QUIC: ignore duplicate PATH_CHALLENGE frames. According to RFC 9000, an endpoint SHOULD NOT send multiple PATH_CHALLENGE frames in a single packet. The change adds a check to enforce this claim to optimize server behavior. Previously each PATH_CHALLENGE always resulted in a single response datagram being sent to client. The effect of this was however limited by QUIC flood protection. Also, PATH_CHALLENGE is explicitly disabled in Initial and Handshake levels, see RFC 9000, Table 3. However, technically it may be sent by client in 0-RTT over a new path without actual migration, even though the migration itself is prohibited during handshake. This allows client to coalesce multiple 0-RTT packets each carrying a PATH_CHALLENGE and end up with multiple PATH_CHALLENGEs per datagram. This again leads to suboptimal behavior, see above. Since the purpose of sending PATH_CHALLENGE frames in 0-RTT is unclear, these frames are now only allowed in 1-RTT. For 0-RTT they are silently ignored.

# Copyright (C) Igor Sysoev
# Copyright (C) Nginx, Inc.


if [ $USE_PCRE = YES -o $PCRE != NONE ]; then
    . auto/lib/pcre/conf

else
    if [ $USE_PCRE = DISABLED -a $HTTP = YES -a $HTTP_REWRITE = YES ]; then

cat << END

$0: error: the HTTP rewrite module requires the PCRE library.
You can either disable the module by using --without-http_rewrite_module
option or you have to enable the PCRE support.

END
        exit 1
    fi
fi


if [ $USE_OPENSSL = YES ]; then
    . auto/lib/openssl/conf
fi

if [ $USE_ZLIB = YES ]; then
    . auto/lib/zlib/conf
fi

if [ $USE_LIBXSLT != NO ]; then
    . auto/lib/libxslt/conf
fi

if [ $USE_LIBGD != NO ]; then
    . auto/lib/libgd/conf
fi

if [ $USE_PERL != NO ]; then
    . auto/lib/perl/conf
fi

if [ $USE_GEOIP != NO ]; then
    . auto/lib/geoip/conf
fi

if [ $NGX_GOOGLE_PERFTOOLS = YES ]; then
    . auto/lib/google-perftools/conf
fi

if [ $NGX_LIBATOMIC != NO ]; then
    . auto/lib/libatomic/conf
fi