Blob fetch should not attempt range request by default

[shizhMSFT]

oras-go always attempts Range header to seekable http client, which is aggressive.

oras-go/registry/remote/repository.go

Lines 616 to 657 in 511e4d4

	func (s *blobStore) Fetch(ctx context.Context, target ocispec.Descriptor) (rc io.ReadCloser, err error) {
	ref := s.repo.Reference
	ref.Reference = target.Digest.String()
	ctx = registryutil.WithScopeHint(ctx, ref, auth.ActionPull)
	url := buildRepositoryBlobURL(s.repo.PlainHTTP, ref)
	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
	if err != nil {
	return nil, err
	}
	// probe server range request ability.
	// Docker spec allows range header form of "Range: bytes=<start>-<end>".
	// However, the remote server may still not RFC 7233 compliant.
	// Reference: https://docs.docker.com/registry/spec/api/#blob
	if target.Size > 0 {
	req.Header.Set("Range", fmt.Sprintf("bytes=0-%d", target.Size-1))
	}
	resp, err := s.repo.client().Do(req)
	if err != nil {
	return nil, err
	}
	defer func() {
	if err != nil {
	resp.Body.Close()
	}
	}()
	switch resp.StatusCode {
	case http.StatusOK: // server does not support seek as `Range` was ignored.
	if size := resp.ContentLength; size != -1 && size != target.Size {
	return nil, fmt.Errorf("%s %q: mismatch Content-Length", resp.Request.Method, resp.Request.URL)
	}
	return resp.Body, nil
	case http.StatusPartialContent:
	return httputil.NewReadSeekCloser(s.repo.client(), req, resp.Body, target.Size), nil
	case http.StatusNotFound:
	return nil, fmt.Errorf("%s: %w", target.Digest, errdef.ErrNotFound)
	default:
	return nil, errutil.ParseErrorResponse(resp)
	}
	}

The Docker spec states that

This endpoint may also support RFC7233 compliant range requests. Support can be detected by issuing a HEAD request. If the header Accept-Range: bytes is returned, range requests can be used to fetch partial content.

Therefore, oras-go should do normal request by default and attempt range request only if the server explicitly states it support range query in order to be compatible with most registries with best effort.

Known impacted registry provider:

• jFrog Artifactory