Good point. Initially I thought about either just a typealias:

type Range = (u64, u64)

or maybe better a tuple struct:

struct Range(u64, u64)

But builtin Range should do the job. It shouldn't be any more expensive from a tuple, memory footprint should be the same as this is a two-integer struct.

The only problem with the built-in one is that in docs, end is marked as exclusive, but in fact S3 expects HTTP Range header format, which has inclusive end. Eventually, we could just subtract 1 from the value of end.

It looks like the start..=end expression produces a std::ops::RangeInclusive instance, which is another built-in struct for ranges.
So this is another solution to go, maybe the best as we can use the ..= expression which tells us that the range is inclusive.
Or we could be even more general and just require a std::ops::RangeBounds trait which accepts all ranges, including unbound ones.

Using RangeBounds sounds like a great idea! Just one concern is if we can support unbounded ranges. Can we specify an open ended HTTP Range?