@Override
  public long getSize() {
    onEventComplete(Event.GetSize);
    return size;
  }
Constructs a {@link ReadableStreamChannel} whose read operations return data from the provided {@code buffer}.
@param buffer the {@link ByteBuffer} that is used to retrieve data from on invocation of read operations.
ambry-test-utils/src/main/java/com/github/ambry/router/ByteBufferRSC.java