To be able to support multi-level repository names, the API has been adjusted
to disabiguate routes tagged image manifest routes and tag list routes. With
this effort, the regular expressions have been defined in a single place to
reduce repitition and ensure that validation is consistent across the registry.
The router was also refactored to remove the use of subrouters, simplifying the
route definition code. This also reduces the number of regular expression match
checks during the routing process.
This changeset defines the application structure to be used for the http side
of the new registry. The main components are the App and Context structs. The
App context is instance global and manages global configuration and resources.
Context contains request-specific resources that may be created as a by-product
of an in-flight request.
To latently construct per-request handlers and leverage gorilla/mux, a dispatch
structure has been propped up next to the main handler flow. Without this, a
router and all handlers need to be constructed on every request. By
constructing handlers on each request, we ensure thread isolation and can
carefully control the security context of in-flight requests. There are unit
tests covering this functionality.
