@Override
    public void reset() throws IOException {
        if (!in.markSupported()) {
            throw new IOException("Mark not supported");
        }
        if (mark == -1) {
            throw new IOException("Mark not set");
        }

        in.reset();
        firstOffsetInLastRead = mark;
    }
Creates a <code>FilterInputStream</code>
by assigning the  argument <code>in</code>
to the field <code>this.in</code> so as
to remember it for later use.

@param in the underlying input stream, or <code>null</code> if
          this instance is to be created without an underlying stream.
stroom-data/stroom-data-store-impl/src/main/java/stroom/data/store/impl/LocationAwareInputStream.java