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.
 */


#ifndef _NGX_PARSE_TIME_H_INCLUDED_
#define _NGX_PARSE_TIME_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


time_t ngx_parse_http_time(u_char *value, size_t len);

/* compatibility */
#define ngx_http_parse_time(value, len)  ngx_parse_http_time(value, len)


#endif /* _NGX_PARSE_TIME_H_INCLUDED_ */