nginx 的ngx_http_addition_module 模块也是一个修改content 的好东西，对于openresty 我们经常使用content_by_lua 阶段处理
但是经过分析ngx_http_addition_module 源码的处理机制，他是基于body_fiter 处理的，所以我们基于content_by_lua 进行数据处理
会有顺序不对的问题

参考源码处理

处理机制
ngx_http_addition_filter_module_ctx上下文定义

static ngx_http_module_t  ngx_http_addition_filter_module_ctx = {

    NULL,                                  /* preconfiguration */

    ngx_http_addition_filter_init,         /* postconfiguration */

    NULL,                                  /* create main configuration */

    NULL,                                  /* init main configuration */

    NULL,                                  /* create server configuration */

    NULL,                                  /* merge server configuration */

    ngx_http_addition_create_conf,         /* create location configuration */

    ngx_http_addition_merge_conf           /* merge location configuration */

};

阶段(依赖了header 以及body)

static ngx_int_t

ngx_http_addition_filter_init(ngx_conf_t *cf)

{

    ngx_http_next_header_filter = ngx_http_top_header_filter;

    ngx_http_top_header_filter = ngx_http_addition_header_filter;

    ngx_http_next_body_filter = ngx_http_top_body_filter;

    ngx_http_top_body_filter = ngx_http_addition_body_filter;

    return NGX_OK;

}

核心处理

static ngx_int_t

ngx_http_addition_body_filter(ngx_http_request_t *r, ngx_chain_t *in)

{

    ngx_int_t                  rc;

    ngx_uint_t                 last;

    ngx_chain_t               *cl;

    ngx_http_request_t        *sr;

    ngx_http_addition_ctx_t   *ctx;

    ngx_http_addition_conf_t  *conf;

    if (in == NULL || r->header_only) {

        return ngx_http_next_body_filter(r, in);

    }

    ctx = ngx_http_get_module_ctx(r, ngx_http_addition_filter_module);

    if (ctx == NULL) {

        return ngx_http_next_body_filter(r, in);

    }

    conf = ngx_http_get_module_loc_conf(r, ngx_http_addition_filter_module);

    if (!ctx->before_body_sent) {

        ctx->before_body_sent = 1;

        if (conf->before_body.len) {

            if (ngx_http_subrequest(r, &conf->before_body, NULL, &sr, NULL, 0)

                != NGX_OK)

            {

                return NGX_ERROR;

            }

        }

    }

    if (conf->after_body.len == 0) {

        ngx_http_set_ctx(r, NULL, ngx_http_addition_filter_module);

        return ngx_http_next_body_filter(r, in);

    }

    last = 0;

    for (cl = in; cl; cl = cl->next) {

        if (cl->buf->last_buf) {

            cl->buf->last_buf = 0;

            cl->buf->last_in_chain = 1;

            cl->buf->sync = 1;

            last = 1;

        }

    }

    rc = ngx_http_next_body_filter(r, in);

    if (rc == NGX_ERROR || !last || conf->after_body.len == 0) {

        return rc;

    }

    if (ngx_http_subrequest(r, &conf->after_body, NULL, &sr, NULL, 0)

        != NGX_OK)

    {

        return NGX_ERROR;

    }

    ngx_http_set_ctx(r, NULL, ngx_http_addition_filter_module);

    return ngx_http_send_special(r, NGX_HTTP_LAST);

}

如果需要使用的解决方法

可以直接在body_fiter 阶段进行数据处理，注意此阶段会有一些api 的限制
参考处理（直接输出了，比较简单）

location = /flush2.html {

    add_before_body /before_action;

    add_after_body  /after_action;

}

location  /before_action {

    default_type text/html;

    content_by_lua_block {

            ngx.say("this is before content\n")

            ngx.log(ngx.ERR, "before_action")

    }

}

location  /after_action {

    default_type text/html;

    body_filter_by_lua_block {

              ngx.arg[1] = "this is after content\n"

    }

}

说明

以上是结合源码学习ngx_http_addition_module 与openresty 集成的处理，大家如果碰到类似问题可以参考

参考资料

https://github.com/nginx/nginx/blob/master/src/http/modules/ngx_http_addition_filter_module.c#L133