distribution/docs/storage/blobstore.go
Stephen J Day 6ab228f798 Integrate layer info cache with registry and storage
This changeset integrates the layer info cache with the registry webapp and
storage backend. The main benefit is to cache immutable layer meta data,
reducing backend roundtrips. The cache can be configured to use either redis or
an inmemory cache.

This provides massive performance benefits for HEAD http checks on layer blobs
and manifest verification.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
2015-04-02 20:15:16 -07:00

160 lines
4 KiB
Go

package storage
import (
"fmt"
ctxu "github.com/docker/distribution/context"
"github.com/docker/distribution/digest"
storagedriver "github.com/docker/distribution/registry/storage/driver"
"golang.org/x/net/context"
)
// 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 {
driver storagedriver.StorageDriver
pm *pathMapper
ctx context.Context
}
// 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 {
ctxu.GetLogger(bs.ctx).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
}