Pulp - Story #1150: As a user, I can lazily fetch repositories
As a developer I can receive headers while using download_one()
While using download_one() a developer should be able to receive the headers that were delivered with the download. These headers should be able to be given the developer as soon as nectar receives them and before any data is written to the download request.
On possible implementation would be to add the ability to register a callback which will pass the headers as arguments as soon as they are known. The developer could register this callback before initiating the download request. Another approach may be to store the headers in the download request but this needs to be done in a structured way and must be available before the data is written to the download request.