Method getBlob

docker/docker_client.go:1037–1073

getBlob returns a stream for the specified blob in ref, and the blob’s size (or -1 if unknown). The Digest field in BlobInfo is guaranteed to be provided, Size may be -1 and MediaType may be optionally provided. May update BlobInfoCache, preferably after it knows for certain that a blob truly exists

(ctx context.Context, ref dockerReference, info types.BlobInfo, cache types.BlobInfoCache)

// The Digest field in BlobInfo is guaranteed to be provided, Size may be -1 and MediaType may be optionally provided.
// May update BlobInfoCache, preferably after it knows for certain that a blob truly exists at a specific location.
func (c *dockerClient) getBlob(ctx context.Context, ref dockerReference, info types.BlobInfo, cache types.BlobInfoCache) (io.ReadCloser, int64, error) {
	if len(info.URLs) != 0 {
		r, s, err := c.getExternalBlob(ctx, info.URLs)
		if err != nil {
			return nil, 0, err
		} else if r != nil {
			return r, s, nil
		}
	}

	if err := info.Digest.Validate(); err != nil { // Make sure info.Digest.String() does not contain any unexpected characters
		return nil, 0, err
	}
	path := fmt.Sprintf(blobsPath, reference.Path(ref.ref), info.Digest.String())
	logrus.Debugf("Downloading %s", path)
	res, err := c.makeRequest(ctx, http.MethodGet, path, nil, nil, v2Auth, nil)
	if err != nil {
		return nil, 0, err
	}
	if res.StatusCode != http.StatusOK {
		err := registryHTTPResponseToError(res)
		res.Body.Close()
		return nil, 0, fmt.Errorf("fetching blob: %w", err)
	}
	cache.RecordKnownLocation(ref.Transport(), bicTransportScope(ref), info.Digest, newBICLocationReference(ref))
	blobSize, err := getBlobSize(res)
	if err != nil {
		blobSize = -1
	}

	reconnectingReader, err := newBodyReader(ctx, c, path, res.Body)
	if err != nil {
		res.Body.Close()
		return nil, 0, err
	}
	return reconnectingReader, blobSize, nil
}

// getOCIDescriptorContents returns the contents a blob specified by descriptor in ref, which must fit within limit.
func (c *dockerClient) getOCIDescriptorContents(ctx context.Context, ref dockerReference, desc imgspecv1.Descriptor, maxSize int, cache types.BlobInfoCache) ([]byte, error) {