@Override
      public void write(OutputStream os) throws IOException {
        ByteStreams.copy(is, os);
      }
Creates a writer callback that copies all the content read from an {@link InputStream} into the
target stream.

<p>This writer can be used only once.

@param is the source
@return the writer callback
imagepipeline-base/src/main/java/com/facebook/cache/common/WriterCallbacks.java