// schema2ManifestDigest computes the manifest digest, and, if pulling by
// digest, ensures that it matches the requested digest.
func schema2ManifestDigest(ref reference.Named, mfst distribution.Manifest) (digest.Digest, error) {
	_, canonical, err := mfst.Payload()
	if err != nil {
		return "", err
	}

	// If pull by digest, then verify the manifest digest.
	if digested, isDigested := ref.(reference.Canonical); isDigested {
		verifier, err := digest.NewDigestVerifier(digested.Digest())
		if err != nil {
			return "", err
		}
		if _, err := verifier.Write(canonical); err != nil {
			return "", err
		}
		if !verifier.Verified() {
			err := fmt.Errorf("manifest verification failed for digest %s", digested.Digest())
			logrus.Error(err)
			return "", err
		}
		return digested.Digest(), nil
	}

	return digest.FromBytes(canonical), nil
}

// Verify reads the given reader in to a temporary file and validates that
// it matches the digest. If it does, it returns a reader for that allows access
// to the data. Otherwise, it returns an error.
// The caller is responsible for closing the returned reader, in order to
// ensure the temporary file is deleted.
func Verify(r io.Reader, d digest.Digest) (io.ReadCloser, error) {
	w, err := digest.NewDigestVerifier(d)
	if err != nil {
		return nil, err
	}

	tmp, err := ioutil.TempFile("", "unverified-layer")
	if err != nil {
		return nil, err
	}

	_, err = io.Copy(io.MultiWriter(w, tmp), r)
	if err != nil {
		return nil, err
	}

	if !w.Verified() {
		return nil, errors.New("digest verification failed")
	}

	_, err = tmp.Seek(0, 0)
	if err != nil {
		return nil, err
	}

	return &deleteCloser{tmp}, nil
}

func verifySchema1Manifest(signedManifest *schema1.SignedManifest, ref reference.Named) (m *schema1.Manifest, err error) {
	// If pull by digest, then verify the manifest digest. NOTE: It is
	// important to do this first, before any other content validation. If the
	// digest cannot be verified, don't even bother with those other things.
	if digested, isCanonical := ref.(reference.Canonical); isCanonical {
		verifier, err := digest.NewDigestVerifier(digested.Digest())
		if err != nil {
			return nil, err
		}
		if _, err := verifier.Write(signedManifest.Canonical); err != nil {
			return nil, err
		}
		if !verifier.Verified() {
			err := fmt.Errorf("image verification failed for digest %s", digested.Digest())
			logrus.Error(err)
			return nil, err
		}
	}
	m = &signedManifest.Manifest

	if m.SchemaVersion != 1 {
		return nil, fmt.Errorf("unsupported schema version %d for %q", m.SchemaVersion, ref.String())
	}
	if len(m.FSLayers) != len(m.History) {
		return nil, fmt.Errorf("length of history not equal to number of layers for %q", ref.String())
	}
	if len(m.FSLayers) == 0 {
		return nil, fmt.Errorf("no FSLayers in manifest for %q", ref.String())
	}
	return m, nil
}

// ManifestMatchesImage returns true if the provided manifest matches the name of the image.
func ManifestMatchesImage(image *Image, newManifest []byte) (bool, error) {
	dgst, err := digest.ParseDigest(image.Name)
	if err != nil {
		return false, err
	}
	v, err := digest.NewDigestVerifier(dgst)
	if err != nil {
		return false, err
	}
	var canonical []byte

	switch image.DockerImageManifestMediaType {
	case schema2.MediaTypeManifest:
		var m schema2.DeserializedManifest
		if err := json.Unmarshal(newManifest, &m); err != nil {
			return false, err
		}
		_, canonical, err = m.Payload()
		if err != nil {
			return false, err
		}
	case schema1.MediaTypeManifest, "":
		var m schema1.SignedManifest
		if err := json.Unmarshal(newManifest, &m); err != nil {
			return false, err
		}
		canonical = m.Canonical
	default:
		return false, fmt.Errorf("unsupported manifest mediatype: %s", image.DockerImageManifestMediaType)
	}
	if _, err := v.Write(canonical); err != nil {
		return false, err
	}
	return v.Verified(), nil
}

// GetRemoteCA returns the remote endpoint's CA certificate
func GetRemoteCA(ctx context.Context, d digest.Digest, picker *picker.Picker) (RootCA, error) {
	// We need a valid picker to be able to Dial to a remote CA
	if picker == nil {
		return RootCA{}, fmt.Errorf("valid remote address picker required")
	}

	// This TLS Config is intentionally using InsecureSkipVerify. Either we're
	// doing TOFU, in which case we don't validate the remote CA, or we're using
	// a user supplied hash to check the integrity of the CA certificate.
	insecureCreds := credentials.NewTLS(&tls.Config{InsecureSkipVerify: true})
	opts := []grpc.DialOption{
		grpc.WithTransportCredentials(insecureCreds),
		grpc.WithBackoffMaxDelay(10 * time.Second),
		grpc.WithPicker(picker)}

	firstAddr, err := picker.PickAddr()
	if err != nil {
		return RootCA{}, err
	}

	conn, err := grpc.Dial(firstAddr, opts...)
	if err != nil {
		return RootCA{}, err
	}
	defer conn.Close()

	client := api.NewCAClient(conn)
	response, err := client.GetRootCACertificate(ctx, &api.GetRootCACertificateRequest{})
	if err != nil {
		return RootCA{}, err
	}

	if d != "" {
		verifier, err := digest.NewDigestVerifier(d)
		if err != nil {
			return RootCA{}, fmt.Errorf("unexpected error getting digest verifier: %v", err)
		}

		io.Copy(verifier, bytes.NewReader(response.Certificate))

		if !verifier.Verified() {
			return RootCA{}, fmt.Errorf("remote CA does not match fingerprint. Expected: %s", d.Hex())

		}
	}

	// Check the validity of the remote Cert
	_, err = helpers.ParseCertificatePEM(response.Certificate)
	if err != nil {
		return RootCA{}, err
	}

	// Create a Pool with our RootCACertificate
	pool := x509.NewCertPool()
	if !pool.AppendCertsFromPEM(response.Certificate) {
		return RootCA{}, fmt.Errorf("failed to append certificate to cert pool")
	}

	return RootCA{Cert: response.Certificate, Pool: pool}, nil
}

func (p *v2Puller) download(di *downloadInfo) {
	logrus.Debugf("pulling blob %q", di.digest)

	blobs := p.repo.Blobs(context.Background())

	desc, err := blobs.Stat(context.Background(), di.digest)
	if err != nil {
		logrus.Debugf("Error statting layer: %v", err)
		di.err <- err
		return
	}
	di.size = desc.Size

	layerDownload, err := blobs.Open(context.Background(), di.digest)
	if err != nil {
		logrus.Debugf("Error fetching layer: %v", err)
		di.err <- err
		return
	}
	defer layerDownload.Close()

	verifier, err := digest.NewDigestVerifier(di.digest)
	if err != nil {
		di.err <- err
		return
	}

	digestStr := di.digest.String()

	reader := progressreader.New(progressreader.Config{
		In:        ioutil.NopCloser(io.TeeReader(layerDownload, verifier)),
		Out:       di.broadcaster,
		Formatter: p.sf,
		Size:      di.size,
		NewLines:  false,
		ID:        stringid.TruncateID(digestStr),
		Action:    "Downloading",
	})
	io.Copy(di.tmpFile, reader)

	di.broadcaster.Write(p.sf.FormatProgress(stringid.TruncateID(digestStr), "Verifying Checksum", nil))

	if !verifier.Verified() {
		err = fmt.Errorf("filesystem layer verification failed for digest %s", di.digest)
		logrus.Error(err)
		di.err <- err
		return
	}

	di.broadcaster.Write(p.sf.FormatProgress(stringid.TruncateID(digestStr), "Download complete", nil))

	logrus.Debugf("Downloaded %s to tempfile %s", digestStr, di.tmpFile.Name())
	di.layer = layerDownload

	di.err <- nil
}

func newVerifiedReadCloser(rc io.ReadCloser, dgst digest.Digest) (io.ReadCloser, error) {
	verifier, err := digest.NewDigestVerifier(dgst)
	if err != nil {
		return nil, err
	}
	return &verifiedReadCloser{
		rc:       rc,
		dgst:     dgst,
		verifier: verifier,
	}, nil
}

// GetRemoteCA returns the remote endpoint's CA certificate
func GetRemoteCA(ctx context.Context, d digest.Digest, r remotes.Remotes) (RootCA, error) {
	// This TLS Config is intentionally using InsecureSkipVerify. We use the
	// digest instead to check the integrity of the CA certificate.
	insecureCreds := credentials.NewTLS(&tls.Config{InsecureSkipVerify: true})
	conn, peer, err := getGRPCConnection(insecureCreds, r)
	if err != nil {
		return RootCA{}, err
	}
	defer conn.Close()

	client := api.NewCAClient(conn)
	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	defer func() {
		if err != nil {
			r.Observe(peer, -remotes.DefaultObservationWeight)
			return
		}
		r.Observe(peer, remotes.DefaultObservationWeight)
	}()
	response, err := client.GetRootCACertificate(ctx, &api.GetRootCACertificateRequest{})
	if err != nil {
		return RootCA{}, err
	}

	if d != "" {
		verifier, err := digest.NewDigestVerifier(d)
		if err != nil {
			return RootCA{}, errors.Wrap(err, "unexpected error getting digest verifier")
		}

		io.Copy(verifier, bytes.NewReader(response.Certificate))

		if !verifier.Verified() {
			return RootCA{}, errors.Errorf("remote CA does not match fingerprint. Expected: %s", d.Hex())

		}
	}

	// Check the validity of the remote Cert
	_, err = helpers.ParseCertificatePEM(response.Certificate)
	if err != nil {
		return RootCA{}, err
	}

	// Create a Pool with our RootCACertificate
	pool := x509.NewCertPool()
	if !pool.AppendCertsFromPEM(response.Certificate) {
		return RootCA{}, errors.New("failed to append certificate to cert pool")
	}

	return RootCA{Cert: response.Certificate, Digest: digest.FromBytes(response.Certificate), Pool: pool}, nil
}

// Finally Push the (signed) manifest of the blobs we've just pushed
func (r *Session) PutV2ImageManifest(ep *Endpoint, imageName, tagName string, signedManifest, rawManifest []byte, auth *RequestAuthorization) (digest.Digest, error) {
	routeURL, err := getV2Builder(ep).BuildManifestURL(imageName, tagName)
	if err != nil {
		return "", err
	}

	method := "PUT"
	logrus.Debugf("[registry] Calling %q %s", method, routeURL)
	req, err := http.NewRequest(method, routeURL, bytes.NewReader(signedManifest))
	if err != nil {
		return "", err
	}
	if err := auth.Authorize(req); err != nil {
		return "", err
	}
	res, err := r.client.Do(req)
	if err != nil {
		return "", err
	}
	defer res.Body.Close()

	// All 2xx and 3xx responses can be accepted for a put.
	if res.StatusCode >= 400 {
		if res.StatusCode == 401 {
			return "", errLoginRequired
		}
		errBody, err := ioutil.ReadAll(res.Body)
		if err != nil {
			return "", err
		}
		logrus.Debugf("Unexpected response from server: %q %#v", errBody, res.Header)
		return "", httputils.NewHTTPRequestError(fmt.Sprintf("Server error: %d trying to push %s:%s manifest", res.StatusCode, imageName, tagName), res)
	}

	hdrDigest, err := digest.ParseDigest(res.Header.Get(DockerDigestHeader))
	if err != nil {
		return "", fmt.Errorf("invalid manifest digest from registry: %s", err)
	}

	dgstVerifier, err := digest.NewDigestVerifier(hdrDigest)
	if err != nil {
		return "", fmt.Errorf("invalid manifest digest from registry: %s", err)
	}

	dgstVerifier.Write(rawManifest)

	if !dgstVerifier.Verified() {
		computedDigest, _ := digest.FromBytes(rawManifest)
		return "", fmt.Errorf("unable to verify manifest digest: registry has %q, computed %q", hdrDigest, computedDigest)
	}

	return hdrDigest, nil
}

func (p *v2Puller) validateManifest(m *manifest.SignedManifest, tag string) (verified bool, err error) {
	// If pull by digest, then verify the manifest digest. NOTE: It is
	// important to do this first, before any other content validation. If the
	// digest cannot be verified, don't even bother with those other things.
	if manifestDigest, err := digest.ParseDigest(tag); err == nil {
		verifier, err := digest.NewDigestVerifier(manifestDigest)
		if err != nil {
			return false, err
		}
		payload, err := m.Payload()
		if err != nil {
			return false, err
		}
		if _, err := verifier.Write(payload); err != nil {
			return false, err
		}
		if !verifier.Verified() {
			err := fmt.Errorf("image verification failed for digest %s", manifestDigest)
			logrus.Error(err)
			return false, err
		}
	}

	// TODO(tiborvass): what's the usecase for having manifest == nil and err == nil ? Shouldn't be the error be "DoesNotExist" ?
	if m == nil {
		return false, fmt.Errorf("image manifest does not exist for tag %q", tag)
	}
	if m.SchemaVersion != 1 {
		return false, fmt.Errorf("unsupported schema version %d for tag %q", m.SchemaVersion, tag)
	}
	if len(m.FSLayers) != len(m.History) {
		return false, fmt.Errorf("length of history not equal to number of layers for tag %q", tag)
	}
	if len(m.FSLayers) == 0 {
		return false, fmt.Errorf("no FSLayers in manifest for tag %q", tag)
	}
	keys, err := manifest.Verify(m)
	if err != nil {
		return false, fmt.Errorf("error verifying manifest for tag %q: %v", tag, err)
	}
	verified, err = p.verifyTrustedKeys(m.Name, keys)
	if err != nil {
		return false, fmt.Errorf("error verifying manifest keys: %v", err)
	}
	return verified, nil
}

func verifyManifest(signedManifest *schema1.SignedManifest, tag string) (m *schema1.Manifest, err error) {
	// If pull by digest, then verify the manifest digest. NOTE: It is
	// important to do this first, before any other content validation. If the
	// digest cannot be verified, don't even bother with those other things.
	if manifestDigest, err := digest.ParseDigest(tag); err == nil {
		verifier, err := digest.NewDigestVerifier(manifestDigest)
		if err != nil {
			return nil, err
		}
		payload, err := signedManifest.Payload()
		if err != nil {
			// If this failed, the signatures section was corrupted
			// or missing. Treat the entire manifest as the payload.
			payload = signedManifest.Raw
		}
		if _, err := verifier.Write(payload); err != nil {
			return nil, err
		}
		if !verifier.Verified() {
			err := fmt.Errorf("image verification failed for digest %s", manifestDigest)
			logrus.Error(err)
			return nil, err
		}

		var verifiedManifest schema1.Manifest
		if err = json.Unmarshal(payload, &verifiedManifest); err != nil {
			return nil, err
		}
		m = &verifiedManifest
	} else {
		m = &signedManifest.Manifest
	}

	if m.SchemaVersion != 1 {
		return nil, fmt.Errorf("unsupported schema version %d for tag %q", m.SchemaVersion, tag)
	}
	if len(m.FSLayers) != len(m.History) {
		return nil, fmt.Errorf("length of history not equal to number of layers for tag %q", tag)
	}
	if len(m.FSLayers) == 0 {
		return nil, fmt.Errorf("no FSLayers in manifest for tag %q", tag)
	}
	return m, nil
}

// ManifestMatchesImage returns true if the provided manifest matches the name of the image.
func ManifestMatchesImage(image *Image, newManifest []byte) (bool, error) {
	dgst, err := digest.ParseDigest(image.Name)
	if err != nil {
		return false, err
	}
	v, err := digest.NewDigestVerifier(dgst)
	if err != nil {
		return false, err
	}
	sm := schema1.SignedManifest{Raw: newManifest}
	raw, err := sm.Payload()
	if err != nil {
		return false, err
	}
	if _, err := v.Write(raw); err != nil {
		return false, err
	}
	return v.Verified(), nil
}

// ImageConfigMatchesImage returns true if the provided image config matches a digest
// stored in the manifest of the image.
func ImageConfigMatchesImage(image *Image, imageConfig []byte) (bool, error) {
	if image.DockerImageManifestMediaType != schema2.MediaTypeManifest {
		return false, nil
	}

	var m schema2.DeserializedManifest
	if err := json.Unmarshal([]byte(image.DockerImageManifest), &m); err != nil {
		return false, err
	}

	v, err := digest.NewDigestVerifier(m.Config.Digest)
	if err != nil {
		return false, err
	}

	if _, err := v.Write(imageConfig); err != nil {
		return false, err
	}

	return v.Verified(), nil
}

func (p *v2Puller) validateManifest(m *manifest.SignedManifest, tag string) (verified bool, err error) {
	// TODO(tiborvass): what's the usecase for having manifest == nil and err == nil ? Shouldn't be the error be "DoesNotExist" ?
	if m == nil {
		return false, fmt.Errorf("image manifest does not exist for tag %q", tag)
	}
	if m.SchemaVersion != 1 {
		return false, fmt.Errorf("unsupported schema version %d for tag %q", m.SchemaVersion, tag)
	}
	if len(m.FSLayers) != len(m.History) {
		return false, fmt.Errorf("length of history not equal to number of layers for tag %q", tag)
	}
	if len(m.FSLayers) == 0 {
		return false, fmt.Errorf("no FSLayers in manifest for tag %q", tag)
	}
	keys, err := manifest.Verify(m)
	if err != nil {
		return false, fmt.Errorf("error verifying manifest for tag %q: %v", tag, err)
	}
	verified, err = p.verifyTrustedKeys(m.Name, keys)
	if err != nil {
		return false, fmt.Errorf("error verifying manifest keys: %v", err)
	}
	localDigest, err := digest.ParseDigest(tag)
	// if pull by digest, then verify
	if err == nil {
		verifier, err := digest.NewDigestVerifier(localDigest)
		if err != nil {
			return false, err
		}
		payload, err := m.Payload()
		if err != nil {
			return false, err
		}
		if _, err := verifier.Write(payload); err != nil {
			return false, err
		}
		verified = verified && verifier.Verified()
	}
	return verified, nil
}

func TestSimpleRead(t *testing.T) {
	ctx := context.Background()
	content := make([]byte, 1<<20)
	n, err := mrand.Read(content)
	if err != nil {
		t.Fatalf("unexpected error building random data: %v", err)
	}

	if n != len(content) {
		t.Fatalf("random read didn't fill buffer")
	}

	dgst, err := digest.FromReader(bytes.NewReader(content))
	if err != nil {
		t.Fatalf("unexpected error digesting random content: %v", err)
	}

	driver := inmemory.New()
	path := "/random"

	if err := driver.PutContent(ctx, path, content); err != nil {
		t.Fatalf("error putting patterned content: %v", err)
	}

	fr, err := newFileReader(ctx, driver, path, int64(len(content)))
	if err != nil {
		t.Fatalf("error allocating file reader: %v", err)
	}

	verifier, err := digest.NewDigestVerifier(dgst)
	if err != nil {
		t.Fatalf("error getting digest verifier: %s", err)
	}

	io.Copy(verifier, fr)

	if !verifier.Verified() {
		t.Fatalf("unable to verify read data")
	}
}

// verifyDigest checks the contents of p against the provided digest. Note
// that for manifests, this is the signed payload and not the raw bytes with
// signatures.
func verifyDigest(dgst digest.Digest, p []byte) error {
	if err := dgst.Validate(); err != nil {
		return fmt.Errorf("error validating  digest %q: %v", dgst, err)
	}

	verifier, err := digest.NewDigestVerifier(dgst)
	if err != nil {
		// There are not many ways this can go wrong: if it does, its
		// fatal. Likley, the cause would be poor validation of the
		// incoming reference.
		return fmt.Errorf("error creating verifier for digest %q: %v", dgst, err)
	}

	if _, err := verifier.Write(p); err != nil {
		return fmt.Errorf("error writing payload to digest verifier (verifier target %q): %v", dgst, err)
	}

	if !verifier.Verified() {
		return fmt.Errorf("verification against digest %q failed", dgst)
	}

	return nil
}

func (p *v2Puller) pullSchema2ImageConfig(ctx context.Context, dgst digest.Digest) (configJSON []byte, err error) {
	blobs := p.repo.Blobs(ctx)
	configJSON, err = blobs.Get(ctx, dgst)
	if err != nil {
		return nil, err
	}

	// Verify image config digest
	verifier, err := digest.NewDigestVerifier(dgst)
	if err != nil {
		return nil, err
	}
	if _, err := verifier.Write(configJSON); err != nil {
		return nil, err
	}
	if !verifier.Verified() {
		err := fmt.Errorf("image config verification failed for digest %s", dgst)
		logrus.Error(err)
		return nil, err
	}

	return configJSON, nil
}

// 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.fileWriter.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.Size = 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.Size > 0 {
		if desc.Size != 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.Size = 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.Canonical == 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.Canonical.New()

			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.fileWriter.driver, bw.path, desc.Size)
			if err != nil {
				return distribution.Descriptor{}, err
			}
			defer fr.Close()

			tr := io.TeeReader(fr, digester.Hash())

			if _, err := io.Copy(digestVerifier, tr); err != nil {
//.........这里部分代码省略.........

// GetRemoteCA returns the remote endpoint's CA certificate
func GetRemoteCA(ctx context.Context, d digest.Digest, r remotes.Remotes) (RootCA, error) {
	// This TLS Config is intentionally using InsecureSkipVerify. Either we're
	// doing TOFU, in which case we don't validate the remote CA, or we're using
	// a user supplied hash to check the integrity of the CA certificate.
	insecureCreds := credentials.NewTLS(&tls.Config{InsecureSkipVerify: true})
	opts := []grpc.DialOption{
		grpc.WithTransportCredentials(insecureCreds),
		grpc.WithTimeout(5 * time.Second),
		grpc.WithBackoffMaxDelay(5 * time.Second),
	}

	peer, err := r.Select()
	if err != nil {
		return RootCA{}, err
	}

	conn, err := grpc.Dial(peer.Addr, opts...)
	if err != nil {
		return RootCA{}, err
	}
	defer conn.Close()

	client := api.NewCAClient(conn)
	ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
	defer cancel()
	defer func() {
		if err != nil {
			r.Observe(peer, -remotes.DefaultObservationWeight)
			return
		}
		r.Observe(peer, remotes.DefaultObservationWeight)
	}()
	response, err := client.GetRootCACertificate(ctx, &api.GetRootCACertificateRequest{})
	if err != nil {
		return RootCA{}, err
	}

	if d != "" {
		verifier, err := digest.NewDigestVerifier(d)
		if err != nil {
			return RootCA{}, errors.Wrap(err, "unexpected error getting digest verifier")
		}

		io.Copy(verifier, bytes.NewReader(response.Certificate))

		if !verifier.Verified() {
			return RootCA{}, errors.Errorf("remote CA does not match fingerprint. Expected: %s", d.Hex())

		}
	}

	// Check the validity of the remote Cert
	_, err = helpers.ParseCertificatePEM(response.Certificate)
	if err != nil {
		return RootCA{}, err
	}

	// Create a Pool with our RootCACertificate
	pool := x509.NewCertPool()
	if !pool.AppendCertsFromPEM(response.Certificate) {
		return RootCA{}, errors.New("failed to append certificate to cert pool")
	}

	return RootCA{Cert: response.Certificate, Digest: digest.FromBytes(response.Certificate), Pool: pool}, nil
}

func (p *v2Puller) download(di *downloadInfo) {
	logrus.Debugf("pulling blob %q to %s", di.digest, di.img.ID)

	out := p.config.OutStream

	if c, err := p.poolAdd("pull", "img:"+di.img.ID); err != nil {
		if c != nil {
			out.Write(p.sf.FormatProgress(stringid.TruncateID(di.img.ID), "Layer already being pulled by another client. Waiting.", nil))
			<-c
			out.Write(p.sf.FormatProgress(stringid.TruncateID(di.img.ID), "Download complete", nil))
		} else {
			logrus.Debugf("Image (id: %s) pull is already running, skipping: %v", di.img.ID, err)
		}
		di.err <- nil
		return
	}

	defer p.poolRemove("pull", "img:"+di.img.ID)
	tmpFile, err := ioutil.TempFile("", "GetImageBlob")
	if err != nil {
		di.err <- err
		return
	}

	blobs := p.repo.Blobs(nil)

	desc, err := blobs.Stat(nil, di.digest)
	if err != nil {
		logrus.Debugf("Error statting layer: %v", err)
		di.err <- err
		return
	}
	di.size = desc.Size

	layerDownload, err := blobs.Open(nil, di.digest)
	if err != nil {
		logrus.Debugf("Error fetching layer: %v", err)
		di.err <- err
		return
	}
	defer layerDownload.Close()

	verifier, err := digest.NewDigestVerifier(di.digest)
	if err != nil {
		di.err <- err
		return
	}

	reader := progressreader.New(progressreader.Config{
		In:        ioutil.NopCloser(io.TeeReader(layerDownload, verifier)),
		Out:       out,
		Formatter: p.sf,
		Size:      int(di.size),
		NewLines:  false,
		ID:        stringid.TruncateID(di.img.ID),
		Action:    "Downloading",
	})
	io.Copy(tmpFile, reader)

	out.Write(p.sf.FormatProgress(stringid.TruncateID(di.img.ID), "Verifying Checksum", nil))

	if !verifier.Verified() {
		err = fmt.Errorf("filesystem layer verification failed for digest %s", di.digest)
		logrus.Error(err)
		di.err <- err
		return
	}

	out.Write(p.sf.FormatProgress(stringid.TruncateID(di.img.ID), "Download complete", nil))

	logrus.Debugf("Downloaded %s to tempfile %s", di.img.ID, tmpFile.Name())
	di.tmpFile = tmpFile
	di.layer = layerDownload

	di.err <- nil
}