distribution/docs/storage/layerwriter.go

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package storage
import (
"fmt"
"io"
"os"
"path"
"strconv"
"time"
"github.com/Sirupsen/logrus"
"github.com/docker/distribution"
ctxu "github.com/docker/distribution/context"
"github.com/docker/distribution/digest"
storagedriver "github.com/docker/distribution/registry/storage/driver"
)
var _ distribution.LayerUpload = &layerWriter{}
// layerWriter is used to control the various aspects of resumable
// layer upload. It implements the LayerUpload interface.
type layerWriter struct {
layerStore *layerStore
uuid string
startedAt time.Time
resumableDigester digest.ResumableDigester
// implementes io.WriteSeeker, io.ReaderFrom and io.Closer to satisfy
// LayerUpload Interface
bufferedFileWriter
}
var _ distribution.LayerUpload = &layerWriter{}
// UUID returns the identifier for this upload.
func (lw *layerWriter) UUID() string {
return lw.uuid
}
func (lw *layerWriter) StartedAt() time.Time {
return lw.startedAt
}
// Finish marks the upload as completed, returning a valid handle to the
// uploaded layer. The final size and checksum are validated against the
// contents of the uploaded layer. The checksum should be provided in the
// format <algorithm>:<hex digest>.
func (lw *layerWriter) Finish(digest digest.Digest) (distribution.Layer, error) {
ctxu.GetLogger(lw.layerStore.repository.ctx).Debug("(*layerWriter).Finish")
if err := lw.bufferedFileWriter.Close(); err != nil {
return nil, err
}
canonical, err := lw.validateLayer(digest)
if err != nil {
return nil, err
}
if err := lw.moveLayer(canonical); err != nil {
// TODO(stevvooe): Cleanup?
return nil, err
}
// Link the layer blob into the repository.
if err := lw.linkLayer(canonical, digest); err != nil {
return nil, err
}
if err := lw.removeResources(); err != nil {
return nil, err
}
return lw.layerStore.Fetch(canonical)
}
// Cancel the layer upload process.
func (lw *layerWriter) Cancel() error {
ctxu.GetLogger(lw.layerStore.repository.ctx).Debug("(*layerWriter).Cancel")
if err := lw.removeResources(); err != nil {
return err
}
lw.Close()
return nil
}
func (lw *layerWriter) Write(p []byte) (int, error) {
// Ensure that the current write offset matches how many bytes have been
// written to the digester. If not, we need to update the digest state to
// match the current write position.
if err := lw.resumeHashAt(lw.offset); err != nil {
return 0, err
}
return io.MultiWriter(&lw.bufferedFileWriter, lw.resumableDigester).Write(p)
}
func (lw *layerWriter) ReadFrom(r io.Reader) (n int64, err error) {
// Ensure that the current write offset matches how many bytes have been
// written to the digester. If not, we need to update the digest state to
// match the current write position.
if err := lw.resumeHashAt(lw.offset); err != nil {
return 0, err
}
return lw.bufferedFileWriter.ReadFrom(io.TeeReader(r, lw.resumableDigester))
}
func (lw *layerWriter) Close() error {
if err := lw.storeHashState(); err != nil {
return err
}
return lw.bufferedFileWriter.Close()
}
type hashStateEntry struct {
offset int64
path string
}
// getStoredHashStates returns a slice of hashStateEntries for this upload.
func (lw *layerWriter) getStoredHashStates() ([]hashStateEntry, error) {
uploadHashStatePathPrefix, err := lw.layerStore.repository.registry.pm.path(uploadHashStatePathSpec{
name: lw.layerStore.repository.Name(),
uuid: lw.uuid,
alg: lw.resumableDigester.Digest().Algorithm(),
list: true,
})
if err != nil {
return nil, err
}
paths, err := lw.driver.List(uploadHashStatePathPrefix)
if err != nil {
if _, ok := err.(storagedriver.PathNotFoundError); !ok {
return nil, err
}
// Treat PathNotFoundError as no entries.
paths = nil
}
hashStateEntries := make([]hashStateEntry, 0, len(paths))
for _, p := range paths {
pathSuffix := path.Base(p)
// The suffix should be the offset.
offset, err := strconv.ParseInt(pathSuffix, 0, 64)
if err != nil {
logrus.Errorf("unable to parse offset from upload state path %q: %s", p, err)
}
hashStateEntries = append(hashStateEntries, hashStateEntry{offset: offset, path: p})
}
return hashStateEntries, nil
}
// resumeHashAt attempts to restore the state of the internal hash function
// by loading the most recent saved hash state less than or equal to the given
// offset. Any unhashed bytes remaining less than the given offset are hashed
// from the content uploaded so far.
func (lw *layerWriter) resumeHashAt(offset int64) error {
if offset < 0 {
return fmt.Errorf("cannot resume hash at negative offset: %d", offset)
}
if offset == int64(lw.resumableDigester.Len()) {
// State of digester is already at the requseted offset.
return nil
}
// List hash states from storage backend.
var hashStateMatch hashStateEntry
hashStates, err := lw.getStoredHashStates()
if err != nil {
return fmt.Errorf("unable to get stored hash states with offset %d: %s", offset, err)
}
// Find the highest stored hashState with offset less than or equal to
// the requested offset.
for _, hashState := range hashStates {
if hashState.offset == offset {
hashStateMatch = hashState
break // Found an exact offset match.
} else if hashState.offset < offset && hashState.offset > hashStateMatch.offset {
// This offset is closer to the requested offset.
hashStateMatch = hashState
} else if hashState.offset > offset {
// Remove any stored hash state with offsets higher than this one
// as writes to this resumed hasher will make those invalid. This
// is probably okay to skip for now since we don't expect anyone to
// use the API in this way. For that reason, we don't treat an
// an error here as a fatal error, but only log it.
if err := lw.driver.Delete(hashState.path); err != nil {
logrus.Errorf("unable to delete stale hash state %q: %s", hashState.path, err)
}
}
}
if hashStateMatch.offset == 0 {
// No need to load any state, just reset the hasher.
lw.resumableDigester.Reset()
} else {
storedState, err := lw.driver.GetContent(hashStateMatch.path)
if err != nil {
return err
}
if err = lw.resumableDigester.Restore(storedState); err != nil {
return err
}
}
// Mind the gap.
if gapLen := offset - int64(lw.resumableDigester.Len()); gapLen > 0 {
// Need to read content from the upload to catch up to the desired
// offset.
fr, err := newFileReader(lw.driver, lw.path)
if err != nil {
return err
}
if _, err = fr.Seek(int64(lw.resumableDigester.Len()), os.SEEK_SET); err != nil {
return fmt.Errorf("unable to seek to layer reader offset %d: %s", lw.resumableDigester.Len(), err)
}
if _, err := io.CopyN(lw.resumableDigester, fr, gapLen); err != nil {
return err
}
}
return nil
}
func (lw *layerWriter) storeHashState() error {
uploadHashStatePath, err := lw.layerStore.repository.registry.pm.path(uploadHashStatePathSpec{
name: lw.layerStore.repository.Name(),
uuid: lw.uuid,
alg: lw.resumableDigester.Digest().Algorithm(),
offset: int64(lw.resumableDigester.Len()),
})
if err != nil {
return err
}
hashState, err := lw.resumableDigester.State()
if err != nil {
return err
}
return lw.driver.PutContent(uploadHashStatePath, hashState)
}
// validateLayer checks the layer data against the digest, returning an error
// if it does not match. The canonical digest is returned.
func (lw *layerWriter) validateLayer(dgst digest.Digest) (digest.Digest, error) {
// Restore the hasher state to the end of the upload.
if err := lw.resumeHashAt(lw.size); err != nil {
return "", err
}
var verified bool
canonical := lw.resumableDigester.Digest()
if canonical.Algorithm() == dgst.Algorithm() {
// Common case: client and server prefer the same canonical digest
// algorithm - currently SHA256.
verified = dgst == canonical
} else {
// The client wants to use a different digest algorithm. They'll just
// have to be patient and wait for us to download and re-hash the
// uploaded content using that digest algorithm.
digestVerifier, err := digest.NewDigestVerifier(dgst)
if err != nil {
return "", err
}
// Read the file from the backend driver and validate it.
fr, err := newFileReader(lw.bufferedFileWriter.driver, lw.path)
if err != nil {
return "", err
}
if _, err = io.Copy(digestVerifier, fr); err != nil {
return "", err
}
verified = digestVerifier.Verified()
}
if !verified {
return "", distribution.ErrLayerInvalidDigest{
Digest: dgst,
Reason: fmt.Errorf("content does not match digest"),
}
}
return canonical, nil
}
// moveLayer moves the data into its final, hash-qualified destination,
// identified by dgst. The layer should be validated before commencing the
// move.
func (lw *layerWriter) moveLayer(dgst digest.Digest) error {
blobPath, err := lw.layerStore.repository.registry.pm.path(blobDataPathSpec{
digest: dgst,
})
if err != nil {
return err
}
// Check for existence
if _, err := lw.driver.Stat(blobPath); err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
break // ensure that it doesn't exist.
default:
return err
}
} else {
// If the path exists, we can assume that the content has already
// been uploaded, since the blob storage is content-addressable.
// While it may be corrupted, detection of such corruption belongs
// elsewhere.
return nil
}
// If no data was received, we may not actually have a file on disk. Check
// the size here and write a zero-length file to blobPath if this is the
// case. For the most part, this should only ever happen with zero-length
// tars.
if _, err := lw.driver.Stat(lw.path); err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
// HACK(stevvooe): This is slightly dangerous: if we verify above,
// get a hash, then the underlying file is deleted, we risk moving
// a zero-length blob into a nonzero-length blob location. To
// prevent this horrid thing, we employ the hack of only allowing
// to this happen for the zero tarsum.
if dgst == digest.DigestSha256EmptyTar {
return lw.driver.PutContent(blobPath, []byte{})
}
// We let this fail during the move below.
logrus.
WithField("upload.uuid", lw.UUID()).
WithField("digest", dgst).Warnf("attempted to move zero-length content with non-zero digest")
default:
return err // unrelated error
}
}
return lw.driver.Move(lw.path, blobPath)
}
// linkLayer links a valid, written layer blob into the registry under the
// named repository for the upload controller.
func (lw *layerWriter) linkLayer(canonical digest.Digest, aliases ...digest.Digest) error {
dgsts := append([]digest.Digest{canonical}, aliases...)
// Don't make duplicate links.
seenDigests := make(map[digest.Digest]struct{}, len(dgsts))
for _, dgst := range dgsts {
if _, seen := seenDigests[dgst]; seen {
continue
}
seenDigests[dgst] = struct{}{}
layerLinkPath, err := lw.layerStore.repository.registry.pm.path(layerLinkPathSpec{
name: lw.layerStore.repository.Name(),
digest: dgst,
})
if err != nil {
return err
}
if err := lw.layerStore.repository.registry.driver.PutContent(layerLinkPath, []byte(canonical)); err != nil {
return err
}
}
return nil
}
// removeResources should clean up all resources associated with the upload
// instance. An error will be returned if the clean up cannot proceed. If the
// resources are already not present, no error will be returned.
func (lw *layerWriter) removeResources() error {
dataPath, err := lw.layerStore.repository.registry.pm.path(uploadDataPathSpec{
name: lw.layerStore.repository.Name(),
uuid: lw.uuid,
})
if err != nil {
return err
}
// Resolve and delete the containing directory, which should include any
// upload related files.
dirPath := path.Dir(dataPath)
if err := lw.driver.Delete(dirPath); err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
break // already gone!
default:
// This should be uncommon enough such that returning an error
// should be okay. At this point, the upload should be mostly
// complete, but perhaps the backend became unaccessible.
logrus.Errorf("unable to delete layer upload resources %q: %v", dirPath, err)
return err
}
}
return nil
}