f46a1b73e8
Manifests are now fetched by a field called "reference", which may be a tag or a digest. When using digests to reference a manifest, the data is immutable. The routes and specification have been updated to allow this. There are a few caveats to this approach: 1. It may be problematic to rely on data format to differentiate between a tag and a digest. Currently, they are disjoint but there may modifications on either side that break this guarantee. 2. The caching characteristics of returned content are very different for digest versus tag-based references. Digest urls can be cached forever while tag urls cannot. Both of these are minimal caveats that we can live with in the future. Signed-off-by: Stephen J Day <stephen.day@docker.com>