1 Background
http://nginx.org/en/docs/http/ngx_http_stub_status_module.html
ngx_http_stub_status_module 是一个 Nginx 的内置 HTTP 模块，该模块可以提供 Nginx 的状态信息。默认情况下这个模块是不被编译进来的，所以在编译 Nginx 时要指定加载该模块：
--with-http_stub_status_module
为什么拿它做例子？因为它也是个足够短小精悍的模块，是一个典型 handler 模块。那么以后我们讲解模块的过程，都是：
- 简要的介绍
- 使用的实例
- 指令介绍
- 源码分析
2 Simple example
location /nginx_status { stub_status on; access_log off; access_log /usr/local/nginx/logs/status.log; #日志 allow SOME.IP.ADD.RESS; deny all;} 我们假设你是在本机上实验，并且开启的是 80 端口，那么在浏览器中输入：
http://localhost/nginx_status
会看到这样的信息：
Active connections: 291server accepts handled requests 16630948 16630948 31070465Reading: 6 Writing: 179 Waiting: 106
其含义很容易理解：
- 第一行
- 当前的活跃连接数：291
- 第二行
- 服务器已接受的连接数：16630948（accepted connection #）
- 服务器已处理的连接数：16630948（handled connection #）
- 服务器已处理的请求：31070465（可以算出，平均每个连接有 1.8 个请求）（handled connection #）
- 第三行
- Reading – Nginx 读取的请求头次数为 6；
- Writting – Nginx 读取请求体、处理请求并发送响应给客户端的次数为 179；
- Waiting – 当前活动的长连接数：106。
Nginx 官方的解释如下：
active connections– number of all open connectionsserver accepts handled requests– nginx accepted 16630948 connections, handled 16630948 connections (no one was closed just it was accepted), and handles 31070465 requests (1.8 requests per connection)reading– nginx reads request headerwriting– nginx reads request body, processes request, or writes response to a clientwaiting– keep-alive connections, actually it is active - (reading + writing)
3 Directives
这个模块中的唯一一个指令，是：
stub_status
- 语法：
stub_status on - 作用域：location
- 功能：统计这个 location 的信息。
4 Source analysis
先看完整代码：
/* * Copyright (C) Igor Sysoev * Copyright (C) Nginx, Inc. */#include#include #include static char *ngx_http_set_status(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);static ngx_command_t ngx_http_status_commands[] = { { ngx_string("stub_status"), NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG, ngx_http_set_status, 0, 0, NULL }, ngx_null_command};static ngx_http_module_t ngx_http_stub_status_module_ctx = { NULL, /* preconfiguration */ NULL, /* postconfiguration */ NULL, /* create main configuration */ NULL, /* init main configuration */ NULL, /* create server configuration */ NULL, /* merge server configuration */ NULL, /* create location configuration */ NULL /* merge location configuration */};ngx_module_t ngx_http_stub_status_module = { NGX_MODULE_V1, &ngx_http_stub_status_module_ctx, /* module context */ ngx_http_status_commands, /* module directives */ NGX_HTTP_MODULE, /* module type */ NULL, /* init master */ NULL, /* init module */ NULL, /* init process */ NULL, /* init thread */ NULL, /* exit thread */ NULL, /* exit process */ NULL, /* exit master */ NGX_MODULE_V1_PADDING};static ngx_int_t ngx_http_status_handler(ngx_http_request_t *r){ size_t size; ngx_int_t rc; ngx_buf_t *b; ngx_chain_t out; ngx_atomic_int_t ap, hn, ac, rq, rd, wr; if (r->method != NGX_HTTP_GET && r->method != NGX_HTTP_HEAD) { return NGX_HTTP_NOT_ALLOWED; } rc = ngx_http_discard_request_body(r); if (rc != NGX_OK) { return rc; } ngx_str_set(&r->headers_out.content_type, "text/plain"); if (r->method == NGX_HTTP_HEAD) { r->headers_out.status = NGX_HTTP_OK; rc = ngx_http_send_header(r); if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) { return rc; } } size = sizeof("Active connections: \n") + NGX_ATOMIC_T_LEN + sizeof("server accepts handled requests\n") - 1 + 6 + 3 * NGX_ATOMIC_T_LEN + sizeof("Reading: Writing: Waiting: \n") + 3 * NGX_ATOMIC_T_LEN; b = ngx_create_temp_buf(r->pool, size); if (b == NULL) { return NGX_HTTP_INTERNAL_SERVER_ERROR; } out.buf = b; out.next = NULL; ap = *ngx_stat_accepted; hn = *ngx_stat_handled; ac = *ngx_stat_active; rq = *ngx_stat_requests; rd = *ngx_stat_reading; wr = *ngx_stat_writing; b->last = ngx_sprintf(b->last, "Active connections: %uA \n", ac); b->last = ngx_cpymem(b->last, "server accepts handled requests\n", sizeof("server accepts handled requests\n") - 1); b->last = ngx_sprintf(b->last, " %uA %uA %uA \n", ap, hn, rq); b->last = ngx_sprintf(b->last, "Reading: %uA Writing: %uA Waiting: %uA \n", rd, wr, ac - (rd + wr)); r->headers_out.status = NGX_HTTP_OK; r->headers_out.content_length_n = b->last - b->pos; b->last_buf = 1; rc = ngx_http_send_header(r); if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) { return rc; } return ngx_http_output_filter(r, &out);}static char *ngx_http_set_status(ngx_conf_t *cf, ngx_command_t *cmd, void *conf){ ngx_http_core_loc_conf_t *clcf; clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module); clcf->handler = ngx_http_status_handler; return NGX_CONF_OK;}
的确够短小精悍吧？关键在于 Nginx 提供的模块扩展方式比较好，让你可以少写一些代码（NDK 可以让你写的更少，这是后话）。
4.1 模块定义 ngx_http_stub_status_module
ngx_module_t ngx_http_stub_status_module = { NGX_MODULE_V1, &ngx_http_stub_status_module_ctx, /* module context */ ngx_http_status_commands, /* module directives */ NGX_HTTP_MODULE, /* module type */ NULL, /* init master */ NULL, /* init module */ NULL, /* init process */ NULL, /* init thread */ NULL, /* exit thread */ NULL, /* exit process */ NULL, /* exit master */ NGX_MODULE_V1_PADDING}; 与此前介绍的 ngx_http_hello_world_module 并无本质区别。
4.2 命令集定义 ngx_http_status_commands
static ngx_command_t ngx_http_status_commands[] = { { ngx_string("stub_status"), NGX_HTTP_SRV_CONF|NGX_HTTP_LOC_CONF|NGX_CONF_FLAG, ngx_http_set_status, 0, 0, NULL }, ngx_null_command}; 命令集定义如上，得到如下信息：
- name：stub_status
- type：server conf、location conf、conf flag，其中最后一个比较陌生，相似的取值有：
#define NGX_CONF_ARGS_NUMBER 0x000000ff#define NGX_CONF_BLOCK 0x00000100#define NGX_CONF_FLAG 0x00000200#define NGX_CONF_ANY 0x00000400#define NGX_CONF_1MORE 0x00000800#define NGX_CONF_2MORE 0x00001000#define NGX_CONF_MULTI 0x00002000
- set：ngx_http_set_status
下面解释下一些 types：
4.2.1 NGX_CONF_XXX
以下宏定义来自 ngx_conf_file.h：
#define NGX_CONF_NOARGS 0x00000001 // 命令不接受参数#define NGX_CONF_TAKE1 0x00000002 // 命令携带1个参数#define NGX_CONF_TAKE2 0x00000004 // 命令携带2个参数#define NGX_CONF_TAKE3 0x00000008 // 命令携带3个参数#define NGX_CONF_TAKE4 0x00000010 // 命令携带4个参数#define NGX_CONF_TAKE5 0x00000020 // 命令携带5个参数#define NGX_CONF_TAKE6 0x00000040 // 命令携带6个参数#define NGX_CONF_TAKE7 0x00000080 // 命令携带7个参数#define NGX_CONF_TAKE12 (NGX_CONF_TAKE1|NGX_CONF_TAKE2) // 命令携带1个或2个参数#define NGX_CONF_TAKE13 (NGX_CONF_TAKE1|NGX_CONF_TAKE3) // 命令携带1个或3个参数#define NGX_CONF_TAKE23 (NGX_CONF_TAKE2|NGX_CONF_TAKE3) // 命令携带2个或3个参数#define NGX_CONF_TAKE123 (NGX_CONF_TAKE1|NGX_CONF_TAKE2|NGX_CONF_TAKE3) // 命令携带1个、2个或3个参数#define NGX_CONF_TAKE1234 (NGX_CONF_TAKE1|NGX_CONF_TAKE2|NGX_CONF_TAKE3|NGX_CONF_TAKE4) // 命令携带1个、2个、3个或4个参数#define NGX_CONF_ARGS_NUMBER 0x000000ff // 命令#define NGX_CONF_BLOCK 0x00000100 // 块域，后面跟 {…}，比如 server {...}#define NGX_CONF_FLAG 0x00000200 // 命令接受“on|off”参数#define NGX_CONF_ANY 0x00000400#define NGX_CONF_1MORE 0x00000800 // 命令携带至少1个参数#define NGX_CONF_2MORE 0x00001000 // 命令携带至少2个参数#define NGX_CONF_MULTI 0x00002000 // 命令携带多个参数 4.3 上下文定义 ngx_http_stub_status_module_ctx
static ngx_http_module_t ngx_http_stub_status_module_ctx = { NULL, /* preconfiguration */ NULL, /* postconfiguration */ NULL, /* create main configuration */ NULL, /* init main configuration */ NULL, /* create server configuration */ NULL, /* merge server configuration */ NULL, /* create location configuration */ NULL /* merge location configuration */}; 这个都是 NULL，够简单，无话可说了⋯⋯
4.4 命令设置函数 ngx_http_set_status
static char *ngx_http_set_status(ngx_conf_t *cf, ngx_command_t *cmd, void *conf) { ngx_http_core_loc_conf_t *clcf; clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module); clcf->handler = ngx_http_status_handler; return NGX_CONF_OK;} 和 ngx_http_hello_world_module 对比下：
static char* ngx_http_hello_world(ngx_conf_t* cf, ngx_command_t* cmd, void* conf) { ngx_http_core_loc_conf_t* clcf; clcf = ngx_http_conf_get_module_loc_conf(cf, ngx_http_core_module); clcf->handler = ngx_http_hello_world_handler; ngx_conf_set_str_slot(cf, cmd, conf); return NGX_CONF_OK;} 唯一的区别，就是 ngx_http_hello_world_module 多了一句 ngx_conf_set_str_slot。这个先留做一个问题，后面会介绍，暂时与关键主题无关。
4.5 命令处理函数 ngx_http_status_handler
static ngx_int_t ngx_http_status_handler(ngx_http_request_t *r){ size_t size; ngx_int_t rc; ngx_buf_t *b; ngx_chain_t out; ngx_atomic_int_t ap, hn, ac, rq, rd, wr; 这个模块要求接受的请求类是 GET、HEAD，其他类型的请求会被拒绝。
if (r->method != NGX_HTTP_GET && r->method != NGX_HTTP_HEAD) { return NGX_HTTP_NOT_ALLOWED; } 放弃请求体，因为这个模块用不上。
rc = ngx_http_discard_request_body(r); if (rc != NGX_OK) { return rc; } 如果请求是 HEAD 类型的，则直接设置响应头的 content_type、status 字段，并发送响应头。
ngx_str_set(&r->headers_out.content_type, "text/plain"); if (r->method == NGX_HTTP_HEAD) { r->headers_out.status = NGX_HTTP_OK; rc = ngx_http_send_header(r); if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) { return rc; } } 创建一个缓冲区，向缓冲区写入我们上面在浏览器中看到的东西。
size = sizeof("Active connections: \n") + NGX_ATOMIC_T_LEN + sizeof("server accepts handled requests\n") - 1 + 6 + 3 * NGX_ATOMIC_T_LEN + sizeof("Reading: Writing: Waiting: \n") + 3 * NGX_ATOMIC_T_LEN; b = ngx_create_temp_buf(r->pool, size); if (b == NULL) { return NGX_HTTP_INTERNAL_SERVER_ERROR; } out.buf = b; out.next = NULL; ap = *ngx_stat_accepted; hn = *ngx_stat_handled; ac = *ngx_stat_active; rq = *ngx_stat_requests; rd = *ngx_stat_reading; wr = *ngx_stat_writing; // 封装了 sprintf b->last = ngx_sprintf(b->last, "Active connections: %uA \n", ac); // 封装了 memcpy b->last = ngx_cpymem(b->last, "server accepts handled requests\n", sizeof("server accepts handled requests\n") - 1); b->last = ngx_sprintf(b->last, " %uA %uA %uA \n", ap, hn, rq); b->last = ngx_sprintf(b->last, "Reading: %uA Writing: %uA Waiting: %uA \n", rd, wr, ac - (rd + wr)); 缓冲区写完了。然后设置下响应头的 status、content_length_n（还记得吗？b->last - b->pos 刚好是缓冲区的第二个区域，是已写入数据部分。）
r->headers_out.status = NGX_HTTP_OK; r->headers_out.content_length_n = b->last - b->pos; b->last_buf = 1;
发送响应头。
rc = ngx_http_send_header(r); if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) { return rc; } filter。
return ngx_http_output_filter(r, &out);}
5 Reference
- http://wiki.nginx.org/HttpStubStatusModule
- http://blog.csdn.net/lengzijian/article/details/7356064
- http://www.codinglabs.org/html/intro-of-nginx-module-development.html