distribution/docs/storage/blobwriter.go
Stephen J Day a0d242d9df Remove digest package's dependency on external sha implementation
The change relies on a refactor of the upstream resumable sha256/sha512 package
that opts to register implementations with the standard library. This allows
the resumable support to be detected where it matters, avoiding unnecessary and
complex code. It also ensures that consumers of the digest package don't need
to depend on the forked sha implementations.

We also get an optimization with this change. If the size of data written to a
digester is the same as the file size, we check to see if the digest has been
verified. This works if the blob is written and committed in a single request.

Signed-off-by: Stephen J Day <stephen.day@docker.com>
2015-05-20 23:44:08 -07:00

312 lines
9.3 KiB
Go

package storage
import (
"fmt"
"io"
"time"
"github.com/Sirupsen/logrus"
"github.com/docker/distribution"
"github.com/docker/distribution/context"
"github.com/docker/distribution/digest"
storagedriver "github.com/docker/distribution/registry/storage/driver"
)
var (
errResumableDigestNotAvailable = fmt.Errorf("resumable digest not available")
)
// layerWriter is used to control the various aspects of resumable
// layer upload. It implements the LayerUpload interface.
type blobWriter struct {
blobStore *linkedBlobStore
id string
startedAt time.Time
digester digest.Digester
written int64 // track the contiguous write
// implementes io.WriteSeeker, io.ReaderFrom and io.Closer to satisfy
// LayerUpload Interface
bufferedFileWriter
}
var _ distribution.BlobWriter = &blobWriter{}
// ID returns the identifier for this upload.
func (bw *blobWriter) ID() string {
return bw.id
}
func (bw *blobWriter) StartedAt() time.Time {
return bw.startedAt
}
// Commit marks the upload as completed, returning a valid descriptor. The
// final size and digest are checked against the first descriptor provided.
func (bw *blobWriter) Commit(ctx context.Context, desc distribution.Descriptor) (distribution.Descriptor, error) {
context.GetLogger(ctx).Debug("(*blobWriter).Commit")
if err := bw.bufferedFileWriter.Close(); err != nil {
return distribution.Descriptor{}, err
}
canonical, err := bw.validateBlob(ctx, desc)
if err != nil {
return distribution.Descriptor{}, err
}
if err := bw.moveBlob(ctx, canonical); err != nil {
return distribution.Descriptor{}, err
}
if err := bw.blobStore.linkBlob(ctx, canonical, desc.Digest); err != nil {
return distribution.Descriptor{}, err
}
if err := bw.removeResources(ctx); err != nil {
return distribution.Descriptor{}, err
}
return canonical, nil
}
// Rollback the blob upload process, releasing any resources associated with
// the writer and canceling the operation.
func (bw *blobWriter) Cancel(ctx context.Context) error {
context.GetLogger(ctx).Debug("(*blobWriter).Rollback")
if err := bw.removeResources(ctx); err != nil {
return err
}
bw.Close()
return nil
}
func (bw *blobWriter) 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 := bw.resumeDigestAt(bw.blobStore.ctx, bw.offset); err != nil && err != errResumableDigestNotAvailable {
return 0, err
}
n, err := io.MultiWriter(&bw.bufferedFileWriter, bw.digester.Hash()).Write(p)
bw.written += int64(n)
return n, err
}
func (bw *blobWriter) 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 := bw.resumeDigestAt(bw.blobStore.ctx, bw.offset); err != nil && err != errResumableDigestNotAvailable {
return 0, err
}
nn, err := bw.bufferedFileWriter.ReadFrom(io.TeeReader(r, bw.digester.Hash()))
bw.written += nn
return nn, err
}
func (bw *blobWriter) Close() error {
if bw.err != nil {
return bw.err
}
if err := bw.storeHashState(bw.blobStore.ctx); err != nil {
return err
}
return bw.bufferedFileWriter.Close()
}
// validateBlob checks the data against the digest, returning an error if it
// does not match. The canonical descriptor is returned.
func (bw *blobWriter) validateBlob(ctx context.Context, desc distribution.Descriptor) (distribution.Descriptor, error) {
var (
verified, fullHash bool
canonical digest.Digest
)
if desc.Digest == "" {
// if no descriptors are provided, we have nothing to validate
// against. We don't really want to support this for the registry.
return distribution.Descriptor{}, distribution.ErrBlobInvalidDigest{
Reason: fmt.Errorf("cannot validate against empty digest"),
}
}
// Stat the on disk file
if fi, err := bw.bufferedFileWriter.driver.Stat(ctx, bw.path); err != nil {
switch err := err.(type) {
case storagedriver.PathNotFoundError:
// NOTE(stevvooe): We really don't care if the file is
// not actually present for the reader. We now assume
// that the desc length is zero.
desc.Length = 0
default:
// Any other error we want propagated up the stack.
return distribution.Descriptor{}, err
}
} else {
if fi.IsDir() {
return distribution.Descriptor{}, fmt.Errorf("unexpected directory at upload location %q", bw.path)
}
bw.size = fi.Size()
}
if desc.Length > 0 {
if desc.Length != bw.size {
return distribution.Descriptor{}, distribution.ErrBlobInvalidLength
}
} else {
// if provided 0 or negative length, we can assume caller doesn't know or
// care about length.
desc.Length = bw.size
}
// TODO(stevvooe): This section is very meandering. Need to be broken down
// to be a lot more clear.
if err := bw.resumeDigestAt(ctx, bw.size); err == nil {
canonical = bw.digester.Digest()
if canonical.Algorithm() == desc.Digest.Algorithm() {
// Common case: client and server prefer the same canonical digest
// algorithm - currently SHA256.
verified = desc.Digest == 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.
fullHash = true
}
} else if err == errResumableDigestNotAvailable {
// Not using resumable digests, so we need to hash the entire layer.
fullHash = true
} else {
return distribution.Descriptor{}, err
}
if fullHash {
// a fantastic optimization: if the the written data and the size are
// the same, we don't need to read the data from the backend. This is
// because we've written the entire file in the lifecycle of the
// current instance.
if bw.written == bw.size && digest.CanonicalAlgorithm == desc.Digest.Algorithm() {
canonical = bw.digester.Digest()
verified = desc.Digest == canonical
}
// If the check based on size fails, we fall back to the slowest of
// paths. We may be able to make the size-based check a stronger
// guarantee, so this may be defensive.
if !verified {
digester := digest.NewCanonicalDigester()
digestVerifier, err := digest.NewDigestVerifier(desc.Digest)
if err != nil {
return distribution.Descriptor{}, err
}
// Read the file from the backend driver and validate it.
fr, err := newFileReader(ctx, bw.bufferedFileWriter.driver, bw.path, desc.Length)
if err != nil {
return distribution.Descriptor{}, err
}
tr := io.TeeReader(fr, digester.Hash())
if _, err := io.Copy(digestVerifier, tr); err != nil {
return distribution.Descriptor{}, err
}
canonical = digester.Digest()
verified = digestVerifier.Verified()
}
}
if !verified {
context.GetLoggerWithFields(ctx,
map[string]interface{}{
"canonical": canonical,
"provided": desc.Digest,
}, "canonical", "provided").
Errorf("canonical digest does match provided digest")
return distribution.Descriptor{}, distribution.ErrBlobInvalidDigest{
Digest: desc.Digest,
Reason: fmt.Errorf("content does not match digest"),
}
}
// update desc with canonical hash
desc.Digest = canonical
if desc.MediaType == "" {
desc.MediaType = "application/octet-stream"
}
return desc, nil
}
// moveBlob moves the data into its final, hash-qualified destination,
// identified by dgst. The layer should be validated before commencing the
// move.
func (bw *blobWriter) moveBlob(ctx context.Context, desc distribution.Descriptor) error {
blobPath, err := bw.blobStore.pm.path(blobDataPathSpec{
digest: desc.Digest,
})
if err != nil {
return err
}
// Check for existence
if _, err := bw.blobStore.driver.Stat(ctx, 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 := bw.blobStore.driver.Stat(ctx, bw.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 desc.Digest == digest.DigestSha256EmptyTar {
return bw.blobStore.driver.PutContent(ctx, blobPath, []byte{})
}
// We let this fail during the move below.
logrus.
WithField("upload.id", bw.ID()).
WithField("digest", desc.Digest).Warnf("attempted to move zero-length content with non-zero digest")
default:
return err // unrelated error
}
}
// TODO(stevvooe): We should also write the mediatype when executing this move.
return bw.blobStore.driver.Move(ctx, bw.path, blobPath)
}