[steveklabnik]

> Is it possible for me to use the pieces described above without explicitly listing these crates?

Not unless iron exposed them directly. I haven't used it a while, so I'm not sure if it does.

> If not, why do I need to declare hyper as a dependency when iron is already using it?

There's a difference between a direct and transitive dependency, it's not going to just inherently bring transitive stuff into scope.

> Perhaps I don't need to, and I was just unable to figure out how to get the `header!` macro from iron directly.

Yeah I haven't used iron in long enough to say, but this is theoretically possible.

> My initial expectation was that iron would either wrap or expose every part of hyper that I might need.

Yes, it is possible that iron's API isn't the best here.