code: protected Buffer getBuffer(Dsn dsn) {
          String bufferDir = Lookup.lookup(BUFFER_DIR_OPTION, dsn);
          if (bufferDir != null) {
              return new DiskBuffer(new File(bufferDir), getBufferSize(dsn));
          }
          return null;
      }
docs: Get the {@link Buffer} where events are stored when network is down.
  
  @param dsn Dsn passed in by the user.
  @return the {@link Buffer} where events are stored when network is down.