get file via tftp and write to filesystem, get length of tftp transfer

Hello, is it possible to download a file via network (tftp) and write it to a filesystem as ext4? This looks like a combination of tftpboot and ext4write but how to get sizebytes? I don't find how to get the length information from tftpboot into a variable - it seems to me only displayed on screen. Did I miss something? Thanks for you patience. Elmar