Han's uniform in TFA (spoiler)

[J.T.B.]

I think Han's history as some kind of Imperial officer was described in Brian Daley's Han Solo trilogy.

No. An incident from his time as a "cadet" was described but it sounded more like the Academy Luke wanted to attend, which was originally not Imperial but was apparently later retconned to be so. Solo was also described as being stripped of his officer insignia after being framed, but it wasn't said he was an Imperial officer and indeed they don't wear the trouser stripes which he was said to have retained from his earlier uniform.

Whatever those cylinders in Han's jacket are supposed to be, they look a little too big to be rank code cylinders and those things I think tend to have little clips on the end, like the kind you get on a pen.

Costumes in Star Wars tend to have all sorts of mysterious devices and accessories without any specific purpose in mind, so I wouldn't read too much into it. They could be spare ammo, power cells, small tools, signal flares, just about anything really.

Yeah. The rebel pilots always had silver cylinder things in their flight suit sleeve pockets, too, of a different design from the Imperial ones, which were really radiation dosimeters.