moby/tag/store.go

package tag

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"sync"

	"github.com/docker/distribution/digest"
	"github.com/docker/distribution/reference"
	"github.com/docker/docker/image"
)

// DefaultTag defines the default tag used when performing images related actions and no tag string is specified
const DefaultTag = "latest"

var (
	// ErrDoesNotExist is returned if a reference is not found in the
	// store.
	ErrDoesNotExist = errors.New("reference does not exist")
)

// An Association is a tuple associating a reference with an image ID.
type Association struct {
	Ref     reference.Named
	ImageID image.ID
}

// Store provides the set of methods which can operate on a tag store.
type Store interface {
	References(id image.ID) []reference.Named
	ReferencesByName(ref reference.Named) []Association
	AddTag(ref reference.Named, id image.ID, force bool) error
	AddDigest(ref reference.Canonical, id image.ID, force bool) error
	Delete(ref reference.Named) (bool, error)
	Get(ref reference.Named) (image.ID, error)
}

type store struct {
	mu sync.RWMutex
	// jsonPath is the path to the file where the serialized tag data is
	// stored.
	jsonPath string
	// Repositories is a map of repositories, indexed by name.
	Repositories map[string]repository
	// referencesByIDCache is a cache of references indexed by ID, to speed
	// up References.
	referencesByIDCache map[image.ID]map[string]reference.Named
}

// Repository maps tags to image IDs. The key is a a stringified Reference,
// including the repository name.
type repository map[string]image.ID

func defaultTagIfNameOnly(ref reference.Named) reference.Named {
	switch ref.(type) {
	case reference.Tagged:
		return ref
	case reference.Digested:
		return ref
	default:
		// Should never fail
		ref, _ = reference.WithTag(ref, DefaultTag)
		return ref
	}
}

// NewTagStore creates a new tag store, tied to a file path where the set of
// tags is serialized in JSON format.
func NewTagStore(jsonPath string) (Store, error) {
	abspath, err := filepath.Abs(jsonPath)
	if err != nil {
		return nil, err
	}

	store := &store{
		jsonPath:            abspath,
		Repositories:        make(map[string]repository),
		referencesByIDCache: make(map[image.ID]map[string]reference.Named),
	}
	// Load the json file if it exists, otherwise create it.
	if err := store.reload(); os.IsNotExist(err) {
		if err := store.save(); err != nil {
			return nil, err
		}
	} else if err != nil {
		return nil, err
	}
	return store, nil
}

// Add adds a tag to the store. If force is set to true, existing
// references can be overwritten. This only works for tags, not digests.
func (store *store) AddTag(ref reference.Named, id image.ID, force bool) error {
	if _, isDigested := ref.(reference.Digested); isDigested {
		return errors.New("refusing to create a tag with a digest reference")
	}
	return store.addReference(defaultTagIfNameOnly(ref), id, force)
}

// Add adds a digest reference to the store.
func (store *store) AddDigest(ref reference.Canonical, id image.ID, force bool) error {
	return store.addReference(ref, id, force)
}

func (store *store) addReference(ref reference.Named, id image.ID, force bool) error {
	if ref.Name() == string(digest.Canonical) {
		return errors.New("refusing to create an ambiguous tag using digest algorithm as name")
	}

	store.mu.Lock()
	defer store.mu.Unlock()

	repository, exists := store.Repositories[ref.Name()]
	if !exists || repository == nil {
		repository = make(map[string]image.ID)
		store.Repositories[ref.Name()] = repository
	}

	refStr := ref.String()
	oldID, exists := repository[refStr]

	if exists {
		// force only works for tags
		if digested, isDigest := ref.(reference.Digested); isDigest {
			return fmt.Errorf("Cannot overwrite digest %s", digested.Digest().String())
		}

		if !force {
			return fmt.Errorf("Conflict: Tag %s is already set to image %s, if you want to replace it, please use -f option", ref.String(), oldID.String())
		}

		if store.referencesByIDCache[oldID] != nil {
			delete(store.referencesByIDCache[oldID], refStr)
			if len(store.referencesByIDCache[oldID]) == 0 {
				delete(store.referencesByIDCache, oldID)
			}
		}
	}

	repository[refStr] = id
	if store.referencesByIDCache[id] == nil {
		store.referencesByIDCache[id] = make(map[string]reference.Named)
	}
	store.referencesByIDCache[id][refStr] = ref

	return store.save()
}

// Delete deletes a reference from the store. It returns true if a deletion
// happened, or false otherwise.
func (store *store) Delete(ref reference.Named) (bool, error) {
	ref = defaultTagIfNameOnly(ref)

	store.mu.Lock()
	defer store.mu.Unlock()

	repoName := ref.Name()

	repository, exists := store.Repositories[repoName]
	if !exists {
		return false, ErrDoesNotExist
	}

	refStr := ref.String()
	if id, exists := repository[refStr]; exists {
		delete(repository, refStr)
		if len(repository) == 0 {
			delete(store.Repositories, repoName)
		}
		if store.referencesByIDCache[id] != nil {
			delete(store.referencesByIDCache[id], refStr)
			if len(store.referencesByIDCache[id]) == 0 {
				delete(store.referencesByIDCache, id)
			}
		}
		return true, store.save()
	}

	return false, ErrDoesNotExist
}

// Get retrieves an item from the store by reference.
func (store *store) Get(ref reference.Named) (image.ID, error) {
	ref = defaultTagIfNameOnly(ref)

	store.mu.RLock()
	defer store.mu.RUnlock()

	repository, exists := store.Repositories[ref.Name()]
	if !exists || repository == nil {
		return "", ErrDoesNotExist
	}

	id, exists := repository[ref.String()]
	if !exists {
		return "", ErrDoesNotExist
	}

	return id, nil
}

// References returns a slice of references to the given image ID. The slice
// will be nil if there are no references to this image ID.
func (store *store) References(id image.ID) []reference.Named {
	store.mu.RLock()
	defer store.mu.RUnlock()

	// Convert the internal map to an array for two reasons:
	// 1) We must not return a mutable reference.
	// 2) It would be ugly to expose the extraneous map keys to callers.

	var references []reference.Named
	for _, ref := range store.referencesByIDCache[id] {
		references = append(references, ref)
	}

	return references
}

// ReferencesByName returns the references for a given repository name.
// If there are no references known for this repository name,
// ReferencesByName returns nil.
func (store *store) ReferencesByName(ref reference.Named) []Association {
	store.mu.RLock()
	defer store.mu.RUnlock()

	repository, exists := store.Repositories[ref.Name()]
	if !exists {
		return nil
	}

	var associations []Association
	for refStr, refID := range repository {
		ref, err := reference.ParseNamed(refStr)
		if err != nil {
			// Should never happen
			return nil
		}
		associations = append(associations,
			Association{
				Ref:     ref,
				ImageID: refID,
			})
	}

	return associations
}

func (store *store) save() error {
	// Store the json
	jsonData, err := json.Marshal(store)
	if err != nil {
		return err
	}

	tempFilePath := store.jsonPath + ".tmp"

	if err := ioutil.WriteFile(tempFilePath, jsonData, 0600); err != nil {
		return err
	}

	if err := os.Rename(tempFilePath, store.jsonPath); err != nil {
		return err
	}

	return nil
}

func (store *store) reload() error {
	f, err := os.Open(store.jsonPath)
	if err != nil {
		return err
	}
	defer f.Close()
	if err := json.NewDecoder(f).Decode(&store); err != nil {
		return err
	}

	for _, repository := range store.Repositories {
		for refStr, refID := range repository {
			ref, err := reference.ParseNamed(refStr)
			if err != nil {
				// Should never happen
				continue
			}
			if store.referencesByIDCache[refID] == nil {
				store.referencesByIDCache[refID] = make(map[string]reference.Named)
			}
			store.referencesByIDCache[refID][refStr] = ref
		}
	}

	return nil
}