http v2 analyze

Author: yazhou.yang

nginx-1.9.2/objs/nginx

@@ -248,14 +248,16 @@ typedef enum {
     ngx_event_t        *write; //连接对应的写事件  赋值在ngx_event_process_init 一般在ngx_handle_write_event中添加些事件，空间是从ngx_cycle_t->read_event池子中获取的
 
     ngx_socket_t        fd;//套接字句柄
-
+    /* 如果启用了ssl,则发送和接收数据在ngx_ssl_recv ngx_ssl_write ngx_ssl_recv_chain ngx_ssl_send_chain */
     //服务端通过ngx_http_wait_request_handler读取数据
     ngx_recv_pt         recv; //直接接收网络字符流的方法  见ngx_event_accept或者ngx_http_upstream_connect   赋值为ngx_os_io  在接收到客户端连接或者向上游服务器发起连接后赋值
     ngx_send_pt         send; //直接发送网络字符流的方法  见ngx_event_accept或者ngx_http_upstream_connect   赋值为ngx_os_io  在接收到客户端连接或者向上游服务器发起连接后赋值
 
+    /* 如果启用了ssl,则发送和接收数据在ngx_ssl_recv ngx_ssl_write ngx_ssl_recv_chain ngx_ssl_send_chain */
     //以ngx_chain_t链表为参数来接收网络字符流的方法  ngx_recv_chain
     ngx_recv_chain_pt   recv_chain;  //赋值见ngx_event_accept     ngx_event_pipe_read_upstream中执行
     //以ngx_chain_t链表为参数来发送网络字符流的方法    ngx_send_chain
+    //当http2头部帧发送的时候，会在ngx_http_v2_header_filter把ngx_http_v2_send_chain.send_chain=ngx_http_v2_send_chain
     ngx_send_chain_pt   send_chain; //赋值见ngx_event_accept   ngx_http_write_filter和ngx_chain_writer中执行
 
     //这个连接对应的ngx_listening_t监听对象,通过listen配置项配置，此连接由listening监听端口的事件建立,赋值在ngx_event_process_init

nginx-1.9.2/src/core/ngx_connection.h

@@ -1531,6 +1531,7 @@ name=Professional%20Ajax&publisher=Wiley
     //如果后端带有Transfer-Encoding: chunked会置1
     unsigned                          chunked:1; //chunk编码方式组包实际组包过程参考ngx_http_chunked_body_filter
     //当下游的r->method == NGX_HTTP_HEAD请求方法只请求头部行，则会在ngx_http_header_filter中置1
+    //HTTP2头部帧发送在ngx_http_v2_header_filter中置1
     unsigned                          header_only:1; //表示是否只有行、头部，没有包体  ngx_http_header_filter中置1
     //在1.0以上版本默认是长连接，1.0以上版本默认置1，如果在请求头里面没有设置连接方式，见ngx_http_handler
     //标志位，为1时表示当前请求是keepalive请求  1长连接   0短连接  长连接时间通过请求头部的Keep-Alive:设置，参考ngx_http_headers_in_t

nginx-1.9.2/src/http/ngx_http_request.h

@@ -495,6 +495,7 @@ ngx_http_v2_send_output_queue(ngx_http_v2_connection_t *h2c)
                        out->blocked, out->length);
     }
 
+    /* 如果启用了ssl,则发送和接收数据在ngx_ssl_recv ngx_ssl_write ngx_ssl_recv_chain ngx_ssl_send_chain */
     cl = c->send_chain(c, cl, 0);
 
     if (cl == NGX_CHAIN_ERROR) {
@@ -577,6 +578,7 @@ ngx_http_v2_send_output_queue(ngx_http_v2_connection_t *h2c)
         frame = out;
     }
 
+    /*  */
     h2c->last_out = frame;
 
     return NGX_OK;
@@ -1321,6 +1323,8 @@ ngx_http_v2_state_header_block(ngx_http_v2_connection_t *h2c, u_char *pos,
         | Value String (Length octets)  |
         +-------------------------------+
         */
+        
+    /* NGINX在ngx_http_v2_state_header_block对接收到的头部帧进行解码解包，在ngx_http_v2_header_filter中对头部帧进行编码组包 */
     if (ch >= (1 << 7)) { /* 128 ~ 256的时候prefix为bit:0111 1111 */
         //在预定的头字段静态映射表 中已经有预定义的 Header Name 和 Header Value值
         /* indexed header field */ //说明索引表中已经存在该请求行信息，见ngx_http_v2_static_table
@@ -1347,8 +1351,9 @@ ngx_http_v2_state_header_block(ngx_http_v2_connection_t *h2c, u_char *pos,
         prefix = ngx_http_v2_prefix(3);
     }
 
+    //这里的value索引解码过程和ngx_http_v2_indexed对应
     value = ngx_http_v2_parse_int(h2c, &pos, end, prefix);
-
+    
     if (value < 0) {
         if (value == NGX_AGAIN) {
             return ngx_http_v2_state_save(h2c, pos, end,
@@ -2485,7 +2490,7 @@ ngx_http_v2_connection_error(ngx_http_v2_connection_t *h2c,
     return NULL;
 }
 
-
+//这里的index索引解码过程和ngx_http_v2_indexed对应
 static ngx_int_t
 ngx_http_v2_parse_int(ngx_http_v2_connection_t *h2c, u_char **pos, u_char *end,
     ngx_uint_t prefix)

nginx-1.9.2/src/http/v2/ngx_http_v2.c

@@ -526,7 +526,7 @@ typedef struct {
     /* 如果收到的value不在压缩表中，需要直接从报文读取，见ngx_http_v2_state_header_block ngx_http_v2_state_process_header */
     unsigned                         parse_value:1;
     /* ngx_http_v2_state_header_block中置1，表示需要把name:value通过ngx_http_v2_add_header加入动态表中，然后置0 */
-    unsigned                         index:1; //需要添加name:value到动态表中
+    unsigned                         index:1; //需要添加name:value到映射表中
     ngx_http_v2_header_t             header; //赋值见ngx_http_v2_get_indexed_header
     /* header内容中的所有name+value之和长度最大值，生效见ngx_http_v2_state_process_header 
     限制经过HPACK压缩后完整请求头的最大尺寸。
@@ -594,7 +594,8 @@ struct ngx_http_v2_connection_s {
 
     /* ngx_http_v2_create_stream中自增，表示创建的流的数量，ngx_http_v2_close_stream自减 */
     ngx_uint_t                       processing;
-
+    
+    /* 注意ngx_http_v2_connection_s的send_window、recv_window、init_window与ngx_http_v2_stream_s的send_window、recv_window的区别 */
     size_t                           send_window;//默认NGX_HTTP_V2_DEFAULT_WINDOW
     size_t                           recv_window;//默认NGX_HTTP_V2_MAX_WINDOW
     // 接收到对端的setting帧后，会做调整，见ngx_http_v2_state_settings_params
@@ -665,14 +666,16 @@ struct ngx_http_v2_stream_s {
     ngx_http_v2_node_t              *node;
 
     ngx_uint_t                       header_buffers;
+    //1表示数据已经入队，还没有发送，在ngx_http_v2_finalize_connection清0
     ngx_uint_t                       queued;
 
     /*
      * A change to SETTINGS_INITIAL_WINDOW_SIZE could cause the
      * send_window to become negative, hence it's signed.
      */
-    ssize_t                          send_window;
-    size_t                           recv_window;
+    /* 注意ngx_http_v2_connection_s的send_window、recv_window、init_window与ngx_http_v2_stream_s的send_window、recv_window的区别 */
+    ssize_t                          send_window; //默认值NGX_HTTP_V2_DEFAULT_WINDOW
+    size_t                           recv_window; //默认值NGX_HTTP_V2_MAX_WINDOW
 
     ngx_http_v2_out_frame_t         *free_frames;
     ngx_chain_t                     *free_data_headers;

nginx-1.9.2/src/http/v2/ngx_http_v2.h

@@ -11,16 +11,17 @@
 #include <nginx.h>
 #include <ngx_http_v2_module.h>
 
-
+//这里的ngx_http_v2_integer_octets ngx_http_v2_integer_octets index索引编码过程和ngx_http_v2_state_header_block中的解码过程对应
+//ngx_http_v2_integer_octets ngx_http_v2_indexed进行整数编码，ngx_http_v2_literal_size进行字符串编码
 #define ngx_http_v2_integer_octets(v)  (((v) + 127) / 128)
-
 #define ngx_http_v2_literal_size(h)                                           \
     (ngx_http_v2_integer_octets(sizeof(h) - 1) + sizeof(h) - 1)
 
+/* 128也就是位操作1000 0000,也就是该index在索引表中，如果i为1表示索引表的0，i=2对应索引表的1，i=3对应索引表的2，i=4对应索引表的3 */
 #define ngx_http_v2_indexed(i)      (128 + (i))
 #define ngx_http_v2_inc_indexed(i)  (64 + (i))
 
-
+/* 和ngx_http_v2_static_table数组下表对应，相差1 */
 #define NGX_HTTP_V2_STATUS_INDEX          8
 #define NGX_HTTP_V2_STATUS_200_INDEX      8
 #define NGX_HTTP_V2_STATUS_204_INDEX      9
@@ -230,7 +231,9 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
         }
     }
 
-    /* NGINX在ngx_http_v2_state_header_block对接收到的头部帧进行解码解包，在ngx_http_v2_header_filter中对头部帧进行编码组包 */
+    /* NGINX在ngx_http_v2_state_header_block对接收到的头部帧进行解码解包，在ngx_http_v2_header_filter中对头部帧进行编码组包
+       静态映射表在ngx_http_v2_static_table
+    */
 
     /* 头部9字节 + status响应长度(1字节为什么可以表示status响应码，因为一个字节就可以表示静态表的那个成员,见ngx_http_v2_static_table) */
     len = NGX_HTTP_V2_FRAME_HEADER_SIZE
@@ -379,6 +382,7 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
     part = &r->headers_out.headers.part;
     header = part->elts;
 
+    /* header_out数组列表中的所有NAME:VALUE长度加进来 */
     for (i = 0; /* void */; i++) {
 
         if (i >= part->nelts) {
@@ -415,6 +419,7 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
 
     stream = r->stream;
 
+    /* 如果整个头部帧内容超过了最大frame_size大小，则可能需要拆分到多个帧 */
     len += NGX_HTTP_V2_FRAME_HEADER_SIZE
            * (len / stream->connection->frame_size);
 
@@ -429,7 +434,6 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
 
     if (status) {
         *b->last++ = status;
-
     } else {
         *b->last++ = ngx_http_v2_inc_indexed(NGX_HTTP_V2_STATUS_INDEX);
         *b->last++ = 3;
@@ -617,13 +621,15 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
     cl->buf = b;
     cl->next = NULL;
 
+    /* 针对前面的header帧封包，组一个frame结构，挂到h2c->last_out队列，通过ngx_http_v2_filter_send触发发送出去 */
     frame = ngx_palloc(r->pool, sizeof(ngx_http_v2_out_frame_t));
     if (frame == NULL) {
         return NGX_ERROR;
     }
 
     frame->first = cl;
     frame->last = cl;
+    //该frame上对应的数据发送完毕后，会调用ngx_http_v2_headers_frame_handler
     frame->handler = ngx_http_v2_headers_frame_handler;
     frame->stream = stream;
     frame->length = b->last - b->pos - NGX_HTTP_V2_FRAME_HEADER_SIZE;
@@ -641,11 +647,14 @@ ngx_http_v2_header_filter(ngx_http_request_t *r)
         return NGX_ERROR;
     }
 
+    
     cln->handler = ngx_http_v2_filter_cleanup;
     cln->data = stream;
 
     stream->queued = 1;
 
+    //把ngx_http_v2_send_chain.send_chain=ngx_http_v2_header_filter,后面的数据帧就通过该函数发送，
+    //在读取到后端数据后开始走out filter流程，然后调用ngx_http_output_filter，最终执行该ngx_http_v2_send_chain
     fc->send_chain = ngx_http_v2_send_chain;
     fc->need_last_buf = 1;
 
@@ -711,7 +720,12 @@ ngx_http_v2_write_continuation_head(u_char *pos, size_t length, ngx_uint_t sid,
     (void) ngx_http_v2_write_sid(pos, sid);
 }
 
+/*
+当http2头部帧发送的时候，会在ngx_http_v2_header_filter把ngx_http_v2_send_chain.send_chain=ngx_http_v2_send_chain
 
+该函数发送数据帧
+在读取到后端数据后开始走out filter流程，然后调用ngx_http_output_filter，最终执行该ngx_http_v2_send_chain
+*/
 static ngx_chain_t *
 ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
 {
@@ -726,6 +740,8 @@ ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
 
     r = fc->data;
     stream = r->stream;
+    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
+                   "ngx_http_v2_send_chain");
 
 #if (NGX_SUPPRESS_WARN)
     size = 0;
@@ -741,7 +757,7 @@ ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
         in = in->next;
     }
 
-    if (in == NULL) {
+    if (in == NULL) { /* chain链上没有要发送的数据 */
 
         if (stream->queued) {
             fc->write->delayed = 1;
@@ -754,6 +770,7 @@ ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
 
     h2c = stream->connection;
 
+    /* 窗口 */
     if (size && ngx_http_v2_flow_control(h2c, stream) == NGX_DECLINED) {
         fc->write->delayed = 1;
         return in;
@@ -779,31 +796,33 @@ ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
         offset = 0;
     }
 
+    /* 发送limit不能超过h2c->send_window和stream->send_window的最小值 */
     if (limit == 0 || limit > (off_t) h2c->send_window) {
         limit = h2c->send_window;
     }
-
     if (limit > stream->send_window) {
         limit = (stream->send_window > 0) ? stream->send_window : 0;
     }
 
     h2lcf = ngx_http_get_module_loc_conf(r, ngx_http_v2_module);
 
+    /* frame_size为本地配置chunk_size和对端通知的frame_size的最小值 */
     frame_size = (h2lcf->chunk_size < h2c->frame_size)
                  ? h2lcf->chunk_size : h2c->frame_size;
 
 #if (NGX_SUPPRESS_WARN)
     cl = NULL;
 #endif
 
-    for ( ;; ) {
+    for ( ;; ) {  
         if ((off_t) frame_size > limit) {
             frame_size = (size_t) limit;
         }
 
         ln = &out;
         rest = frame_size;
 
+        /* 把chain链中的buf组包到新的cl chain(即out链)链中,但是数据总大小不能超过rest限制 */
         while ((off_t) rest >= size) {
 
             if (offset) {
@@ -831,8 +850,8 @@ ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
             in = in->next;
 
             if (in == NULL) {
-                frame_size -= rest;
-                rest = 0;
+                frame_size -= rest; //in链中的数据已经全部移到out链，这时候的frame_size就是out中的数据大小
+                rest = 0; //清0，说明所有的in链中的数据都可以全部发送出去
                 break;
             }
 
@@ -861,6 +880,7 @@ ngx_http_v2_send_chain(ngx_connection_t *fc, ngx_chain_t *in, off_t limit)
 
         ngx_http_v2_queue_frame(h2c, frame);
 
+        /* 发送了这么多数据，则窗口减少 */
         h2c->send_window -= frame_size;
 
         stream->send_window -= frame_size;
@@ -931,7 +951,7 @@ ngx_http_v2_filter_get_shadow(ngx_http_v2_stream_t *stream, ngx_buf_t *buf,
     return cl;
 }
 
-
+//获取data帧frame结构
 static ngx_http_v2_out_frame_t *
 ngx_http_v2_filter_get_data_frame(ngx_http_v2_stream_t *stream,
     size_t len, ngx_chain_t *first, ngx_chain_t *last)
@@ -1031,7 +1051,7 @@ ngx_http_v2_filter_send(ngx_connection_t *fc, ngx_http_v2_stream_t *stream)
     return NGX_OK;
 }
 
-
+/* 查看发送窗口是不是大于0，大于0则发送 */
 static ngx_inline ngx_int_t
 ngx_http_v2_flow_control(ngx_http_v2_connection_t *h2c,
     ngx_http_v2_stream_t *stream)