I know this post is really old, but I have to reply because although BalusC's answer is marked as correct, it's not completely correct.
You have to write the query adding "[]" to foo like this:
foo[]=val1&foo[]=val2&foo[]=val3
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…