github.com/lazyboychen7/engine@v17.12.1-ce-rc2+incompatible/distribution/metadata/metadata.go (about)

     1  package metadata
     2  
     3  import (
     4  	"io/ioutil"
     5  	"os"
     6  	"path/filepath"
     7  	"sync"
     8  
     9  	"github.com/docker/docker/pkg/ioutils"
    10  )
    11  
    12  // Store implements a K/V store for mapping distribution-related IDs
    13  // to on-disk layer IDs and image IDs. The namespace identifies the type of
    14  // mapping (i.e. "v1ids" or "artifacts"). MetadataStore is goroutine-safe.
    15  type Store interface {
    16  	// Get retrieves data by namespace and key.
    17  	Get(namespace string, key string) ([]byte, error)
    18  	// Set writes data indexed by namespace and key.
    19  	Set(namespace, key string, value []byte) error
    20  	// Delete removes data indexed by namespace and key.
    21  	Delete(namespace, key string) error
    22  }
    23  
    24  // FSMetadataStore uses the filesystem to associate metadata with layer and
    25  // image IDs.
    26  type FSMetadataStore struct {
    27  	sync.RWMutex
    28  	basePath string
    29  	platform string
    30  }
    31  
    32  // NewFSMetadataStore creates a new filesystem-based metadata store.
    33  func NewFSMetadataStore(basePath, platform string) (*FSMetadataStore, error) {
    34  	if err := os.MkdirAll(basePath, 0700); err != nil {
    35  		return nil, err
    36  	}
    37  	return &FSMetadataStore{
    38  		basePath: basePath,
    39  		platform: platform,
    40  	}, nil
    41  }
    42  
    43  func (store *FSMetadataStore) path(namespace, key string) string {
    44  	return filepath.Join(store.basePath, namespace, key)
    45  }
    46  
    47  // Get retrieves data by namespace and key. The data is read from a file named
    48  // after the key, stored in the namespace's directory.
    49  func (store *FSMetadataStore) Get(namespace string, key string) ([]byte, error) {
    50  	store.RLock()
    51  	defer store.RUnlock()
    52  
    53  	return ioutil.ReadFile(store.path(namespace, key))
    54  }
    55  
    56  // Set writes data indexed by namespace and key. The data is written to a file
    57  // named after the key, stored in the namespace's directory.
    58  func (store *FSMetadataStore) Set(namespace, key string, value []byte) error {
    59  	store.Lock()
    60  	defer store.Unlock()
    61  
    62  	path := store.path(namespace, key)
    63  	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
    64  		return err
    65  	}
    66  	return ioutils.AtomicWriteFile(path, value, 0644)
    67  }
    68  
    69  // Delete removes data indexed by namespace and key. The data file named after
    70  // the key, stored in the namespace's directory is deleted.
    71  func (store *FSMetadataStore) Delete(namespace, key string) error {
    72  	store.Lock()
    73  	defer store.Unlock()
    74  
    75  	path := store.path(namespace, key)
    76  	return os.Remove(path)
    77  }