distribution/docs/storage/blobstore.go

package storage

import (
	"github.com/docker/distribution"
	"github.com/docker/distribution/context"
	"github.com/docker/distribution/digest"
	"github.com/docker/distribution/registry/storage/driver"
)

// blobStore implements a the read side of the blob store interface over a
// driver without enforcing per-repository membership. This object is
// intentionally a leaky abstraction, providing utility methods that support
// creating and traversing backend links.
type blobStore struct {
	driver  driver.StorageDriver
	pm      *pathMapper
	statter distribution.BlobStatter
}

var _ distribution.BlobProvider = &blobStore{}

// Get implements the BlobReadService.Get call.
func (bs *blobStore) Get(ctx context.Context, dgst digest.Digest) ([]byte, error) {
	bp, err := bs.path(dgst)
	if err != nil {
		return nil, err
	}

	p, err := bs.driver.GetContent(ctx, bp)
	if err != nil {
		switch err.(type) {
		case driver.PathNotFoundError:
			return nil, distribution.ErrBlobUnknown
		}

		return nil, err
	}

	return p, err
}

func (bs *blobStore) Open(ctx context.Context, dgst digest.Digest) (distribution.ReadSeekCloser, error) {
	desc, err := bs.statter.Stat(ctx, dgst)
	if err != nil {
		return nil, err
	}

	path, err := bs.path(desc.Digest)
	if err != nil {
		return nil, err
	}

	return newFileReader(ctx, bs.driver, path, desc.Size)
}

// Put stores the content p in the blob store, calculating the digest. If the
// content is already present, only the digest will be returned. This should
// only be used for small objects, such as manifests. This implemented as a convenience for other Put implementations
func (bs *blobStore) Put(ctx context.Context, mediaType string, p []byte) (distribution.Descriptor, error) {
	dgst, err := digest.FromBytes(p)
	if err != nil {
		context.GetLogger(ctx).Errorf("blobStore: error digesting content: %v, %s", err, string(p))
		return distribution.Descriptor{}, err
	}

	desc, err := bs.statter.Stat(ctx, dgst)
	if err == nil {
		// content already present
		return desc, nil
	} else if err != distribution.ErrBlobUnknown {
		context.GetLogger(ctx).Errorf("blobStore: error stating content (%v): %#v", dgst, err)
		// real error, return it
		return distribution.Descriptor{}, err
	}

	bp, err := bs.path(dgst)
	if err != nil {
		return distribution.Descriptor{}, err
	}

	// TODO(stevvooe): Write out mediatype here, as well.

	return distribution.Descriptor{
		Size: int64(len(p)),

		// NOTE(stevvooe): The central blob store firewalls media types from
		// other users. The caller should look this up and override the value
		// for the specific repository.
		MediaType: "application/octet-stream",
		Digest:    dgst,
	}, bs.driver.PutContent(ctx, bp, p)
}

// path returns the canonical path for the blob identified by digest. The blob
// may or may not exist.
func (bs *blobStore) path(dgst digest.Digest) (string, error) {
	bp, err := bs.pm.path(blobDataPathSpec{
		digest: dgst,
	})

	if err != nil {
		return "", err
	}

	return bp, nil
}

// link links the path to the provided digest by writing the digest into the
// target file. Caller must ensure that the blob actually exists.
func (bs *blobStore) link(ctx context.Context, path string, dgst digest.Digest) error {
	// The contents of the "link" file are the exact string contents of the
	// digest, which is specified in that package.
	return bs.driver.PutContent(ctx, path, []byte(dgst))
}

// readlink returns the linked digest at path.
func (bs *blobStore) readlink(ctx context.Context, path string) (digest.Digest, error) {
	content, err := bs.driver.GetContent(ctx, path)
	if err != nil {
		return "", err
	}

	linked, err := digest.ParseDigest(string(content))
	if err != nil {
		return "", err
	}

	return linked, nil
}

// resolve reads the digest link at path and returns the blob store path.
func (bs *blobStore) resolve(ctx context.Context, path string) (string, error) {
	dgst, err := bs.readlink(ctx, path)
	if err != nil {
		return "", err
	}

	return bs.path(dgst)
}

type blobStatter struct {
	driver driver.StorageDriver
	pm     *pathMapper
}

var _ distribution.BlobStatter = &blobStatter{}

// Stat implements BlobStatter.Stat by returning the descriptor for the blob
// in the main blob store. If this method returns successfully, there is
// strong guarantee that the blob exists and is available.
func (bs *blobStatter) Stat(ctx context.Context, dgst digest.Digest) (distribution.Descriptor, error) {
	path, err := bs.pm.path(blobDataPathSpec{
		digest: dgst,
	})
	if err != nil {
		return distribution.Descriptor{}, err
	}

	fi, err := bs.driver.Stat(ctx, path)
	if err != nil {
		switch err := err.(type) {
		case driver.PathNotFoundError:
			return distribution.Descriptor{}, distribution.ErrBlobUnknown
		default:
			return distribution.Descriptor{}, err
		}
	}

	if fi.IsDir() {
		// NOTE(stevvooe): This represents a corruption situation. Somehow, we
		// calculated a blob path and then detected a directory. We log the
		// error and then error on the side of not knowing about the blob.
		context.GetLogger(ctx).Warnf("blob path should not be a directory: %q", path)
		return distribution.Descriptor{}, distribution.ErrBlobUnknown
	}

	// TODO(stevvooe): Add method to resolve the mediatype. We can store and
	// cache a "global" media type for the blob, even if a specific repo has a
	// mediatype that overrides the main one.

	return distribution.Descriptor{
		Size: fi.Size(),

		// NOTE(stevvooe): The central blob store firewalls media types from
		// other users. The caller should look this up and override the value
		// for the specific repository.
		MediaType: "application/octet-stream",
		Digest:    dgst,
	}, nil
}