distribution errors. Fill in missing checks for mutations on a registry pull-through
cache. Add unit tests and update documentation.
Also, give v2.ErrorCodeUnsupported an HTTP status code, previously it was
defaulting to 500, now its 405 Method Not Allowed.
Signed-off-by: Richard Scothern <richard.scothern@gmail.com>
Several error codes are generally useful but tied to the v2 specification
definitions. This change moves these error code definitions into the common
package for use by the health package, which is not tied to the v2 API.
Signed-off-by: Stephen J Day <stephen.day@docker.com>