private void preParse(FetchEmitTuple t, InputStream stream, Metadata metadata,
                          ParseContext parseContext) {
        TemporaryResources tmp = null;
        try {
            TikaInputStream tis = TikaInputStream.cast(stream);
            if (tis == null) {
                tis = TikaInputStream.get(stream, tmp, metadata);
            }
            _preParse(t, tis, metadata, parseContext);
        } finally {
            IOUtils.closeQuietly(tmp);
        }
        //do we want to filter the metadata to digest, length, content-type?
        writeIntermediate(t.getEmitKey(), metadata);
    }
returns stack trace if there was a container exception or empty string
if there was no stacktrace

@param t
@param metadataList
@return
tika-core/src/main/java/org/apache/tika/pipes/PipesServer.java