distribution/registry/storage/cache/cache.go

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// Package cache provides facilities to speed up access to the storage
// backend. Typically cache implementations deal with internal implementation
// details at the backend level, rather than generalized caches for
// distribution related interfaces. In other words, unless the cache is
// specific to the storage package, it belongs in another package.
package cache
import (
"fmt"
"github.com/docker/distribution/digest"
"golang.org/x/net/context"
)
// ErrNotFound is returned when a meta item is not found.
var ErrNotFound = fmt.Errorf("not found")
// LayerMeta describes the backend location and length of layer data.
type LayerMeta struct {
Path string
Length int64
}
// LayerInfoCache is a driver-aware cache of layer metadata. Basically, it
// provides a fast cache for checks against repository metadata, avoiding
// round trips to backend storage. Note that this is different from a pure
// layer cache, which would also provide access to backing data, as well. Such
// a cache should be implemented as a middleware, rather than integrated with
// the storage backend.
//
// Note that most implementations rely on the caller to do strict checks on on
// repo and dgst arguments, since these are mostly used behind existing
// implementations.
type LayerInfoCache interface {
// Contains returns true if the repository with name contains the layer.
Contains(ctx context.Context, repo string, dgst digest.Digest) (bool, error)
// Add includes the layer in the given repository cache.
Add(ctx context.Context, repo string, dgst digest.Digest) error
// Meta provides the location of the layer on the backend and its size. Membership of a
// repository should be tested before using the result, if required.
Meta(ctx context.Context, dgst digest.Digest) (LayerMeta, error)
// SetMeta sets the meta data for the given layer.
SetMeta(ctx context.Context, dgst digest.Digest, meta LayerMeta) error
}
// base implements common checks between cache implementations. Note that
// these are not full checks of input, since that should be done by the
// caller.
type base struct {
LayerInfoCache
}
func (b *base) Contains(ctx context.Context, repo string, dgst digest.Digest) (bool, error) {
if repo == "" {
return false, fmt.Errorf("cache: cannot check for empty repository name")
}
if dgst == "" {
return false, fmt.Errorf("cache: cannot check for empty digests")
}
return b.LayerInfoCache.Contains(ctx, repo, dgst)
}
func (b *base) Add(ctx context.Context, repo string, dgst digest.Digest) error {
if repo == "" {
return fmt.Errorf("cache: cannot add empty repository name")
}
if dgst == "" {
return fmt.Errorf("cache: cannot add empty digest")
}
return b.LayerInfoCache.Add(ctx, repo, dgst)
}
func (b *base) Meta(ctx context.Context, dgst digest.Digest) (LayerMeta, error) {
if dgst == "" {
return LayerMeta{}, fmt.Errorf("cache: cannot get meta for empty digest")
}
return b.LayerInfoCache.Meta(ctx, dgst)
}
func (b *base) SetMeta(ctx context.Context, dgst digest.Digest, meta LayerMeta) error {
if dgst == "" {
return fmt.Errorf("cache: cannot set meta for empty digest")
}
if meta.Path == "" {
return fmt.Errorf("cache: cannot set empty path for meta")
}
return b.LayerInfoCache.SetMeta(ctx, dgst, meta)
}