BlobBuilder builder = blobBuilders.get();
builder.name(key);
File file = getFileForBlobKey(container, key);
ByteSource byteSource = Files.asByteSource(file);
try {
builder.payload(byteSource)
.contentLength(byteSource.size())
.contentMD5(byteSource.hash(Hashing.md5()).asBytes());
} catch (IOException e) {
logger.error("An error occurred calculating MD5 for blob %s from container ", key, container);
Throwables.propagateIfPossible(e);