Refactor Ar::from_request() for 7% binary size reduction

main (624ff574):

    text	   data	    bss	     dec	    hex	filename
42125009	1298176	 181192	43604377	2995999	target/release/grapevine

this:

    text	   data	    bss	     dec	    hex	filename
38970001	1298920	 180768	40449689	2693699	target/release/grapevine