Nginx add custom header

公司客户端需要读取HEADER中的length字段，length字段的值与Content-Length值一样。以前是通过在apache中写一个perl模块实现的，现在切换为Nginx，需要开发Nginx模块。用C写Nginx模块还是比较简单的，可以通过HeaderFilter实现这个功能。就是在响应数据准备好以后，发送给客户端之前，增加我们的功能。

首先config文件对filter模块和其它处理模块配置不一样：

我的config:

ngx_addon_name=ngx_http_sukai_addlength_module
HTTP_AUX_FILTER_MODULES="$HTTP_AUX_FILTER_MODULES ngx_http_sukai_addlength_module"
NGX_ADDON_SRCS="$NGX_ADDON_SRCS $ngx_addon_dir/ngx_http_sukai_addlength_module.c"

创建文件ngx_http_sukai_addlength_module.c：

/*
 * Copyright (C) Kai.Su MSN:[email protected] QQ:417331518
 * ./configure --with-pcre=/usr/local/src/pcre-8.12 --prefix=/byread/bin/nginx --with-http_stub_status_module --with-http_perl_module --with-perl=/byread/bin/perl/bin/perl --add-module=/usr/local/src/nginx-0.8.54/sukai-addlength-module
 */

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


typedef struct {
        ngx_flag_t enable;
} ngx_http_sukai_addlength_loc_conf_t;


static ngx_http_output_header_filter_pt ngx_http_next_header_filter;

static void* ngx_http_sukai_addlength_create_loc_conf(ngx_conf_t *cf);
static char* ngx_http_sukai_addlength_merge_loc_conf(ngx_conf_t *cf,
    void *parent, void *child);


static ngx_int_t
ngx_http_sukai_addlength_filter_init(ngx_conf_t *cf);

static ngx_command_t ngx_http_sukai_addlength_module_commands[] = {
        { ngx_string("enable_addlength"),
                NGX_HTTP_LOC_CONF|NGX_CONF_TAKE1,
                ngx_conf_set_flag_slot,
                NGX_HTTP_LOC_CONF_OFFSET,
                0,
                NULL },

        ngx_null_command
};

static ngx_http_module_t ngx_http_sukai_addlength_module_ctx = {
        NULL, /* preconfiguration */
        ngx_http_sukai_addlength_filter_init, /* postconfiguration */

        NULL, /* create main configuration */
        NULL, /* init main configuration */

        NULL, /* create server configuration */
        NULL, /* merge server configuration */

        ngx_http_sukai_addlength_create_loc_conf, /* create location configuration */
        ngx_http_sukai_addlength_merge_loc_conf /* merge location configuration */
};


ngx_module_t ngx_http_sukai_addlength_module = {
        NGX_MODULE_V1,
        &ngx_http_sukai_addlength_module_ctx, /* module context */
        ngx_http_sukai_addlength_module_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_sukai_addlength_header_filter(ngx_http_request_t *r)
{
        ngx_http_sukai_addlength_loc_conf_t *conf;
        conf = ngx_http_get_module_loc_conf(r, ngx_http_sukai_addlength_module);
        if(conf->enable) {
			ngx_table_elt_t *length_header = (ngx_table_elt_t *)ngx_list_push(&r->headers_out.headers);
			if (length_header != NULL) 
			{
				length_header->hash = 1;
				length_header->key.len = sizeof("length") - 1;
				length_header->key.data = (u_char *)"length";
				ngx_buf_t *b;
				b = ngx_create_temp_buf(r->pool, sizeof(off_t));
				b->last = ngx_sprintf(b->last, "%O", r->headers_out.content_length_n);
				b->memory = 1;
				b->last_buf = 1;
				length_header->value.len = b->last - b->start;
				length_header->value.data = b->start;
			}
			ngx_table_elt_t *my_header = (ngx_table_elt_t *)ngx_list_push(&r->headers_out.headers);
			if (my_header != NULL) 
			{
				my_header->hash = 1;
				my_header->key.len = sizeof("Mod-Author") - 1;
				my_header->key.data = (u_char *)"Mod-Author";
				my_header->value.len = sizeof("sukai,[email protected]") - 1;
				my_header->value.data = (u_char *)"sukai,[email protected]";
			}
        }
        return ngx_http_next_header_filter(r);
}




static ngx_int_t
ngx_http_sukai_addlength_filter_init(ngx_conf_t *cf)
{
        ngx_http_next_header_filter = ngx_http_top_header_filter;
        ngx_http_top_header_filter = ngx_http_sukai_addlength_header_filter;
        return NGX_OK;
}

static void *
ngx_http_sukai_addlength_create_loc_conf(ngx_conf_t *cf)
{
    ngx_http_sukai_addlength_loc_conf_t *conf;

    conf = ngx_pcalloc(cf->pool, sizeof(ngx_http_sukai_addlength_loc_conf_t));
    if (conf == NULL) {
        return NGX_CONF_ERROR;
    }

    conf->enable = NGX_CONF_UNSET;
    return conf;
}

static char *
ngx_http_sukai_addlength_merge_loc_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_http_sukai_addlength_loc_conf_t *prev = parent;
    ngx_http_sukai_addlength_loc_conf_t *conf = child;

    ngx_conf_merge_value(conf->enable, prev->enable, 0);

    return NGX_CONF_OK;
}