt = &sshFxpRenamePacket{}
-		case ssh_FXP_READLINK:
-			pkt = &sshFxpReadlinkPacket{}
-		case ssh_FXP_SYMLINK:
-			pkt = &sshFxpSymlinkPacket{}
-		case ssh_FXP_EXTENDED:
-			pkt = &sshFxpExtendedPacket{}
-		default:
-			return errors.Errorf("unhandled packet type: %s", p.pktType)
-		}
-		if err := pkt.UnmarshalBinary(p.pktBytes); err != nil {
+
+		pkt, err := makePacket(p)
+		if err != nil {
 			return err
 		}
 
 		// readonly checks
+		readonly := true
 		switch pkt := pkt.(type) {
 		case notReadOnly:
 			readonly = false