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images, remotes: add support for foreign layers

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Add support for downloading layers with external URLs and
foreign/non-distributable mediatypes. This ensures that encountered
windows images are downloaded correctly. We still need to filter out the
extra windows resources when pulling linux, but this is a step towards
correctly supporting multi-platform images.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
This commit is contained in:
Stephen J Day
2017-09-20 17:06:13 -07:00
parent 9934acb271
commit 13771fba83
4 changed files with 28 additions and 14 deletions
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25
remotes/docker/fetcher.go
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@@ -7,6 +7,7 @@ import (
"path"
"strings"
"github.com/containerd/containerd/errdefs"
"github.com/containerd/containerd/images"
"github.com/containerd/containerd/log"
ocispec "github.com/opencontainers/image-spec/specs-go/v1"
@@ -26,7 +27,7 @@ func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.R
},
))
paths, err := getV2URLPaths(desc)
urls, err := r.getV2URLPaths(ctx, desc)
if err != nil {
return nil, err
}
@@ -36,9 +37,7 @@ func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.R
return nil, err
}
for _, path := range paths {
u := r.url(path)
for _, u := range urls {
req, err := http.NewRequest(http.MethodGet, u, nil)
if err != nil {
return nil, err
@@ -61,24 +60,34 @@ func (r dockerFetcher) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.R
return resp.Body, nil
}
return nil, errors.New("not found")
return nil, errors.Wrapf(errdefs.ErrNotFound,
"could not fetch content descriptor %v (%v) from remote",
desc.Digest, desc.MediaType)
}
// getV2URLPaths generates the candidate urls paths for the object based on the
// set of hints and the provided object id. URLs are returned in the order of
// most to least likely succeed.
func getV2URLPaths(desc ocispec.Descriptor) ([]string, error) {
func (r *dockerFetcher) getV2URLPaths(ctx context.Context, desc ocispec.Descriptor) ([]string, error) {
var urls []string
if len(desc.URLs) > 0 {
// handle fetch via external urls.
for _, u := range desc.URLs {
log.G(ctx).WithField("url", u).Debug("adding alternative url")
urls = append(urls, u)
}
}
switch desc.MediaType {
case images.MediaTypeDockerSchema2Manifest, images.MediaTypeDockerSchema2ManifestList,
images.MediaTypeDockerSchema1Manifest,
ocispec.MediaTypeImageManifest, ocispec.MediaTypeImageIndex:
urls = append(urls, path.Join("manifests", desc.Digest.String()))
urls = append(urls, r.url(path.Join("manifests", desc.Digest.String())))
}
// always fallback to attempting to get the object out of the blobs store.
urls = append(urls, path.Join("blobs", desc.Digest.String()))
urls = append(urls, r.url(path.Join("blobs", desc.Digest.String())))
return urls, nil
}