dotcloud/docker

package metadata // import "github.com/docker/docker/distribution/metadata"

import (
    "os"
    "path/filepath"
    "sync"

    "github.com/docker/docker/pkg/ioutils"
)

// Store implements a K/V store for mapping distribution-related IDs
// to on-disk layer IDs and image IDs. The namespace identifies the type of
// mapping (i.e. "v1ids" or "artifacts"). MetadataStore is goroutine-safe.
type Store interface {
    // Get retrieves data by namespace and key.
    Get(namespace string, key string) ([]byte, error)
    // Set writes data indexed by namespace and key.
    Set(namespace, key string, value []byte) error
    // Delete removes data indexed by namespace and key.
    Delete(namespace, key string) error
}

// FSMetadataStore uses the filesystem to associate metadata with layer and
// image IDs.
type FSMetadataStore struct {
    sync.RWMutex
    basePath string
}

// NewFSMetadataStore creates a new filesystem-based metadata store.
func NewFSMetadataStore(basePath string) (*FSMetadataStore, error) {
    if err := os.MkdirAll(basePath, 0o700); err != nil {
        return nil, err
    }
    return &FSMetadataStore{
        basePath: basePath,
    }, nil
}

func (store *FSMetadataStore) path(namespace, key string) string {
    return filepath.Join(store.basePath, namespace, key)
}

// Get retrieves data by namespace and key. The data is read from a file named
// after the key, stored in the namespace's directory.
func (store *FSMetadataStore) Get(namespace string, key string) ([]byte, error) {
    store.RLock()
    defer store.RUnlock()

    return os.ReadFile(store.path(namespace, key))
}

// Set writes data indexed by namespace and key. The data is written to a file
// named after the key, stored in the namespace's directory.
func (store *FSMetadataStore) Set(namespace, key string, value []byte) error {
    store.Lock()
    defer store.Unlock()

    path := store.path(namespace, key)
    if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
        return err
    }
    return ioutils.AtomicWriteFile(path, value, 0o644)
}

// Delete removes data indexed by namespace and key. The data file named after
// the key, stored in the namespace's directory is deleted.
func (store *FSMetadataStore) Delete(namespace, key string) error {
    store.Lock()
    defer store.Unlock()

    path := store.path(namespace, key)
    return os.Remove(path)
}