visa on arrival, my wife is vietnamese

Hi there,

I am french and I am living in Viet Nam for a long time, currently I have a "mien thi thuc" 5 years because I am a quarter vietnamese and my wife is vietnamese from Hanoi. I am going on holidays next week to France and get back to Vietnam on the 8th of January, I was wondering how could I get a visa, the longer the better at the arrival at the airport? thank you