sftp - vim save to remote server on write -

i'm trying enable sublime text sftp package saving on write vim, proving more difficult thought.

i did manage find solution save files remote server, answer incomplete. hoping 1 can elaborate me how complete task.

here example given in previous question

cmap <leader>w :nwrite ftp://user@server/path/to/file.php 

this works well, has issue if wanted work @ time file hitting ctrl+w how work without manually writing out?

does special variable exist open file?

for example

cmap <leader>w :nwrite ftp://user@server/file/path/from/project/root/$file_and_extension