Nginx output processing process

During the HTTP processing process, we will continue to see several functions. Let’s talk about

      static ngx_int_t ngx_http_echo_handler(ngx_http_request_t *r)
{
       ngx_int_t rc;
       ngx_buf_t *b; 
       //ngx_chain_t是关于ngx_buf_t的一个链表
       ngx_chain_t out; 
       ngx_http_echo_loc_conf_t *elcf; //读取我们写在nginx.conf文件中的配置信息
       elcf = ngx_http_get_module_loc_conf(r, ngx_http_echo_module);
       if(!(r->method &  (NGX_HTTP_HEAD|NGX_HTTP_GET|NGX_HTTP_POST))) 
       { 
         return NGX_HTTP_NOT_ALLOWED; 
       }
      //headers_out我们可以认为是响应头部的处理
       r->headers_out.content_type.len = sizeof("text/html") - 1;
       r->headers_out.content_type.data = (u_char *) "text/html";
       r->headers_out.status = NGX_HTTP_OK; 
       r->headers_out.content_length_n = elcf->ed.len; 
       if(r->method == NGX_HTTP_HEAD) { 
           rc = ngx_http_send_header(r); 
           if(rc != NGX_OK) { 
               return rc; 
         } 
      } 
       b = ngx_pcalloc(r->pool, sizeof(ngx_buf_t)); 
       if(b == NULL) 
        {
             ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "Failed to allocate response buffer."); 
             return NGX_HTTP_INTERNAL_SERVER_ERROR; 
        } 
       //设置ngx_chain_t中的ngx_buf_t链表，next为NULL则说明该链表结束
       out.buf = b; 
       out.next = NULL; 
       //设置缓存内容
       b->pos = elcf->ed.data; 
       b->last = elcf->ed.data + (elcf->ed.len);
       b->memory = 1;
       //当前ngx_buf_t已经是ngx_chain_t链表中的最后一项 
       b->last_buf = 1; 
       rc = ngx_http_send_header(r); 
       if(rc != NGX_OK) 
       {
          return rc; 
        } 
     return ngx_http_output_filter(r, &out);
} 

first. Just like what appears in our code, now parse two functions, one of which is ngx_http_send_request. The code is as follows

 ngx_http_send_header(ngx_http_request_t *r)
 {
     if (r->header_sent) {
         ngx_log_error(NGX_LOG_ALERT, r->connection->log, 0,
                       "header already sent");
         return NGX_ERROR;
     }
 
     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);
 }

. The implementation of this code is not straightforward. It is a sending function, but the request header is processed according to the ngx_http_top_header_filter chain list of the filter module. Next is the ngx_http_output_filter function.

The function is defined as follows:

 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;
 
     ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                    "http output filter \"%V?%V\"", &r->uri, &r->args);
 
     rc = ngx_http_top_body_filter(r, in);
 
     if (rc == NGX_ERROR) {
         /* NGX_ERROR may be returned by any filter */
         c->error = 1;
     }
 
     return rc;
}

can see that ngx_http_output_filter finally calls the ngx_http_top_body_filter function, which uses There are two parameters, one is the ngx_http_request_t request and the other is the ngx_chain_t linked list. In fact, the passed ngx_chain_t is added to the tail of the request out (also of the ngx_chain_t data type), and its content is added to the tail when outputting. Such a page is output

The above introduces the Nginx output processing process, including various aspects. I hope it will be helpful to friends who are interested in PHP tutorials.