Lingering close for connections with pipelined requests. This is expected to help with clients using pipelining with some constant depth, such as apt[1][2]. When downloading many resources, apt uses pipelining with some constant depth, a number of requests in flight. This essentially means that after receiving a response it sends an additional request to the server, and this can result in requests arriving to the server at any time. Further, additional requests are sent one-by-one, and can be easily seen as such (neither as pipelined, nor followed by pipelined requests). The only safe approach to close such connections (for example, when keepalive_requests is reached) is with lingering. To do so, now nginx monitors if pipelining was used on the connection, and if it was, closes the connection with lingering. [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=973861#10 [2] https://mailman.nginx.org/pipermail/nginx-devel/2023-January/ZA2SP5SJU55LHEBCJMFDB2AZVELRLTHI.html

/*
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_SYSLOG_H_INCLUDED_
#define _NGX_SYSLOG_H_INCLUDED_


typedef struct {
    ngx_uint_t        facility;
    ngx_uint_t        severity;
    ngx_str_t         tag;

    ngx_addr_t        server;
    ngx_connection_t  conn;
    unsigned          busy:1;
    unsigned          nohostname:1;
} ngx_syslog_peer_t;


char *ngx_syslog_process_conf(ngx_conf_t *cf, ngx_syslog_peer_t *peer);
u_char *ngx_syslog_add_header(ngx_syslog_peer_t *peer, u_char *buf);
void ngx_syslog_writer(ngx_log_t *log, ngx_uint_t level, u_char *buf,
    size_t len);
ssize_t ngx_syslog_send(ngx_syslog_peer_t *peer, u_char *buf, size_t len);


#endif /* _NGX_SYSLOG_H_INCLUDED_ */