'In-depth understanding of Nginx' notes: ngx_event_pipe_s structure

<code><span>typedef</span><span>struct</span> ngx_event_pipe_s  ngx_event_pipe_t;

<span>// 处理接收自上游的包体的回调函数原型</span><span>typedef</span> ngx_int_t (*ngx_event_pipe_input_filter_pt)(ngx_event_pipe_t *p,
                                                    ngx_buf_t *buf);

<span>// 向下游发送响应的回调函数原型</span><span>typedef</span> ngx_int_t (*ngx_event_pipe_output_filter_pt)(<span>void</span> *data,
                                                     ngx_chain_t *chain);



<span>struct</span> ngx_event_pipe_s {
     <span>// Nginx与上游服务器之间的连接</span>
    ngx_connection_t  *upstream;

    <span>// Nginx与下游客户端之间的连接</span>
    ngx_connection_t  *downstream;

     <span>/* 直接接收自上游服务器的缓冲区链表，保存的是未经任何处理的数据。这个链表是逆序的，后接受的响应插在链表头处 */</span>
    ngx_chain_t       *free_raw_bufs;

    <span>// 表示接收到的上游响应缓冲区，其数据是经过input_filter处理的</span>
    ngx_chain_t       *in;

    <span>// 指向刚收到的一个缓冲区</span>
    ngx_chain_t      **last_in;

     <span>// 保存着将要发给客户端的缓冲区链表。在写入临时文件成功时，会把in中的缓冲区添加到out中</span>
    ngx_chain_t       *out;

    <span>// 等待释放的缓冲区</span>
    ngx_chain_t       *<span>free</span>;

    <span>// 表示上次调用ngx_http_output_filter函数发送响应时没有发送完的缓冲区链表</span>
    ngx_chain_t       *busy;

    <span>/*
     * the input filter i.e. that moves HTTP/1.1 chunks
     * from the raw bufs to an incoming chain
     */</span><span>// 处理接收到的、来自上游服务器的数据</span>
    ngx_event_pipe_input_filter_pt    input_filter;

    <span>// 用于input_filter的的参数，一般是ngx_http_request_t的地址</span><span>void</span>                             *input_ctx;

     <span>// 向下游发送响应的函数</span>
    ngx_event_pipe_output_filter_pt   output_filter;

    <span>// output_filter的参数，指向ngx_http_request_t</span><span>void</span>                             *output_ctx;

     <span>// 1：表示当前已读取到上游的响应</span><span>unsigned</span>           read:<span>1</span>;

    <span>// 1：启用文件缓存</span><span>unsigned</span>           cacheable:<span>1</span>;

    <span>// 1：表示接收上游响应时，一次只能接收一个ngx_buf_t缓冲区</span><span>unsigned</span>           single_buf:<span>1</span>;

    <span>// 1：一旦不再接收上游包体，将尽可能地释放缓冲区</span><span>unsigned</span>           free_bufs:<span>1</span>;

    <span>// 1：表示Nginx与上游交互已经结束</span><span>unsigned</span>           upstream_done:<span>1</span>;

    <span>// 1：Nginx与上游服务器的连接出现错误</span><span>unsigned</span>           upstream_error:<span>1</span>;

    <span>// 1：表示与上游服务器的连接已关闭</span><span>unsigned</span>           upstream_eof:<span>1</span>;

    <span>/* 1：表示暂时阻塞读取上游响应的的流程。此时会先调用ngx_event_pipe_write_to_downstream
    函数发送缓冲区中的数据给下游，从而腾出缓冲区空间，再调用ngx_event_pipe_read_upstream
    函数读取上游信息 */</span><span>unsigned</span>           upstream_blocked:<span>1</span>;

    <span>// 1：与下游的交互已结束</span><span>unsigned</span>           downstream_done:<span>1</span>;

    <span>// 1：与下游的连接出现错误</span><span>unsigned</span>           downstream_error:<span>1</span>;

    <span>// 1：复用临时文件。它是由ngx_http_upstream_conf_t中的同名成员赋值的</span><span>unsigned</span>           cyclic_temp_file:<span>1</span>;

     <span>// 已分配的缓冲区数据</span>
    ngx_int_t          allocated;

    <span>// 记录了接收上游响应的内存缓冲区大小，bufs.size表示每个内存缓冲区大小，bufs.num表示最多可以有num个缓冲区</span>
    ngx_bufs_t         bufs;

    <span>// 用于设置、比较缓冲区链表中的ngx_buf_t结构体的tag标志位</span>
    ngx_buf_tag_t      tag;

     <span>/* busy缓冲区中待发送响应长度的最大值，当到达busy_size时，必须等待busy缓冲区发送了足够的数据，
     才能继续发送out和in中的内容 */</span>
    ssize_t            busy_size;

     <span>// 已经接收到来自上游响应包体的长度</span>
    off_t              read_length;
    off_t              length;

     <span>// 表示临时文件的最大长度</span>
    off_t              max_temp_file_size;

    <span>// 表示一次写入文件时数据的最大长度</span>
    ssize_t            temp_file_write_size;

     <span>// 读取上游响应的超时时间</span>
    ngx_msec_t         read_timeout;

    <span>// 向下游发送响应的超时时间</span>
    ngx_msec_t         send_timeout;

    <span>// 向下游发送响应时，TCP连接中设置的send_lowat“水位”</span>
    ssize_t            send_lowat;

     <span>// 连接池</span>
    ngx_pool_t        *pool;

    <span>// 日志</span>
    ngx_log_t         *<span>log</span>;

     <span>// 表示在接收上游服务器响应头部阶段，已经读取到响应包体</span>
    ngx_chain_t       *preread_bufs;

    <span>// 表示在接收上游服务器响应头部阶段，已经读取到响应包体长度</span>
    size_t             preread_size;

    <span>// 用于缓存文件</span>
    ngx_buf_t         *buf_to_file;
    size_t             limit_rate;
    time_t             start_sec;

     <span>// 存放上游响应的临时文件</span>
    ngx_temp_file_t   *temp_file;

     <span>// 已使用的ngx_buf_t缓冲区数目</span><span>/* STUB */</span><span>int</span>     num;
};
</code>