blobstore/read.go
func (r *reader) fetch(off int64) error {
	req := &blobpb.FetchDataRequest{
		BlobKey:    proto.String(string(r.blobKey)),
		StartIndex: proto.Int64(off),
		EndIndex:   proto.Int64(off + readBufferSize - 1), // EndIndex is inclusive.
	}
	res := &blobpb.FetchDataResponse{}
	if err := internal.Call(r.c, "blobstore", "FetchData", req, res); err != nil {
		return err
	}
	if len(res.Data) == 0 {
		return io.EOF
	}
	r.buf, r.r, r.off = res.Data, 0, off
	return nil
}
func (r *reader) fetch(off int64) error {
	req := &blobpb.FetchDataRequest{
		BlobKey:    proto.String(string(r.blobKey)),
		StartIndex: proto.Int64(off),
		EndIndex:   proto.Int64(off + readBufferSize - 1), // EndIndex is inclusive.
	}
	res := &blobpb.FetchDataResponse{}
	if err := internal.Call(r.c, "blobstore", "FetchData", req, res); err != nil {
		return err
	}
	if len(res.Data) == 0 {
		return io.EOF
	}
	r.buf, r.r, r.off = res.Data, 0, off
	return nil
}
// fetch fetches readBufferSize bytes starting at the given offset. On success,
// the data is saved as r.buf.