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spec: fetch manifests by tag or digest

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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>
This commit is contained in:
Stephen J Day 2015-02-25 18:04:28 -08:00
parent 0ecb468a33
commit f46a1b73e8
4 changed files with 48 additions and 15 deletions
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7
docs/api/v2/urls.go
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@ -107,11 +107,12 @@ func (ub *URLBuilder) BuildTagsURL(name string) (string, error) {
return tagsURL.String(), nil
}
// BuildManifestURL constructs a url for the manifest identified by name and tag.
func (ub *URLBuilder) BuildManifestURL(name, tag string) (string, error) {
// BuildManifestURL constructs a url for the manifest identified by name and
// reference. The argument reference may be either a tag or digest.
func (ub *URLBuilder) BuildManifestURL(name, reference string) (string, error) {
route := ub.cloneRoute(RouteNameManifest)
manifestURL, err := route.URL("name", name, "tag", tag)
manifestURL, err := route.URL("name", name, "reference", reference)
if err != nil {
return "", err
}