菜鸟学习Nginx之HTTP会话

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菜鸟学习Nginx之HTTP会话

从本篇开始，介绍Nginx中HTTP相关。Nginx做为Web Server那么HTTP必然是重中之重。本篇不打算介绍太深入，本篇最主要内容是如何与事件驱动关联起来。

一、监听端口

Nginx默认监听端口是80端口，那么Nginx是如何将80端口的listening事件注册到事件驱动（epoll）中呢？这里简单回顾一下，具体内容可参考《菜鸟学习nginx之核心模块ngx_events_module》。

worker进程的进程主函数是ngx_worker_process_cycle。进入该函数会先调用函数ngx_worker_process_init进行初始化流程，当ngx_worker_process_init返回之后则进入无限循环即投入服务。那么在ngx_worker_process_init函数就会把listening socket加入到事件驱动epoll中。然而真正加入到epoll对象中是函数ngx_event_process_init函数，部分代码如下：

    /*** for each listening socket * 循环遍历listening 将listen socket 与connection对象进行绑定*/ls = cycle->listening.elts;for (i = 0; i < cycle-<s; i++){#if (NGX_HAVE_REUSEPORT)if (ls[i].reuseport && ls[i].worker != ngx_worker){continue;}
#endif/* 返回可用连接对象 这里listening socket也会占用一个connection对象 */c = ngx_get_connection(ls[i].fd, cycle->log);if (c == NULL){return NGX_ERROR;}c->type = ls[i].type;c->log = &ls[i].log;c->listening = &ls[i];ls[i].connection = c;rev = c->read;rev->log = c->log;rev->accept = 1; /* 表示当前读事件是accept事件 用于区别正常数据报文读取还是Accept事件读取 */#if (NGX_HAVE_DEFERRED_ACCEPT)rev->deferred_accept = ls[i].deferred_accept;
#endifif (!(ngx_event_flags & NGX_USE_IOCP_EVENT)){if (ls[i].previous){/** delete the old accept events that were bound to* the old cycle read events array*/old = ls[i].previous->connection;if (ngx_del_event(old->read, NGX_READ_EVENT, NGX_CLOSE_EVENT) == NGX_ERROR){return NGX_ERROR;}old->fd = (ngx_socket_t)-1;}}#if (NGX_WIN32)...#elserev->handler = (c->type == SOCK_STREAM) ? ngx_event_accept: ngx_event_recvmsg;#if (NGX_HAVE_REUSEPORT)if (ls[i].reuseport){if (ngx_add_event(rev, NGX_READ_EVENT, 0) == NGX_ERROR){return NGX_ERROR;}continue;}#endifif (ngx_use_accept_mutex){continue;}//注册读事件 主要是用于listen监听if (ngx_add_event(rev, NGX_READ_EVENT, 0) == NGX_ERROR){return NGX_ERROR;}#endif}

循环遍历listenings数组，通过ngx_add_event函数，逐个将listening socket加入到epoll对象中且设置事件类型为READ事件。

至此Nginx完成了listening socket注册到epoll事件驱动中。当客户端发来请求时就会调用回调函数--ngx_event_accept。

二、Accept事件

注册listening socket到epoll的流程中有这样一行代码，用于设置回调函数，具体如下：

/* TCP连接的回调函数是ngx_event_accept，其他的回调函数则是ngx_event_recv_msg */
rev->handler = (c->type == SOCK_STREAM) ? ngx_event_accept: ngx_event_recvmsg;

这里使用的协议是TCP，所以当客户端的连接请求到来时，会触发回调函数ngx_event_accept函数执行，具体如何执行可参考《菜鸟学习nginx之事件模块epoll（1）》。

2.1、流程图

从流程图中可以看出，这部分代码逻辑还是比较繁琐，下面我们分片进行分析解读。

2.2、超时处理

/*** 处理Accept事件* @param ev 待读事件*/
void
ngx_event_accept(ngx_event_t *ev)
{socklen_t          socklen;ngx_err_t          err;ngx_log_t         *log;ngx_uint_t         level;ngx_socket_t       s;ngx_event_t       *rev, *wev;ngx_sockaddr_t     sa;ngx_listening_t   *ls;ngx_connection_t  *c, *lc;ngx_event_conf_t  *ecf;
#if (NGX_HAVE_ACCEPT4)static ngx_uint_t  use_accept4 = 1;
#endifif (ev->timedout) {//表示超时 重新添加listen socket到事件驱动中if (ngx_enable_accept_events((ngx_cycle_t *) ngx_cycle) != NGX_OK) {return;}ev->timedout = 0;}//获取event配置项ecf = ngx_event_get_conf(ngx_cycle->conf_ctx, ngx_event_core_module);if (!(ngx_event_flags & NGX_USE_KQUEUE_EVENT)) {ev->available = ecf->multi_accept;}//从用户私有数据中获取当前事件所对应的connection以及listening对象lc = ev->data;ls = lc->listening;ev->ready = 0;ngx_log_debug2(NGX_LOG_DEBUG_EVENT, ev->log, 0,"accept on %V, ready: %d", &ls->addr_text, ev->available);

这代码主要用于判断当前事件是否为超时事件。超时事件的产生条件是在定时器周期内没有新的请求到来，此时需要重新注册listening socket到epoll中。下面进入主流程do while循环。

2.3、调用accept接收用户请求

    do {socklen = sizeof(ngx_sockaddr_t);/* 接收客户端连接建立请求 */
#if (NGX_HAVE_ACCEPT4)if (use_accept4) {s = accept4(lc->fd, &sa.sockaddr, &socklen, SOCK_NONBLOCK);//默认创建的socket是非阻塞socket} else {s = accept(lc->fd, &sa.sockaddr, &socklen);}
#elses = accept(lc->fd, &sa.sockaddr, &socklen);
#endif/* 连接建立失败 */if (s == (ngx_socket_t) -1) {err = ngx_socket_errno;if (err == NGX_EAGAIN) {ngx_log_debug0(NGX_LOG_DEBUG_EVENT, ev->log, err,"accept() not ready");return;}level = NGX_LOG_ALERT;if (err == NGX_ECONNABORTED) {level = NGX_LOG_ERR;} else if (err == NGX_EMFILE || err == NGX_ENFILE) {level = NGX_LOG_CRIT;}#if (NGX_HAVE_ACCEPT4)ngx_log_error(level, ev->log, err,use_accept4 ? "accept4() failed" : "accept() failed");if (use_accept4 && err == NGX_ENOSYS) {use_accept4 = 0;ngx_inherited_nonblocking = 0;//尝试用accept接口处理新请求continue;}
#elsengx_log_error(level, ev->log, err, "accept() failed");
#endifif (err == NGX_ECONNABORTED) {if (ngx_event_flags & NGX_USE_KQUEUE_EVENT) {ev->available--;}if (ev->available) {continue;}}if (err == NGX_EMFILE || err == NGX_ENFILE) {if (ngx_disable_accept_events((ngx_cycle_t *) ngx_cycle, 1)!= NGX_OK){return;}if (ngx_use_accept_mutex) {if (ngx_accept_mutex_held) {ngx_shmtx_unlock(&ngx_accept_mutex);ngx_accept_mutex_held = 0;}ngx_accept_disabled = 1;} else {ngx_add_timer(ev, ecf->accept_mutex_delay);}}return;}

根据不同的错误码，进行特殊处理，大部分场景最后都是return操作。

2.4、创建connection对象

当accept返回成功，则表新的tcp连接已经建立成功，Nginx需要对其进行封装成connection对象并对connection结构成员进行初始化操作，例如socket操作设置等，具体代码如下：

        /* 负数 负载均衡*/       ngx_accept_disabled = ngx_cycle->connection_n / 8- ngx_cycle->free_connection_n;c = ngx_get_connection(s, ev->log);//获取新的connection对象if (c == NULL) {if (ngx_close_socket(s) == -1) {ngx_log_error(NGX_LOG_ALERT, ev->log, ngx_socket_errno,ngx_close_socket_n " failed");}return;}c->type = SOCK_STREAM;#if (NGX_STAT_STUB)(void) ngx_atomic_fetch_add(ngx_stat_active, 1);
#endif/* 创建连接级内存池 */c->pool = ngx_create_pool(ls->pool_size, ev->log);if (c->pool == NULL) {ngx_close_accepted_connection(c);return;}if (socklen > (socklen_t) sizeof(ngx_sockaddr_t)) {socklen = sizeof(ngx_sockaddr_t);}c->sockaddr = ngx_palloc(c->pool, socklen);if (c->sockaddr == NULL) {ngx_close_accepted_connection(c);return;}ngx_memcpy(c->sockaddr, &sa, socklen);log = ngx_palloc(c->pool, sizeof(ngx_log_t));if (log == NULL) {ngx_close_accepted_connection(c);return;}/* set a blocking mode for iocp and non-blocking mode for others */if (ngx_inherited_nonblocking) {if (ngx_event_flags & NGX_USE_IOCP_EVENT) {if (ngx_blocking(s) == -1) {ngx_log_error(NGX_LOG_ALERT, ev->log, ngx_socket_errno,ngx_blocking_n " failed");ngx_close_accepted_connection(c);return;}}} else {if (!(ngx_event_flags & NGX_USE_IOCP_EVENT)) {if (ngx_nonblocking(s) == -1) {ngx_log_error(NGX_LOG_ALERT, ev->log, ngx_socket_errno,ngx_nonblocking_n " failed");ngx_close_accepted_connection(c);return;}}}*log = ls->log;/* 初始化connection对象 参考ngx_linux_io */c->recv = ngx_recv;c->send = ngx_send;c->recv_chain = ngx_recv_chain;c->send_chain = ngx_send_chain;c->log = log;c->pool->log = log;c->socklen = socklen;c->listening = ls;c->local_sockaddr = ls->sockaddr;c->local_socklen = ls->socklen;#if (NGX_HAVE_UNIX_DOMAIN)if (c->sockaddr->sa_family == AF_UNIX) {c->tcp_nopush = NGX_TCP_NOPUSH_DISABLED;c->tcp_nodelay = NGX_TCP_NODELAY_DISABLED;
#if (NGX_SOLARIS)/* Solaris's sendfilev() supports AF_NCA, AF_INET, and AF_INET6 */c->sendfile = 0;
#endif}
#endifrev = c->read;wev = c->write;wev->ready = 1;if (ngx_event_flags & NGX_USE_IOCP_EVENT) {rev->ready = 1;}if (ev->deferred_accept) {rev->ready = 1;
#if (NGX_HAVE_KQUEUE || NGX_HAVE_EPOLLRDHUP)rev->available = 1;
#endif}rev->log = log;wev->log = log;/** TODO: MT: - ngx_atomic_fetch_add()*             or protection by critical section or light mutex** TODO: MP: - allocated in a shared memory*           - ngx_atomic_fetch_add()*             or protection by critical section or light mutex*/c->number = ngx_atomic_fetch_add(ngx_connection_counter, 1);#if (NGX_STAT_STUB)(void) ngx_atomic_fetch_add(ngx_stat_handled, 1);
#endifif (ls->addr_ntop) {c->addr_text.data = ngx_pnalloc(c->pool, ls->addr_text_max_len);if (c->addr_text.data == NULL) {ngx_close_accepted_connection(c);return;}c->addr_text.len = ngx_sock_ntop(c->sockaddr, c->socklen,c->addr_text.data,ls->addr_text_max_len, 0);if (c->addr_text.len == 0) {ngx_close_accepted_connection(c);return;}}

2.5、HTTP框架初始化connection对象

下面这段代码最主要功能是对connection对象初始化流程，如下：

        /*** ngx_add_conn不空且没有设置NGX_USE_EPOLL_EVENT标志位 * epoll模型不会进入此分支*/if (ngx_add_conn && (ngx_event_flags & NGX_USE_EPOLL_EVENT) == 0) {if (ngx_add_conn(c) == NGX_ERROR) {ngx_close_accepted_connection(c);return;}}log->data = NULL;log->handler = NULL;/** 此回调函数用于处理新的连接 handler赋值由HTTP框架设置* ngx_http_init_connection 这个函数主要功能是将当前socket注册到事件驱动中*/ls->handler(c);if (ngx_event_flags & NGX_USE_KQUEUE_EVENT) {ev->available--;}} while (ev->available);

三、注册事件驱动

上面章节，Nginx是如何处理Accept事件，但是有一点疑问是accept函数返回的socket是如何加入到epoll中呢？listening socket是如何再次加入到epoll中呢（每次accept事件之后需要重新加入）?

3.1、新socket加入epoll事件驱动

在上一节中有这一行代码：

        /** 此回调函数用于处理新的连接 handler赋值由HTTP框架设置* ngx_http_init_connection 这个函数主要功能是将当前socket注册到事件驱动中*/ls->handler(c);

该代码是HTTP框架用于初始化连接，回调函数是ngx_http_init_connection，该函数用于将客户端与服务端通信的socket加入到事件驱动中：

/*** 初始化http连接* @param c TCP连接*/
void ngx_http_init_connection(ngx_connection_t *c)
{ngx_uint_t i;ngx_event_t *rev;struct sockaddr_in *sin;ngx_http_port_t *port;ngx_http_in_addr_t *addr;ngx_http_log_ctx_t *ctx;ngx_http_connection_t *hc;
#if (NGX_HAVE_INET6)struct sockaddr_in6 *sin6;ngx_http_in6_addr_t *addr6;
#endif/* 在内存池中申请http connection对象 */hc = ngx_pcalloc(c->pool, sizeof(ngx_http_connection_t));if (hc == NULL){ngx_http_close_connection(c);return;}c->data = hc;//save /* find the server configuration for the address:port */port = c->listening->servers;/* 获取监听地址 如果有多个地址 则循环遍历 */if (port->naddrs > 1){/** there are several addresses on this port and one of them* is an "*:port" wildcard so getsockname() in ngx_http_server_addr()* is required to determine a server address*/if (ngx_connection_local_sockaddr(c, NULL, 0) != NGX_OK){ngx_http_close_connection(c);return;}switch (c->local_sockaddr->sa_family){#if (NGX_HAVE_INET6)case AF_INET6:sin6 = (struct sockaddr_in6 *)c->local_sockaddr;addr6 = port->addrs;/* the last address is "*" */for (i = 0; i < port->naddrs - 1; i++){if (ngx_memcmp(&addr6[i].addr6, &sin6->sin6_addr, 16) == 0){break;}}hc->addr_conf = &addr6[i].conf;break;
#endifdefault: /* AF_INET */sin = (struct sockaddr_in *)c->local_sockaddr;addr = port->addrs;/* the last address is "*" */for (i = 0; i < port->naddrs - 1; i++){if (addr[i].addr == sin->sin_addr.s_addr){break;}}hc->addr_conf = &addr[i].conf;break;}}else{switch (c->local_sockaddr->sa_family){#if (NGX_HAVE_INET6)case AF_INET6:addr6 = port->addrs;hc->addr_conf = &addr6[0].conf;break;
#endifdefault: /* AF_INET */addr = port->addrs;hc->addr_conf = &addr[0].conf;break;}}/* the default server configuration for the address:port */hc->conf_ctx = hc->addr_conf->default_server->ctx;ctx = ngx_palloc(c->pool, sizeof(ngx_http_log_ctx_t));if (ctx == NULL){ngx_http_close_connection(c);return;}ctx->connection = c;ctx->request = NULL;ctx->current_request = NULL;c->log->connection = c->number;c->log->handler = ngx_http_log_error;c->log->data = ctx;c->log->action = "waiting for request";c->log_error = NGX_ERROR_INFO;/* 设置读写事件handler回调函数 */rev = c->read;rev->handler = ngx_http_wait_request_handler; /* 读事件回调函数 */c->write->handler = ngx_http_empty_handler; /* 写事件回调函数 再未收到client请求不会主动发送数据 */#if (NGX_HTTP_V2)if (hc->addr_conf->http2){rev->handler = ngx_http_v2_init;}
#endif#if (NGX_HTTP_SSL){ngx_http_ssl_srv_conf_t *sscf;sscf = ngx_http_get_module_srv_conf(hc->conf_ctx, ngx_http_ssl_module);if (sscf->enable || hc->addr_conf->ssl){c->log->action = "SSL handshaking";if (hc->addr_conf->ssl && sscf-& == NULL){ngx_log_error(NGX_LOG_ERR, c->log, 0,"no "ssl_certificate" is defined ""in server listening on SSL port");ngx_http_close_connection(c);return;}hc->ssl = 1;rev->handler = ngx_http_ssl_handshake;}}
#endifif (hc->addr_conf->proxy_protocol){hc->proxy_protocol = 1;c->log->action = "reading PROXY protocol";}if (rev->ready){/* the deferred accept(), iocp */if (ngx_use_accept_mutex){ngx_post_event(rev, &ngx_posted_events);return;}rev->handler(rev);return;}/** 将事件添加到定时器和epoll事件驱动中* 回调函数都是ngx_http_wait_request_handler*/ngx_add_timer(rev, c->listening->post_accept_timeout);ngx_reusable_connection(c, 1);if (ngx_handle_read_event(rev, 0) != NGX_OK){ngx_http_close_connection(c);return;}
}

通过上述代码可知：

1、读事件处理函数为ngx_http_wait_request_handler，写事件处理函数为ngx_http_empty_handler。

2、将当前socket加入到epoll以及定时器中。