1 nginx过滤模块简介
过滤（filter）模块是过滤响应头和内容的模块，可以对回复的头和内容进行处理。它的处理时间在获取回复内容之后，
向用户发送响应之前。它的处理过程分为两个阶段，过滤HTTP回复的头部和主体，在这两个阶段可以分别对头部和主体
进行修改。
2 过滤模块执行顺序
2.1 ngx_http_output_(head, body)_filter_pt
先看一下nginx常用的过滤模块，在ngx_moudles.c中有一下代码：
ngx_module_t *ngx_modules[] = {
......
&ngx_http_write_filter_module,
&ngx_http_header_filter_module,
&ngx_http_chunked_filter_module,
&ngx_http_range_header_filter_module,
&ngx_http_gzip_filter_module,
&ngx_http_postpone_filter_module,
&ngx_http_ssi_filter_module,
&ngx_http_charset_filter_module,
&ngx_http_userid_filter_module,
&ngx_http_myfilter_module,
&ngx_http_headers_filter_module,
&ngx_http_copy_filter_module,
&ngx_http_range_body_filter_module,
&ngx_http_not_modified_filter_module,
NULL
};
nginx过滤模块的执行顺序是从ngx_http_not_modified_filter_module 到 ngx_http_write_filter_module。下面我们来看一下这个执行
顺序是怎么用链表构成的。
既然是用链表构成的，肯定是要有链表指针，而且有两个，一个链接处理头部的函数，一个链接处理包体的函数，下面来看看这两
个链表指针的定义：
typedef ngx_int_t (ngx_http_output_header_filter_pt)(ngx_http_request_t *r); typedef ngx_int_t (ngx_http_output_body_filter_pt)(ngx_http_request_t *r, ngx_chain_t *in);
ngx_http_output_header_filter_pt 指向处理头部的函数指针，每一个过滤模块中如果要处理头部，就必要定义一个局部的这种类型的指针和函数。
ngx_http_output_body_filter_pt 指向处理包体的函数指针，每一个过滤模块中如果要处理包体，就必要定义一个局部的这种类型的指针和函数。
2.2 过滤模块链表的入口
过滤模块链表的入口是两个静态的函数指针：
extern ngx_http_output_header_filter_pt ngx_http_top_header_filter; extern ngx_http_output_body_filter_pt ngx_http_body_body_filter;
当执行ngx_http_send_header发送http头部时，就开始从ngx_http_tou_header_filter指针遍历所有的http头部过滤模块。
ngx_http_send_header:
ngx_int_t
ngx_http_send_header(ngx_http_request_t *r)
{
if (r->err_status) {
r->headers_out.status = r->err_status;
r->headers_out.status_line.len = 0;
}
return ngx_http_top_header_filter(r);//链表头，指向第一个过滤头部的模块函数
}
当执行ngx_http_output_filter发送包体时，就从ngx_http_top_body_filter指针遍历所有的http包体过滤模块。
ngx_http_output_filter:
ngx_int_t
ngx_http_output_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
ngx_int_t rc;
ngx_connection_t *c;
c = r->connection;
rc = ngx_http_top_body_filter(r, in);
if (rc == NGX_ERROR) {
c->error = 1;
}
return rc;//链表头，指向第一个过滤包体的模块函数
}2.3 过滤模块的链接
原来每个过滤模块都定义了两个（这里假设每个过滤模块都处理头部和包体）static的函数指针：
static ngx_http_output_header_filter_pt ngx_http_next_header_filter; static ngx_http_output_body_filter_pt ngx_http_next_body_filter;
ngx_http_next_header_filter来保存ngx_http_top_header_filter指向的处理模块函数，而ngx_http_top_header_filter则指向本模块处理头部的过滤函数。
ngx_http_next_body_filter来保存ngx_http_top_body_filter指向的处理模块函数，而ngx_http_top_body_filter则指向本模块处理包体的过滤函数。
代码表示如下：
ngx_http_next_header_filter = ngx_http_top_header_filter; ngx_http_top_header_filter = ngx_http_current_myfilter_header_filter;//处理头部的过滤函数 ngx_http_next_body_filter = ngx_http_top_body_filter; ngx_http_top_body_filter = ngx_http_current_myfilter_body_filter;//处理包体的过滤函数
这样所有过滤模块就被链接起来了。
比如现在有两个过滤模块filter_a, filter_b，filter_a模块先定义，filter_b模块后定义。
在filter_a 里面有如下代码：
ngx_http_next_header_filter_a = ngx_http_top_header_filter; ngx_http_top_header_filter = ngx_http_filtera_header_filter; ngx_http_next_body_filter_a = ngx_http_top_body_filter; ngx_http_top_body_filter = ngx_http_filtera_body_filter;
注意这时ngx_http_header_filter指向filter_a的头部处理函数，ngx_http_top_body_filter指向filter_a的包体处理函数。
在filter_b里面有如下代码：
ngx_http_next_header_filter_b = ngx_http_top_header_filter; ngx_http_top_header_filter = ngx_http_filterb_header_filter; ngx_http_next_body_filter_b = ngx_http_top_body_filter; ngx_http_top_body_filter = ngx_http_filterb_body_filter;
同样，ngx_http_next_body_filter_b保存的是ngx_http_filterb_body_filter,即指向filtera中处理包体的过滤函数，filtera和filterb的包体过滤链表就建立起来了。
而此时ngx_http_top_header_filter保存的是filterb的头部过滤函数，ngx_http_top_body_filter保存的是filterb的包体过滤函数。
我们实现filterb的头部过滤函数时的代码往往如下：
ngx_int_t ngx_http_next_header_filter_b(ngx_http_request_r *r)
{
//处理头部的代码
......
return ngx_http_next_header_filter_b(r, in);//调用filtera处理头部的函数
}实现filterb的包体过滤函数时的代码往往如下：
ngx_int_t ngx_http_next_body_filter_b(ngx_http_request_t *r, ngx_chain_t *in)
{
//处理包体的代码
......
return ngx_http_header_filter_b(r, in); //调用filtera处理包体的函数
}假如有模块filterc、filterd......都是按照filtera和filterb链接的方式链接在两个链表中的。
3实现一个简单的过滤模块
实现一个简单的过滤模块在头部加入字符串"[my filter prefix] "。
3.1config的编写：
ngx_addon_name=ngx_http_myfilter_module HTTP_FILTER_MODULES="$HTTP_FILTER_MODULES ngx_http_myfilter_module" NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_myfilter_module.c"
刚开始我就在这里跳进坑了，找了好久，原来不是handler模块中写的HTTP_MODULES。
3.2代码编写
其实实现挺简单的分为几个步骤：
1）三个模块结构体的实现：ngx_command_t 、ngx_http_moudle_t、ngx_moudle_t可以参考这篇文章
2）把当前处理头部和包体的过滤函数链接如链表
3）分别实现过滤头部的函数和过滤包体的函数
第一步 代码：
typedef struct
{
ngx_flag_t arg_flag;
}ngx_http_myfilter_loc_conf_t;
typedef struct
{
ngx_int_t flag_count;
}ngx_http_myfilter_ctx_t;
static ngx_str_t filter_prefix = ngx_string("[my filter prefix]");
//static限定这两个变量只在当前文件中有效
static ngx_http_output_header_filter_pt ngx_http_next_header_filter;
static ngx_http_output_body_filter_pt ngx_http_next_body_filter;
static char* ngx_http_myfilter_set(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);
static void* ngx_http_myfilter_create_loc_conf(ngx_conf_t *cf);
static char* ngx_http_myfilter_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child);
static ngx_int_t ngx_http_myfilter_post_config(ngx_conf_t *cf);
static ngx_int_t ngx_http_myfilter_header_filter(ngx_http_request_t *r);
static ngx_int_t ngx_http_myfilter_body_filter(ngx_http_request_t *r, ngx_chain_t *in);
static ngx_command_t ngx_http_myfilter_commands[] =
{
{
ngx_string("add_prefix"),
NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
ngx_http_myfilter_set,
NGX_HTTP_LOC_CONF_OFFSET,
offsetof(ngx_http_myfilter_loc_conf_t, arg_flag),
NULL
},
ngx_null_command
};
static ngx_http_module_t ngx_http_myfilter_module_ctx =
{
NULL,
ngx_http_myfilter_post_config,
NULL,
NULL,
NULL,
NULL,
ngx_http_myfilter_create_loc_conf,
ngx_http_myfilter_merge_loc_conf
};
ngx_module_t ngx_http_myfilter_module =
{
NGX_MODULE_V1,
&ngx_http_myfilter_module_ctx,
ngx_http_myfilter_commands,
NGX_HTTP_MODULE,
NULL,
NULL,
NULL,
NULL,
NULL,
NULL,
NULL,
NGX_MODULE_V1_PADDING
};
static ngx_int_t ngx_http_myfilter_post_config(ngx_conf_t *cf)
{
ngx_http_next_header_filter = ngx_http_top_header_filter;
ngx_http_top_header_filter = ngx_http_myfilter_header_filter;
ngx_http_next_body_filter = ngx_http_top_body_filter;
ngx_http_top_body_filter = ngx_http_myfilter_body_filter;
ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "post config is called!");
return NGX_OK;
}
static ngx_int_t ngx_http_myfilter_header_filter(ngx_http_request_t *r)
{
if (r->headers_out.status != NGX_HTTP_OK)
{
ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "headers_out.status = %d", r->headers_out.status);
return ngx_http_next_header_filter(r);
}
ngx_http_myfilter_loc_conf_t *mlcf;
mlcf = ngx_http_get_module_loc_conf(r, ngx_http_myfilter_module);
if (mlcf->arg_flag == 0) //flag = 0,表示不加前缀
{
ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "arg_flag = 0");
return ngx_http_next_header_filter(r);
}
ngx_http_myfilter_ctx_t *mctx;
mctx = ngx_http_get_module_ctx(r, ngx_http_myfilter_module);
if (mctx != NULL) //mctx不为空，表示这个头部已经处理过，不许要再处理了
{
return ngx_http_next_header_filter(r);
}
mctx = ngx_pcalloc(r->pool, sizeof(ngx_http_myfilter_ctx_t));
if (mctx == NULL)
{
return NGX_ERROR;
}
ngx_http_set_ctx(r, mctx, ngx_http_myfilter_module);
mctx->flag_count = 0; //0：初始化为不加前缀
ngx_str_t type = ngx_string("text/plain");
if (r->headers_out.content_type.len >= type.len
&& ngx_strncasecmp(r->headers_out.content_type.data, type.data, type.len) == 0)
{
mctx->flag_count = 1; //1：头部类型为“text/plain”的要加前缀
if (r->headers_out.content_length_n > 0)
{
r->headers_out.content_length_n += filter_prefix.len;
}
}
return ngx_http_next_header_filter(r);
}
static ngx_int_t ngx_http_myfilter_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
ngx_http_myfilter_ctx_t *mctx;
mctx = ngx_http_get_module_ctx(r, ngx_http_myfilter_module);
if (mctx == NULL || mctx->flag_count != 1)
{
return ngx_http_next_body_filter(r, in);
}
mctx->flag_count = 2;
ngx_buf_t* buf = ngx_create_temp_buf(r->pool, filter_prefix.len);
buf->start = filter_prefix.data;
buf->pos = filter_prefix.data;
buf->last = filter_prefix.data + filter_prefix.len;
ngx_chain_t* out = ngx_alloc_chain_link(r->pool);
out->buf = buf;
out->next = in;
return ngx_http_next_body_filter(r, out);
}
http://blog.csdn.net/xiaoliangsky/article/details/39522357
完整代码以后参考：
#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_http.h>
typedef struct
{
ngx_flag_t arg_flag;
}ngx_http_myfilter_loc_conf_t;
typedef struct
{
ngx_int_t flag_count;
}ngx_http_myfilter_ctx_t;
static ngx_str_t filter_prefix = ngx_string("[my filter prefix]");
//static限定这两个变量只在当前文件中有效
static ngx_http_output_header_filter_pt ngx_http_next_header_filter;
static ngx_http_output_body_filter_pt ngx_http_next_body_filter;
static char* ngx_http_myfilter_set(ngx_conf_t *cf, ngx_command_t *cmd, void *conf);
static void* ngx_http_myfilter_create_loc_conf(ngx_conf_t *cf);
static char* ngx_http_myfilter_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child);
static ngx_int_t ngx_http_myfilter_post_config(ngx_conf_t *cf);
static ngx_int_t ngx_http_myfilter_header_filter(ngx_http_request_t *r);
static ngx_int_t ngx_http_myfilter_body_filter(ngx_http_request_t *r, ngx_chain_t *in);
static ngx_command_t ngx_http_myfilter_commands[] =
{
{
ngx_string("add_prefix"),
NGX_HTTP_LOC_CONF|NGX_CONF_FLAG,
ngx_http_myfilter_set,
NGX_HTTP_LOC_CONF_OFFSET,
offsetof(ngx_http_myfilter_loc_conf_t, arg_flag),
NULL
},
ngx_null_command
};
static ngx_http_module_t ngx_http_myfilter_module_ctx =
{
NULL,
ngx_http_myfilter_post_config,
NULL,
NULL,
NULL,
NULL,
ngx_http_myfilter_create_loc_conf,
ngx_http_myfilter_merge_loc_conf
};
ngx_module_t ngx_http_myfilter_module =
{
NGX_MODULE_V1,
&ngx_http_myfilter_module_ctx,
ngx_http_myfilter_commands,
NGX_HTTP_MODULE,
NULL,
NULL,
NULL,
NULL,
NULL,
NULL,
NULL,
NGX_MODULE_V1_PADDING
};
static ngx_int_t ngx_http_myfilter_post_config(ngx_conf_t *cf)
{
ngx_http_next_header_filter = ngx_http_top_header_filter;
ngx_http_top_header_filter = ngx_http_myfilter_header_filter;
ngx_http_next_body_filter = ngx_http_top_body_filter;
ngx_http_top_body_filter = ngx_http_myfilter_body_filter;
ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "post config is called!");
return NGX_OK;
}
static char* ngx_http_myfilter_set(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
ngx_http_myfilter_loc_conf_t *mlcf = conf;
char* rc = ngx_conf_set_flag_slot(cf, cmd, conf);
ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "arg_flag = %d", mlcf->arg_flag);
return rc;
}
static void* ngx_http_myfilter_create_loc_conf(ngx_conf_t *cf)
{
ngx_http_myfilter_loc_conf_t *mlcf;
mlcf = ngx_pcalloc(cf->pool, sizeof(ngx_http_myfilter_loc_conf_t));
if (mlcf == NULL)
{
return NULL;
}
mlcf->arg_flag = NGX_CONF_UNSET;
return mlcf;
}
static char* ngx_http_myfilter_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
{
ngx_http_myfilter_loc_conf_t* prev = parent;
ngx_http_myfilter_loc_conf_t* conf = child;
ngx_conf_merge_value(conf->arg_flag, prev->arg_flag, 0);
return NGX_CONF_OK;
}
static ngx_int_t ngx_http_myfilter_header_filter(ngx_http_request_t *r)
{
if (r->headers_out.status != NGX_HTTP_OK)
{
ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "headers_out.status = %d", r->headers_out.status);
return ngx_http_next_header_filter(r);
}
ngx_http_myfilter_loc_conf_t *mlcf;
mlcf = ngx_http_get_module_loc_conf(r, ngx_http_myfilter_module);
if (mlcf->arg_flag == 0) //flag = 0,表示不加前缀
{
ngx_log_error(NGX_LOG_EMERG, r->connection->log, 0, "arg_flag = 0");
return ngx_http_next_header_filter(r);
}
ngx_http_myfilter_ctx_t *mctx;
mctx = ngx_http_get_module_ctx(r, ngx_http_myfilter_module);
if (mctx != NULL) //mctx不为空，表示这个头部已经处理过，不许要再处理了
{
return ngx_http_next_header_filter(r);
}
mctx = ngx_pcalloc(r->pool, sizeof(ngx_http_myfilter_ctx_t));
if (mctx == NULL)
{
return NGX_ERROR;
}
ngx_http_set_ctx(r, mctx, ngx_http_myfilter_module);
mctx->flag_count = 0; //0：初始化为不加前缀
ngx_str_t type = ngx_string("text/plain");
if (r->headers_out.content_type.len >= type.len
&& ngx_strncasecmp(r->headers_out.content_type.data, type.data, type.len) == 0)
{
mctx->flag_count = 1; //1：头部类型为“text/plain”的要加前缀
if (r->headers_out.content_length_n > 0)
{
r->headers_out.content_length_n += filter_prefix.len;
}
}
return ngx_http_next_header_filter(r);
}
static ngx_int_t ngx_http_myfilter_body_filter(ngx_http_request_t *r, ngx_chain_t *in)
{
ngx_http_myfilter_ctx_t *mctx;
mctx = ngx_http_get_module_ctx(r, ngx_http_myfilter_module);
if (mctx == NULL || mctx->flag_count != 1)
{
return ngx_http_next_body_filter(r, in);
}
mctx->flag_count = 2;
ngx_buf_t* buf = ngx_create_temp_buf(r->pool, filter_prefix.len);
buf->start = filter_prefix.data;
buf->pos = filter_prefix.data;
buf->last = filter_prefix.data + filter_prefix.len;
ngx_chain_t* out = ngx_alloc_chain_link(r->pool);
out->buf = buf;
out->next = in;
return ngx_http_next_body_filter(r, out);
}
在nginx/html文件里面创建一个test.txt，内容为：hhhhh。
然后在浏览器中输入：localhost/test.txt
nginx 学习五 filter模块简介和实现一个简单的filter模块
原文地址：http://blog.csdn.net/xiaoliangsky/article/details/39522357
