github.com/uriddle/docker@v0.0.0-20210926094723-4072e6aeb013/distribution/metadata/metadata.go (about)

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