distribution/storage/blobstore.go

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package storage
import (
"fmt"
"github.com/Sirupsen/logrus"
"github.com/docker/distribution/digest"
"github.com/docker/distribution/storagedriver"
)
// TODO(stevvooe): Currently, the blobStore implementation used by the
// manifest store. The layer store should be refactored to better leverage the
// blobStore, reducing duplicated code.
// blobStore implements a generalized blob store over a driver, supporting the
// read side and link management. This object is intentionally a leaky
// abstraction, providing utility methods that support creating and traversing
// backend links.
type blobStore struct {
*registry
}
// exists reports whether or not the path exists. If the driver returns error
// other than storagedriver.PathNotFound, an error may be returned.
func (bs *blobStore) exists(dgst digest.Digest) (bool, error) {
path, err := bs.path(dgst)
if err != nil {
return false, err
}
ok, err := exists(bs.driver, path)
if err != nil {
return false, err
}
return ok, nil
}
// get retrieves the blob by digest, returning it a byte slice. This should
// only be used for small objects.
func (bs *blobStore) get(dgst digest.Digest) ([]byte, error) {
bp, err := bs.path(dgst)
if err != nil {
return nil, err
}
return bs.driver.GetContent(bp)
}
// link links the path to the provided digest by writing the digest into the
// target file.
func (bs *blobStore) link(path string, dgst digest.Digest) error {
if exists, err := bs.exists(dgst); err != nil {
return err
} else if !exists {
return fmt.Errorf("cannot link non-existent blob")
}
// The contents of the "link" file are the exact string contents of the
// digest, which is specified in that package.
return bs.driver.PutContent(path, []byte(dgst))
}
// linked reads the link at path and returns the content.
func (bs *blobStore) linked(path string) ([]byte, error) {
linked, err := bs.readlink(path)
if err != nil {
return nil, err
}
return bs.get(linked)
}
// readlink returns the linked digest at path.
func (bs *blobStore) readlink(path string) (digest.Digest, error) {
content, err := bs.driver.GetContent(path)
if err != nil {
return "", err
}
linked, err := digest.ParseDigest(string(content))
if err != nil {
return "", err
}
if exists, err := bs.exists(linked); err != nil {
return "", err
} else if !exists {
return "", fmt.Errorf("link %q invalid: blob %s does not exist", path, linked)
}
return linked, nil
}
// resolve reads the digest link at path and returns the blob store link.
func (bs *blobStore) resolve(path string) (string, error) {
dgst, err := bs.readlink(path)
if err != nil {
return "", err
}
return bs.path(dgst)
}
// 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.
func (bs *blobStore) put(p []byte) (digest.Digest, error) {
dgst, err := digest.FromBytes(p)
if err != nil {
logrus.Errorf("error digesting content: %v, %s", err, string(p))
return "", err
}
bp, err := bs.path(dgst)
if err != nil {
return "", err
}
// If the content already exists, just return the digest.
if exists, err := bs.exists(dgst); err != nil {
return "", err
} else if exists {
return dgst, nil
}
return dgst, bs.driver.PutContent(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
}
// exists provides a utility method to test whether or not
func exists(driver storagedriver.StorageDriver, path string) (bool, error) {
if _, err := driver.Stat(path); err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
return false, nil
default:
return false, err
}
}
return true, nil
}