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.


NGX_MAKEFILE=$NGX_OBJS/Makefile
NGX_MODULES_C=$NGX_OBJS/ngx_modules.c

NGX_AUTO_HEADERS_H=$NGX_OBJS/ngx_auto_headers.h
NGX_AUTO_CONFIG_H=$NGX_OBJS/ngx_auto_config.h

NGX_AUTOTEST=$NGX_OBJS/autotest
NGX_AUTOCONF_ERR=$NGX_OBJS/autoconf.err

# STUBs
NGX_ERR=$NGX_OBJS/autoconf.err
MAKEFILE=$NGX_OBJS/Makefile


NGX_PCH=
NGX_USE_PCH=


# check the echo's "-n" option and "\c" capability

if echo "test\c" | grep c >/dev/null; then

    if echo -n test | grep n >/dev/null; then
        ngx_n=
        ngx_c=

    else
        ngx_n=-n
        ngx_c=
    fi

else
    ngx_n=
    ngx_c='\c'
fi


# create Makefile

cat << END > Makefile

default:	build

clean:
	rm -rf Makefile $NGX_OBJS

.PHONY:	default clean
END