Added warning about redefinition of listen socket protocol options. The "listen" directive in the http module can be used multiple times in different server blocks. Originally, it was supposed to be specified once with various socket options, and without any parameters in virtual server blocks. For example: server { listen 80 backlog=1024; server_name foo; ... } server { listen 80; server_name bar; ... } server { listen 80; server_name bazz; ... } The address part of the syntax ("address[:port]" / "port" / "unix:path") uniquely identifies the listening socket, and therefore is enough for name-based virtual servers (to let nginx know that the virtual server accepts requests on the listening socket in question). To ensure that listening options do not conflict between virtual servers, they were allowed only once. For example, the following configuration will be rejected ("duplicate listen options for 0.0.0.0:80 in ..."): server { listen 80 backlog=1024; server_name foo; ... } server { listen 80 backlog=512; server_name bar; ... } At some point it was, however, noticed, that it is sometimes convenient to repeat some options for clarity. In nginx 0.8.51 the "ssl" parameter was allowed to be specified multiple times, e.g.: server { listen 443 ssl backlog=1024; server_name foo; ... } server { listen 443 ssl; server_name bar; ... } server { listen 443 ssl; server_name bazz; ... } This approach makes configuration more readable, since SSL sockets are immediately visible in the configuration. If this is not needed, just the address can still be used. Later, additional protocol-specific options similar to "ssl" were introduced, notably "http2" and "proxy_protocol". With these options, one can write: server { listen 443 ssl backlog=1024; server_name foo; ... } server { listen 443 http2; server_name bar; ... } server { listen 443 proxy_protocol; server_name bazz; ... } The resulting socket will use ssl, http2, and proxy_protocol, but this is not really obvious from the configuration. To emphasize such misleading configurations are discouraged, nginx now warns as long as the "listen" directive is used with options different from the options previously used if this is potentially confusing. In particular, the following configurations are allowed: server { listen 8401 ssl backlog=1024; server_name foo; } server { listen 8401 ssl; server_name bar; } server { listen 8401 ssl; server_name bazz; } server { listen 8402 ssl http2 backlog=1024; server_name foo; } server { listen 8402 ssl; server_name bar; } server { listen 8402 ssl; server_name bazz; } server { listen 8403 ssl; server_name bar; } server { listen 8403 ssl; server_name bazz; } server { listen 8403 ssl http2; server_name foo; } server { listen 8404 ssl http2 backlog=1024; server_name foo; } server { listen 8404 http2; server_name bar; } server { listen 8404 http2; server_name bazz; } server { listen 8405 ssl http2 backlog=1024; server_name foo; } server { listen 8405 ssl http2; server_name bar; } server { listen 8405 ssl http2; server_name bazz; } server { listen 8406 ssl; server_name foo; } server { listen 8406; server_name bar; } server { listen 8406; server_name bazz; } And the following configurations will generate warnings: server { listen 8501 ssl http2 backlog=1024; server_name foo; } server { listen 8501 http2; server_name bar; } server { listen 8501 ssl; server_name bazz; } server { listen 8502 backlog=1024; server_name foo; } server { listen 8502 ssl; server_name bar; } server { listen 8503 ssl; server_name foo; } server { listen 8503 http2; server_name bar; } server { listen 8504 ssl; server_name foo; } server { listen 8504 http2; server_name bar; } server { listen 8504 proxy_protocol; server_name bazz; } server { listen 8505 ssl http2 proxy_protocol; server_name foo; } server { listen 8505 ssl http2; server_name bar; } server { listen 8505 ssl; server_name bazz; } server { listen 8506 ssl http2; server_name foo; } server { listen 8506 ssl; server_name bar; } server { listen 8506; server_name bazz; } server { listen 8507 ssl; server_name bar; } server { listen 8507; server_name bazz; } server { listen 8507 ssl http2; server_name foo; } server { listen 8508 ssl; server_name bar; } server { listen 8508; server_name bazz; } server { listen 8508 ssl backlog=1024; server_name foo; } server { listen 8509; server_name bazz; } server { listen 8509 ssl; server_name bar; } server { listen 8509 ssl backlog=1024; server_name foo; } The basic idea is that at most two sets of protocol options are allowed: the main one (with socket options, if any), and a shorter one, with options being a subset of the main options, repeated for clarity. As long as the shorter set of protocol options is used, all listen directives except the main one should use it.

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


#ifndef _NGX_CORE_H_INCLUDED_
#define _NGX_CORE_H_INCLUDED_


#include <ngx_config.h>


typedef struct ngx_module_s          ngx_module_t;
typedef struct ngx_conf_s            ngx_conf_t;
typedef struct ngx_cycle_s           ngx_cycle_t;
typedef struct ngx_pool_s            ngx_pool_t;
typedef struct ngx_chain_s           ngx_chain_t;
typedef struct ngx_log_s             ngx_log_t;
typedef struct ngx_open_file_s       ngx_open_file_t;
typedef struct ngx_command_s         ngx_command_t;
typedef struct ngx_file_s            ngx_file_t;
typedef struct ngx_event_s           ngx_event_t;
typedef struct ngx_event_aio_s       ngx_event_aio_t;
typedef struct ngx_connection_s      ngx_connection_t;
typedef struct ngx_thread_task_s     ngx_thread_task_t;
typedef struct ngx_ssl_s             ngx_ssl_t;
typedef struct ngx_proxy_protocol_s  ngx_proxy_protocol_t;
typedef struct ngx_ssl_connection_s  ngx_ssl_connection_t;
typedef struct ngx_udp_connection_s  ngx_udp_connection_t;

typedef void (*ngx_event_handler_pt)(ngx_event_t *ev);
typedef void (*ngx_connection_handler_pt)(ngx_connection_t *c);


#define  NGX_OK          0
#define  NGX_ERROR      -1
#define  NGX_AGAIN      -2
#define  NGX_BUSY       -3
#define  NGX_DONE       -4
#define  NGX_DECLINED   -5
#define  NGX_ABORT      -6


#include <ngx_errno.h>
#include <ngx_atomic.h>
#include <ngx_thread.h>
#include <ngx_rbtree.h>
#include <ngx_time.h>
#include <ngx_socket.h>
#include <ngx_string.h>
#include <ngx_files.h>
#include <ngx_shmem.h>
#include <ngx_process.h>
#include <ngx_user.h>
#include <ngx_dlopen.h>
#include <ngx_parse.h>
#include <ngx_parse_time.h>
#include <ngx_log.h>
#include <ngx_alloc.h>
#include <ngx_palloc.h>
#include <ngx_buf.h>
#include <ngx_queue.h>
#include <ngx_array.h>
#include <ngx_list.h>
#include <ngx_hash.h>
#include <ngx_file.h>
#include <ngx_crc.h>
#include <ngx_crc32.h>
#include <ngx_murmurhash.h>
#if (NGX_PCRE)
#include <ngx_regex.h>
#endif
#include <ngx_radix_tree.h>
#include <ngx_times.h>
#include <ngx_rwlock.h>
#include <ngx_shmtx.h>
#include <ngx_slab.h>
#include <ngx_inet.h>
#include <ngx_cycle.h>
#include <ngx_resolver.h>
#if (NGX_OPENSSL)
#include <ngx_event_openssl.h>
#endif
#include <ngx_process_cycle.h>
#include <ngx_conf_file.h>
#include <ngx_module.h>
#include <ngx_open_file_cache.h>
#include <ngx_os.h>
#include <ngx_connection.h>
#include <ngx_syslog.h>
#include <ngx_proxy_protocol.h>


#define LF     (u_char) '\n'
#define CR     (u_char) '\r'
#define CRLF   "\r\n"


#define ngx_abs(value)       (((value) >= 0) ? (value) : - (value))
#define ngx_max(val1, val2)  ((val1 < val2) ? (val2) : (val1))
#define ngx_min(val1, val2)  ((val1 > val2) ? (val2) : (val1))

void ngx_cpuinfo(void);

#if (NGX_HAVE_OPENAT)
#define NGX_DISABLE_SYMLINKS_OFF        0
#define NGX_DISABLE_SYMLINKS_ON         1
#define NGX_DISABLE_SYMLINKS_NOTOWNER   2
#endif

#endif /* _NGX_CORE_H_INCLUDED_ */