Questions about extension of study permit outside Canada

[verzweifelt]

I'm currently an international student in University of Saskatchewan. Both my study permit and visa will expire at the end of July, 2017.

But I planned to travel back to China in April and return in August. In that case both of study permit and visa will expire while I'm in China. So can I apply for extension of study permit before my study permit expires in China via cic.gc.ca online, or I need to file paperwork to apply for extension to Canada Embassy in China?

Furthermore, can I still apply for renewal of my visa online via cic.gc.ca after I get new study permit but after my current visa expires in China?

I know it's kinda confusing, but can anyone help me? Thanks!