Cleanup libz stream memory when gzip fails

[dkalinowski]

🛠 Summary

Coverity
CVS-157750

full code of the method

/* Compress gzip data */
std::string gzipCompress(const char *data, const size_t ndata)
{
    z_stream strm = {nullptr,
                     0,
                     0,
                     nullptr,
                     0,
                     0,
                     nullptr,
                     nullptr,
                     nullptr,
                     nullptr,
                     nullptr,
                     0,
                     0,
                     0};
    if (data && ndata > 0)
    {
        if (deflateInit2(&strm,
                         Z_DEFAULT_COMPRESSION,
                         Z_DEFLATED,
                         MAX_WBITS + 16,
                         8,
                         Z_DEFAULT_STRATEGY) != Z_OK)
        {
            LOG_ERROR << "deflateInit2 error!";
            (void)deflateEnd(&strm);
            return std::string{};
        }
        std::string outstr;
        outstr.resize(compressBound(static_cast<uLong>(ndata)));
        strm.next_in = (Bytef *)data;
        strm.avail_in = static_cast<uInt>(ndata);
        int ret;
        do
        {
            if (strm.total_out >= outstr.size())
            {
                outstr.resize(strm.total_out * 2);
            }
            assert(outstr.size() >= strm.total_out);
            strm.avail_out = static_cast<uInt>(outstr.size() - strm.total_out);
            strm.next_out = (Bytef *)outstr.data() + strm.total_out;
            ret = deflate(&strm, Z_FINISH); /* no bad return value */
            if (ret == Z_STREAM_ERROR)
            {
                (void)deflateEnd(&strm);
                return std::string{};
            }
        } while (strm.avail_out == 0);
        assert(strm.avail_in == 0);
        assert(ret == Z_STREAM_END); /* stream will be complete */
        outstr.resize(strm.total_out);
        /* clean up and return */
        (void)deflateEnd(&strm);
        return outstr;
    }
    return std::string{};
}

🧪 Checklist

• Change follows security best practices.