Nginx(三):http模块的处理流程解析之正向代理

  无疑,在nginx的核心服务中,http服务占据了相当大的份量。那么,要想多了解nginx多一点,则必须要了解其http模块的工作机制。

  而在上一篇文章中,我们已完全了解了nginx的worker工作机制,以及它是如何接入http服务的,但很明显那很粗,我们需要更深入点理解http模块的工作原理。

  而本身nginx对模块的支持又是复杂的,至少我们认为有两个大方向,正向代理和反向代理。正向代理实际上就是一个http服务器,明显简单些,所以,我们本篇就来说说nginx的正向代理实现吧。

 

0. 整体时序图

  如果你对nginx的http模块工作原理有过深入理解,相信只需要这一张时序图就够。为了节省大家宝贵时,可以先一览宏图。

 

1. 异步io事件的交接

  我们知道,nginx的核心是事件io机制的使用,当外部网络io就绪时,内核会回应nginx, 而nginx则会通过accept(), receive(), fd_set 等方法,将事件接入进来,从而转交到http服务模块。其中select模块我们上一篇中已经讲过,此时再简单回顾下:(需要的话)

// event/modules/ngx_select_module.c
// io 事件监听
static ngx_int_t
ngx_select_process_events(ngx_cycle_t *cycle, ngx_msec_t timer,
    ngx_uint_t flags) {
    int                ready, nready;
    ngx_err_t          err;
    ngx_uint_t         i, found;
    ngx_event_t       *ev;
    ngx_queue_t       *queue;
    struct timeval     tv, *tp;
    ngx_connection_t  *c;
    // 获取 max_fd, 系统传值需要
    if (max_fd == -1) {
        for (i = 0; i < nevents; i++) {
            c = event_index[i]->data;
            if (max_fd < c->fd) {
                max_fd = c->fd;
            }
        }

        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                       "change max_fd: %i", max_fd);
    }

#if (NGX_DEBUG)
    if (cycle->log->log_level & NGX_LOG_DEBUG_ALL) {
        for (i = 0; i < nevents; i++) {
            ev = event_index[i];
            c = ev->data;
            ngx_log_debug2(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                           "select event: fd:%d wr:%d", c->fd, ev->write);
        }

        ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                       "max_fd: %i", max_fd);
    }
#endif

    if (timer == NGX_TIMER_INFINITE) {
        tp = NULL;

    } else {
        tv.tv_sec = (long) (timer / 1000);
        tv.tv_usec = (long) ((timer % 1000) * 1000);
        tp = &tv;
    }

    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                   "select timer: %M", timer);

    work_read_fd_set = master_read_fd_set;
    work_write_fd_set = master_write_fd_set;
    // 在此处交由内核进行处理网络事件,epoll 机制,至少有一个事件到来时返回
    // tp 代表是否要超时退出
    ready = select(max_fd + 1, &work_read_fd_set, &work_write_fd_set, NULL, tp);

    err = (ready == -1) ? ngx_errno : 0;

    if (flags & NGX_UPDATE_TIME || ngx_event_timer_alarm) {
        // 事件结束后,先尝试更新gmtTime 时间信息
        ngx_time_update();
    }

    ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                   "select ready %d", ready);

    if (err) {
        ngx_uint_t  level;

        if (err == NGX_EINTR) {

            if (ngx_event_timer_alarm) {
                ngx_event_timer_alarm = 0;
                return NGX_OK;
            }

            level = NGX_LOG_INFO;

        } else {
            level = NGX_LOG_ALERT;
        }

        ngx_log_error(level, cycle->log, err, "select() failed");

        if (err == NGX_EBADF) {
            ngx_select_repair_fd_sets(cycle);
        }

        return NGX_ERROR;
    }

    if (ready == 0) {
        if (timer != NGX_TIMER_INFINITE) {
            return NGX_OK;
        }

        ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
                      "select() returned no events without timeout");
        return NGX_ERROR;
    }

    nready = 0;
    // 遍历所有事件
    for (i = 0; i < nevents; i++) {
        ev = event_index[i];
        c = ev->data;
        found = 0;
        // 写事件处理
        if (ev->write) {
            if (FD_ISSET(c->fd, &work_write_fd_set)) {
                found = 1;
                ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                               "select write %d", c->fd);
            }

        } 
        // 读或accept事件
        else {
            if (FD_ISSET(c->fd, &work_read_fd_set)) {
                found = 1;
                ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                               "select read %d", c->fd);
            }
        }
        // 读写就绪事件 found 都为1
        if (found) {
            ev->ready = 1;
            ev->available = -1;
            // 如果是 accept 事件则取 ngx_posted_accept_events 队列
            // 否则取 ngx_posted_events 队列
            queue = ev->accept ? &ngx_posted_accept_events
                               : &ngx_posted_events;
            // 将事件插入到相应队列尾部
            ngx_post_event(ev, queue);
            // 有效就绪事件+1
            nready++;
        }
    }
    // 如果两个值不相等,则需要修正下
    if (ready != nready) {
        ngx_log_error(NGX_LOG_ALERT, cycle->log, 0,
                      "select ready != events: %d:%d", ready, nready);

        ngx_select_repair_fd_sets(cycle);
    }

    return NGX_OK;
}
View Code

 

  反正大概意思就是会调用内核级别的select/poll或epoll等io机制,等待io事件的发生,然后返回到用户态。当然,为了保证系统例外情况,都会进行超时设置,避免系统事件检测的偶发异常,可以在超时机制帮助下正常工作。

  此处接收到的事件可能写入两个队列: 即是否是 accept 队列之分。最开始建立连接时,自然是放入accept队列的,后续则一般放ngx_posted_events队列中。这两个队列,后续将被分开处理。accept 队列会将socket接入,并注册read监听。而 posted_events 则是需要进行正式处理的队列,将会读取数据,写入客户端等更多工作。
其中,ngx_http_init_connection 的初始化过程,如需要请点击查看.

// http/ngx_http_request.c
// 初始化socket连接, 接入 http模块
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
    // 分配数据内存
    hc = ngx_pcalloc(c->pool, sizeof(ngx_http_connection_t));
    if (hc == NULL) {
        ngx_http_close_connection(c);
        return;
    }

    c->data = hc;

    /* find the server configuration for the address:port */

    port = c->listening->servers;

    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;
        }
        // 根据网络类型处理
        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;
#endif

        default: /* 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;
#endif

        default: /* 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;
    // 每个http server 都有自己的日志记录控制
    c->log->handler = ngx_http_log_error;
    c->log->data = ctx;
    c->log->action = "waiting for request";

    c->log_error = NGX_ERROR_INFO;

    rev = c->read;
    // 设置接收数据处理器为 ngx_http_wait_request_handler
    rev->handler = ngx_http_wait_request_handler;
    c->write->handler = ngx_http_empty_handler;

#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) {
        hc->ssl = 1;
        c->log->action = "SSL handshaking";
        rev->handler = ngx_http_ssl_handshake;
    }
    }
#endif

    if (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rev 放入到 ngx_event_timer_rbtree 队列中, 红黑树实现
    ngx_add_timer(rev, c->listening->post_accept_timeout);
    // 重用 connection
    ngx_reusable_connection(c, 1);
    // 处理 读就绪事件,注册 read 监听
    if (ngx_handle_read_event(rev, 0) != NGX_OK) {
        ngx_http_close_connection(c);
        return;
    }
}
View Code

 

  经过 ngx_http_init_connection 之后,就注册了read事件, 该事件基本已就绪, 所以将会在下一次进行select操作时返回该事件, 即下一次worker巡检时触发 read. 而此时的handler则被设置为 ngx_http_wait_request_handler.

// http/ngx_http_request.c
// 处理socket读事件
static void
ngx_http_wait_request_handler(ngx_event_t *rev)
{
    u_char                    *p;
    size_t                     size;
    ssize_t                    n;
    ngx_buf_t                 *b;
    ngx_connection_t          *c;
    ngx_http_connection_t     *hc;
    ngx_http_core_srv_conf_t  *cscf;

    c = rev->data;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "http wait request handler");

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT, "client timed out");
        ngx_http_close_connection(c);
        return;
    }

    if (c->close) {
        ngx_http_close_connection(c);
        return;
    }

    hc = c->data;
    cscf = ngx_http_get_module_srv_conf(hc->conf_ctx, ngx_http_core_module);
    // 默认1024 缓冲大小
    size = cscf->client_header_buffer_size;

    b = c->buffer;
    // 首次接入时,创建初始空间
    if (b == NULL) {
        // 创建缓冲区接收http传过来的数据
        b = ngx_create_temp_buf(c->pool, size);
        if (b == NULL) {
            ngx_http_close_connection(c);
            return;
        }

        c->buffer = b;

    } else if (b->start == NULL) {
        // 缓冲冲填满,需要另外增加空间?
        b->start = ngx_palloc(c->pool, size);
        if (b->start == NULL) {
            ngx_http_close_connection(c);
            return;
        }

        b->pos = b->start;
        b->last = b->start;
        b->end = b->last + size;
    }
    // 接收数据
    n = c->recv(c, b->last, size);

    if (n == NGX_AGAIN) {

        if (!rev->timer_set) {
            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;
        }

        /*
         * We are trying to not hold c->buffer's memory for an idle connection.
         */
        // 如果还要等待更多数据,释放占有空间
        if (ngx_pfree(c->pool, b->start) == NGX_OK) {
            b->start = NULL;
        }

        return;
    }

    if (n == NGX_ERROR) {
        ngx_http_close_connection(c);
        return;
    }

    if (n == 0) {
        ngx_log_error(NGX_LOG_INFO, c->log, 0,
                      "client closed connection");
        ngx_http_close_connection(c);
        return;
    }

    b->last += n;
    // 如果配置了  proxy_pass (且匹配了模式),  则走代理逻辑
    if (hc->proxy_protocol) {
        hc->proxy_protocol = 0;

        p = ngx_proxy_protocol_read(c, b->pos, b->last);

        if (p == NULL) {
            ngx_http_close_connection(c);
            return;
        }

        b->pos = p;

        if (b->pos == b->last) {
            c->log->action = "waiting for request";
            b->pos = b->start;
            b->last = b->start;
            ngx_post_event(rev, &ngx_posted_events);
            return;
        }
    }

    c->log->action = "reading client request line";
    // 设置不可重用连接
    ngx_reusable_connection(c, 0);
    // 创建 http 连接请求, 分配内存空, 设置下一个 handler 等等
    c->data = ngx_http_create_request(c);
    if (c->data == NULL) {
        ngx_http_close_connection(c);
        return;
    }
    // 设置读取数据的处理器为 ngx_http_process_request_line, 以便下次使用
    rev->handler = ngx_http_process_request_line;
    ngx_http_process_request_line(rev);
}
View Code

  ngx_http_wait_request_handler 非常重要的一个任务就是接收客户端的传送数据,即调用 recv 方法处理数据, 使用缓冲区的方式进行读取, 默认缓冲区大小为 1024, 即实际是处理不了太多数据的. 最多读取1024字节, 然后正常情况下就进入到 ngx_http_process_request_line() 逻辑了. 也就是说, 剩下的数据会在接下再被读取, 而非一次性被读取完成. 其中, ngx_http_create_request 主要是为 body体分配内存空间.

 

// http/ngx_http_request.c
ngx_http_request_t *
ngx_http_create_request(ngx_connection_t *c)
{
    ngx_http_request_t        *r;
    ngx_http_log_ctx_t        *ctx;
    ngx_http_core_loc_conf_t  *clcf;
    // 重要: 分配请求的上下文信息
    r = ngx_http_alloc_request(c);
    if (r == NULL) {
        return NULL;
    }

    c->requests++;

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    ngx_set_connection_log(c, clcf->error_log);

    ctx = c->log->data;
    ctx->request = r;
    ctx->current_request = r;

#if (NGX_STAT_STUB)
    (void) ngx_atomic_fetch_add(ngx_stat_reading, 1);
    r->stat_reading = 1;
    (void) ngx_atomic_fetch_add(ngx_stat_requests, 1);
#endif

    return r;
}
View Code

 

// http/ngx_http_request.c
static ngx_http_request_t *
ngx_http_alloc_request(ngx_connection_t *c)
{
    ngx_pool_t                 *pool;
    ngx_time_t                 *tp;
    ngx_http_request_t         *r;
    ngx_http_connection_t      *hc;
    ngx_http_core_srv_conf_t   *cscf;
    ngx_http_core_main_conf_t  *cmcf;

    hc = c->data;

    cscf = ngx_http_get_module_srv_conf(hc->conf_ctx, ngx_http_core_module);

    pool = ngx_create_pool(cscf->request_pool_size, c->log);
    if (pool == NULL) {
        return NULL;
    }

    r = ngx_pcalloc(pool, sizeof(ngx_http_request_t));
    if (r == NULL) {
        ngx_destroy_pool(pool);
        return NULL;
    }

    r->pool = pool;

    r->http_connection = hc;
    r->signature = NGX_HTTP_MODULE;
    r->connection = c;
    // 设置配置信息备用
    r->main_conf = hc->conf_ctx->main_conf;
    r->srv_conf = hc->conf_ctx->srv_conf;
    r->loc_conf = hc->conf_ctx->loc_conf;
    // 可能使用读取方式为 blocking, 如果是异步读取, 则无需blocking 
    r->read_event_handler = ngx_http_block_reading;
    // 将刚刚读取出的数据引用给到header指针, 以便重新读取
    r->header_in = hc->busy ? hc->busy->buf : c->buffer;

    if (ngx_list_init(&r->headers_out.headers, r->pool, 20,
                      sizeof(ngx_table_elt_t))
        != NGX_OK)
    {
        ngx_destroy_pool(r->pool);
        return NULL;
    }

    if (ngx_list_init(&r->headers_out.trailers, r->pool, 4,
                      sizeof(ngx_table_elt_t))
        != NGX_OK)
    {
        ngx_destroy_pool(r->pool);
        return NULL;
    }

    r->ctx = ngx_pcalloc(r->pool, sizeof(void *) * ngx_http_max_module);
    if (r->ctx == NULL) {
        ngx_destroy_pool(r->pool);
        return NULL;
    }

    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);

    r->variables = ngx_pcalloc(r->pool, cmcf->variables.nelts
                                        * sizeof(ngx_http_variable_value_t));
    if (r->variables == NULL) {
        ngx_destroy_pool(r->pool);
        return NULL;
    }

#if (NGX_HTTP_SSL)
    if (c->ssl) {
        r->main_filter_need_in_memory = 1;
    }
#endif

    r->main = r;
    r->count = 1;
    // 分配系统默认值
    tp = ngx_timeofday();
    r->start_sec = tp->sec;
    r->start_msec = tp->msec;

    r->method = NGX_HTTP_UNKNOWN;
    r->http_version = NGX_HTTP_VERSION_10;

    r->headers_in.content_length_n = -1;
    r->headers_in.keep_alive_n = -1;
    r->headers_out.content_length_n = -1;
    r->headers_out.last_modified_time = -1;

    r->uri_changes = NGX_HTTP_MAX_URI_CHANGES + 1;
    r->subrequests = NGX_HTTP_MAX_SUBREQUESTS + 1;

    r->http_state = NGX_HTTP_READING_REQUEST_STATE;

    r->log_handler = ngx_http_log_error_handler;

    return r;
}

  而接下来的handler被设置为了 ngx_http_process_request_line , 则会进一步读取数据, 处理事件, 也是处理的核心任务.

 

2. 核心数据读取解析

  前面我们看到, nginx 通过调用系统级recv() 接收部分客户端数据过来, 但那里仅有一个缓冲区的大小, 有可能取到的数据是不完整的. 那么, 自然需要进一步处理, 即: ngx_http_process_request_line .  它会在第一次接到数据时就进行调用, 但如果存在多数据段, 则会反复进行该 handler 的调用(这是一个核心的异步io的处理实现, 类似断点续传):

 

// http/ngx_http_request.c
// 读取body数据,并响应客户端
static void
ngx_http_process_request_line(ngx_event_t *rev)
{
    ssize_t              n;
    ngx_int_t            rc, rv;
    ngx_str_t            host;
    ngx_connection_t    *c;
    ngx_http_request_t  *r;

    c = rev->data;
    r = c->data;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, rev->log, 0,
                   "http process request line");

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT, "client timed out");
        c->timedout = 1;
        ngx_http_close_request(r, NGX_HTTP_REQUEST_TIME_OUT);
        return;
    }

    rc = NGX_AGAIN;

    for ( ;; ) {

        if (rc == NGX_AGAIN) {
            // 读取header, 因为前面已经读取了部分buff, 可能就直接返回
            n = ngx_http_read_request_header(r);

            if (n == NGX_AGAIN || n == NGX_ERROR) {
                break;
            }
        }
        // 读取body 数据, 按照http协议解析,非常长
        // 如解析出 GET HTTP1.1...
        rc = ngx_http_parse_request_line(r, r->header_in);

        if (rc == NGX_OK) {

            /* the request line has been parsed successfully */
            // 解析成功部分信息, 进行记录处理
            r->request_line.len = r->request_end - r->request_start;
            r->request_line.data = r->request_start;
            r->request_length = r->header_in->pos - r->request_start;

            ngx_log_debug1(NGX_LOG_DEBUG_HTTP, c->log, 0,
                           "http request line: \"%V\"", &r->request_line);

            r->method_name.len = r->method_end - r->request_start + 1;
            r->method_name.data = r->request_line.data;

            if (r->http_protocol.data) {
                r->http_protocol.len = r->request_end - r->http_protocol.data;
            }
            // 处理 uri, 解析路径, 放入 r->uri.data
            if (ngx_http_process_request_uri(r) != NGX_OK) {
                break;
            }

            if (r->schema_end) {
                r->schema.len = r->schema_end - r->schema_start;
                r->schema.data = r->schema_start;
            }

            if (r->host_end) {

                host.len = r->host_end - r->host_start;
                host.data = r->host_start;

                rc = ngx_http_validate_host(&host, r->pool, 0);

                if (rc == NGX_DECLINED) {
                    ngx_log_error(NGX_LOG_INFO, c->log, 0,
                                  "client sent invalid host in request line");
                    ngx_http_finalize_request(r, NGX_HTTP_BAD_REQUEST);
                    break;
                }

                if (rc == NGX_ERROR) {
                    ngx_http_close_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                    break;
                }

                if (ngx_http_set_virtual_server(r, &host) == NGX_ERROR) {
                    break;
                }

                r->headers_in.server = host;
            }

            if (r->http_version < NGX_HTTP_VERSION_10) {

                if (r->headers_in.server.len == 0
                    && ngx_http_set_virtual_server(r, &r->headers_in.server)
                       == NGX_ERROR)
                {
                    break;
                }

                ngx_http_process_request(r);
                break;
            }


            if (ngx_list_init(&r->headers_in.headers, r->pool, 20,
                              sizeof(ngx_table_elt_t))
                != NGX_OK)
            {
                ngx_http_close_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                break;
            }

            c->log->action = "reading client request headers";
            // 如果运行到此处, 则意味着header数据未读取完成, 需要下一次io事件继续
            // handler 变更为 ngx_http_process_request_headers
            rev->handler = ngx_http_process_request_headers;
            ngx_http_process_request_headers(rev);

            break;
        }

        if (rc != NGX_AGAIN) {

            /* there was error while a request line parsing */

            ngx_log_error(NGX_LOG_INFO, c->log, 0,
                          ngx_http_client_errors[rc - NGX_HTTP_CLIENT_ERROR]);

            if (rc == NGX_HTTP_PARSE_INVALID_VERSION) {
                ngx_http_finalize_request(r, NGX_HTTP_VERSION_NOT_SUPPORTED);

            } else {
                ngx_http_finalize_request(r, NGX_HTTP_BAD_REQUEST);
            }

            break;
        }

        /* NGX_AGAIN: a request line parsing is still incomplete */

        if (r->header_in->pos == r->header_in->end) {

            rv = ngx_http_alloc_large_header_buffer(r, 1);

            if (rv == NGX_ERROR) {
                ngx_http_close_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                break;
            }

            if (rv == NGX_DECLINED) {
                r->request_line.len = r->header_in->end - r->request_start;
                r->request_line.data = r->request_start;

                ngx_log_error(NGX_LOG_INFO, c->log, 0,
                              "client sent too long URI");
                ngx_http_finalize_request(r, NGX_HTTP_REQUEST_URI_TOO_LARGE);
                break;
            }
        }
    }
    // 处理请求, 响应客户端
    ngx_http_run_posted_requests(c);
}

    
// http/ngx_http_request.c
// 进一步处理 header 信息
static void
ngx_http_process_request_headers(ngx_event_t *rev)
{
    u_char                     *p;
    size_t                      len;
    ssize_t                     n;
    ngx_int_t                   rc, rv;
    ngx_table_elt_t            *h;
    ngx_connection_t           *c;
    ngx_http_header_t          *hh;
    ngx_http_request_t         *r;
    ngx_http_core_srv_conf_t   *cscf;
    ngx_http_core_main_conf_t  *cmcf;

    c = rev->data;
    r = c->data;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, rev->log, 0,
                   "http process request header line");

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT, "client timed out");
        c->timedout = 1;
        ngx_http_close_request(r, NGX_HTTP_REQUEST_TIME_OUT);
        return;
    }

    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);

    rc = NGX_AGAIN;

    for ( ;; ) {
        // 依次解析每一行 header 信息
        if (rc == NGX_AGAIN) {
            // 如果解析到最后还没完, 说明后续还需要读取数据
            if (r->header_in->pos == r->header_in->end) {

                rv = ngx_http_alloc_large_header_buffer(r, 0);

                if (rv == NGX_ERROR) {
                    ngx_http_close_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                    break;
                }

                if (rv == NGX_DECLINED) {
                    p = r->header_name_start;

                    r->lingering_close = 1;

                    if (p == NULL) {
                        ngx_log_error(NGX_LOG_INFO, c->log, 0,
                                      "client sent too large request");
                        ngx_http_finalize_request(r,
                                            NGX_HTTP_REQUEST_HEADER_TOO_LARGE);
                        break;
                    }

                    len = r->header_in->end - p;

                    if (len > NGX_MAX_ERROR_STR - 300) {
                        len = NGX_MAX_ERROR_STR - 300;
                    }

                    ngx_log_error(NGX_LOG_INFO, c->log, 0,
                                "client sent too long header line: \"%*s...\"",
                                len, r->header_name_start);

                    ngx_http_finalize_request(r,
                                            NGX_HTTP_REQUEST_HEADER_TOO_LARGE);
                    break;
                }
            }
            // 将会尝试读取更多的 header 数据
            n = ngx_http_read_request_header(r);

            if (n == NGX_AGAIN || n == NGX_ERROR) {
                break;
            }
        }

        /* the host header could change the server configuration context */
        cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
        // 重新解析 header 信息
        rc = ngx_http_parse_header_line(r, r->header_in,
                                        cscf->underscores_in_headers);

        if (rc == NGX_OK) {

            r->request_length += r->header_in->pos - r->header_name_start;

            if (r->invalid_header && cscf->ignore_invalid_headers) {

                /* there was error while a header line parsing */

                ngx_log_error(NGX_LOG_INFO, c->log, 0,
                              "client sent invalid header line: \"%*s\"",
                              r->header_end - r->header_name_start,
                              r->header_name_start);
                continue;
            }

            /* a header line has been parsed successfully */

            h = ngx_list_push(&r->headers_in.headers);
            if (h == NULL) {
                ngx_http_close_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                break;
            }

            h->hash = r->header_hash;

            h->key.len = r->header_name_end - r->header_name_start;
            h->key.data = r->header_name_start;
            h->key.data[h->key.len] = '\0';

            h->value.len = r->header_end - r->header_start;
            h->value.data = r->header_start;
            h->value.data[h->value.len] = '\0';

            h->lowcase_key = ngx_pnalloc(r->pool, h->key.len);
            if (h->lowcase_key == NULL) {
                ngx_http_close_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                break;
            }

            if (h->key.len == r->lowcase_index) {
                ngx_memcpy(h->lowcase_key, r->lowcase_header, h->key.len);

            } else {
                ngx_strlow(h->lowcase_key, h->key.data, h->key.len);
            }

            hh = ngx_hash_find(&cmcf->headers_in_hash, h->hash,
                               h->lowcase_key, h->key.len);
            // ngx_http_process_host, 处理 host 验证
            // ngx_http_process_connection, 处理 keepalive 
            if (hh && hh->handler(r, h, hh->offset) != NGX_OK) {
                break;
            }

            ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                           "http header: \"%V: %V\"",
                           &h->key, &h->value);

            continue;
        }
        // header 解析完成后, 处理body 数据了
        if (rc == NGX_HTTP_PARSE_HEADER_DONE) {

            /* a whole header has been parsed successfully */

            ngx_log_debug0(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                           "http header done");

            r->request_length += r->header_in->pos - r->header_name_start;

            r->http_state = NGX_HTTP_PROCESS_REQUEST_STATE;

            rc = ngx_http_process_request_header(r);

            if (rc != NGX_OK) {
                break;
            }

            ngx_http_process_request(r);

            break;
        }

        if (rc == NGX_AGAIN) {

            /* a header line parsing is still not complete */

            continue;
        }

        /* rc == NGX_HTTP_PARSE_INVALID_HEADER */

        ngx_log_error(NGX_LOG_INFO, c->log, 0,
                      "client sent invalid header line");

        ngx_http_finalize_request(r, NGX_HTTP_BAD_REQUEST);
        break;
    }

    ngx_http_run_posted_requests(c);
}

  以上是整个http的主要流程之一, 主要分为读取 header 处理header, 读取body处理body, 最后 ngx_http_run_posted_requests, 做后置处理. 其中重要的实现方式是, 依次读取每个字节, 进行http协议解析, 按行划分 header, 以及读取部分buffer就处理部分header等优化.

  接下来, 我们看看其对 body 部分的处理:

// http/ngx_http_request.c
// 处理 body 部分处理, 并处理响应对应请求
void
ngx_http_process_request(ngx_http_request_t *r)
{
    ngx_connection_t  *c;

    c = r->connection;

#if (NGX_HTTP_SSL)
    // https 处理...
#endif
    // 删除  timer
    if (c->read->timer_set) {
        ngx_del_timer(c->read);
    }

#if (NGX_STAT_STUB)
    (void) ngx_atomic_fetch_add(ngx_stat_reading, -1);
    r->stat_reading = 0;
    (void) ngx_atomic_fetch_add(ngx_stat_writing, 1);
    r->stat_writing = 1;
#endif
    // 设置读写 handler 为 ngx_http_request_handler, 以便在必要的时候使用
    c->read->handler = ngx_http_request_handler;
    c->write->handler = ngx_http_request_handler;
    r->read_event_handler = ngx_http_block_reading;
    // 由 ngx_http_handler 处理细节, 下节再看
    ngx_http_handler(r);
}

// http/ngx_http_request.c
// 读写处理器
static void
ngx_http_request_handler(ngx_event_t *ev)
{
    ngx_connection_t    *c;
    ngx_http_request_t  *r;

    c = ev->data;
    r = c->data;

    ngx_http_set_log_request(c->log, r);

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http run request: \"%V?%V\"", &r->uri, &r->args);

    if (c->close) {
        r->main->count++;
        ngx_http_terminate_request(r, 0);
        ngx_http_run_posted_requests(c);
        return;
    }

    if (ev->delayed && ev->timedout) {
        ev->delayed = 0;
        ev->timedout = 0;
    }

    if (ev->write) {
        r->write_event_handler(r);

    } else {
        r->read_event_handler(r);
    }

    ngx_http_run_posted_requests(c);
}

  大体就是如何使用 recv() 读取数据的过程, 看着流程多, 但实际上其时间复杂度基本为 O(1), 所以效率蛮高的.

 

3. http 请求的处理

  经过数据准备, 数据解析后, 就可以进行逻辑处理了. ngx 中支持许多的功能操作, 如配置内容跳转, 反向代理, 负载均衡 等等. 这些都统一归为一类操作.

void
ngx_http_handler(ngx_http_request_t *r)
{
    ngx_http_core_main_conf_t  *cmcf;

    r->connection->log->action = NULL;
    // 设置 keepalive 标识
    if (!r->internal) {
        switch (r->headers_in.connection_type) {
        case 0:
            r->keepalive = (r->http_version > NGX_HTTP_VERSION_10);
            break;

        case NGX_HTTP_CONNECTION_CLOSE:
            r->keepalive = 0;
            break;

        case NGX_HTTP_CONNECTION_KEEP_ALIVE:
            r->keepalive = 1;
            break;
        }

        r->lingering_close = (r->headers_in.content_length_n > 0
                              || r->headers_in.chunked);
        r->phase_handler = 0;

    } else {
        cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
        r->phase_handler = cmcf->phase_engine.server_rewrite_index;
    }

    r->valid_location = 1;
#if (NGX_HTTP_GZIP)
    r->gzip_tested = 0;
    r->gzip_ok = 0;
    r->gzip_vary = 0;
#endif
    // 设置写处理器为 ngx_http_core_run_phases, 即开始响应客户端流程
    r->write_event_handler = ngx_http_core_run_phases;
    ngx_http_core_run_phases(r);
}

// http/ngx_http_core_module.c
// 响应客户端操作, 多阶段式操作
void
ngx_http_core_run_phases(ngx_http_request_t *r)
{
    ngx_int_t                   rc;
    ngx_http_phase_handler_t   *ph;
    ngx_http_core_main_conf_t  *cmcf;

    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);

    ph = cmcf->phase_engine.handlers;
    // 依次调用各 checker, 直到有响应 OK 的checker为止
    while (ph[r->phase_handler].checker) {
        // 每次调用 checker 之后, 内部都会将 r->phase_handler++, 即迭代下一个
        // 此处的 checker 非常之多, 是在各模块启动时, 自动向 ngx_http_core_module.main_conf 中进行注册的
        /** 
         * 定义如下:
        typedef enum {
            NGX_HTTP_POST_READ_PHASE = 0,

            NGX_HTTP_SERVER_REWRITE_PHASE,

            NGX_HTTP_FIND_CONFIG_PHASE,
            NGX_HTTP_REWRITE_PHASE,
            NGX_HTTP_POST_REWRITE_PHASE,

            NGX_HTTP_PREACCESS_PHASE,

            NGX_HTTP_ACCESS_PHASE,
            NGX_HTTP_POST_ACCESS_PHASE,

            NGX_HTTP_PRECONTENT_PHASE,

            NGX_HTTP_CONTENT_PHASE,

            NGX_HTTP_LOG_PHASE
        } ngx_http_phases;

        // 注册方式
        cmcf = ngx_http_conf_get_module_main_conf(cf, ngx_http_core_module);
        h = ngx_array_push(&cmcf->phases[NGX_HTTP_ACCESS_PHASE].handlers);
        *h = ngx_http_access_handler;
        */
        // 将请求信息和 handler 本身传入调用(不是面向, 只能这么做了)
        rc = ph[r->phase_handler].checker(r, &ph[r->phase_handler]);
        // 只要有一个处理成功, 则后续不再调用
        if (rc == NGX_OK) {
            return;
        }
    }
}


// http/modules/ngx_http_rewrite_module.c
// 路径重写模块
ngx_int_t
ngx_http_core_rewrite_phase(ngx_http_request_t *r, ngx_http_phase_handler_t *ph)
{
    ngx_int_t  rc;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "rewrite phase: %ui", r->phase_handler);

    rc = ph->handler(r);

    if (rc == NGX_DECLINED) {
        r->phase_handler++;
        return NGX_AGAIN;
    }

    if (rc == NGX_DONE) {
        return NGX_OK;
    }

    /* NGX_OK, NGX_AGAIN, NGX_ERROR, NGX_HTTP_...  */

    ngx_http_finalize_request(r, rc);

    return NGX_OK;
}
static ngx_int_t
ngx_http_rewrite_handler(ngx_http_request_t *r)
{
    ngx_int_t                     index;
    ngx_http_script_code_pt       code;
    ngx_http_script_engine_t     *e;
    ngx_http_core_srv_conf_t     *cscf;
    ngx_http_core_main_conf_t    *cmcf;
    ngx_http_rewrite_loc_conf_t  *rlcf;

    cmcf = ngx_http_get_module_main_conf(r, ngx_http_core_module);
    cscf = ngx_http_get_module_srv_conf(r, ngx_http_core_module);
    index = cmcf->phase_engine.location_rewrite_index;

    if (r->phase_handler == index && r->loc_conf == cscf->ctx->loc_conf) {
        /* skipping location rewrite phase for server null location */
        return NGX_DECLINED;
    }

    rlcf = ngx_http_get_module_loc_conf(r, ngx_http_rewrite_module);

    if (rlcf->codes == NULL) {
        return NGX_DECLINED;
    }

    e = ngx_pcalloc(r->pool, sizeof(ngx_http_script_engine_t));
    if (e == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    e->sp = ngx_pcalloc(r->pool,
                        rlcf->stack_size * sizeof(ngx_http_variable_value_t));
    if (e->sp == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    e->ip = rlcf->codes->elts;
    e->request = r;
    e->quote = 1;
    e->log = rlcf->log;
    e->status = NGX_DECLINED;

    while (*(uintptr_t *) e->ip) {
        code = *(ngx_http_script_code_pt *) e->ip;
        code(e);
    }

    return e->status;
}

// http/modules/ngx_http_core_module.c
ngx_int_t
ngx_http_core_find_config_phase(ngx_http_request_t *r,
    ngx_http_phase_handler_t *ph)
{
    u_char                    *p;
    size_t                     len;
    ngx_int_t                  rc;
    ngx_http_core_loc_conf_t  *clcf;

    r->content_handler = NULL;
    r->uri_changed = 0;

    rc = ngx_http_core_find_location(r);

    if (rc == NGX_ERROR) {
        ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
        return NGX_OK;
    }

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    if (!r->internal && clcf->internal) {
        ngx_http_finalize_request(r, NGX_HTTP_NOT_FOUND);
        return NGX_OK;
    }

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "using configuration \"%s%V\"",
                   (clcf->noname ? "*" : (clcf->exact_match ? "=" : "")),
                   &clcf->name);

    ngx_http_update_location_config(r);

    ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "http cl:%O max:%O",
                   r->headers_in.content_length_n, clcf->client_max_body_size);

    if (r->headers_in.content_length_n != -1
        && !r->discard_body
        && clcf->client_max_body_size
        && clcf->client_max_body_size < r->headers_in.content_length_n)
    {
        ngx_log_error(NGX_LOG_ERR, r->connection->log, 0,
                      "client intended to send too large body: %O bytes",
                      r->headers_in.content_length_n);

        r->expect_tested = 1;
        (void) ngx_http_discard_request_body(r);
        ngx_http_finalize_request(r, NGX_HTTP_REQUEST_ENTITY_TOO_LARGE);
        return NGX_OK;
    }

    if (rc == NGX_DONE) {
        ngx_http_clear_location(r);

        r->headers_out.location = ngx_list_push(&r->headers_out.headers);
        if (r->headers_out.location == NULL) {
            ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
            return NGX_OK;
        }

        r->headers_out.location->hash = 1;
        ngx_str_set(&r->headers_out.location->key, "Location");

        if (r->args.len == 0) {
            r->headers_out.location->value = clcf->name;

        } else {
            len = clcf->name.len + 1 + r->args.len;
            p = ngx_pnalloc(r->pool, len);

            if (p == NULL) {
                ngx_http_clear_location(r);
                ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                return NGX_OK;
            }

            r->headers_out.location->value.len = len;
            r->headers_out.location->value.data = p;

            p = ngx_cpymem(p, clcf->name.data, clcf->name.len);
            *p++ = '?';
            ngx_memcpy(p, r->args.data, r->args.len);
        }

        ngx_http_finalize_request(r, NGX_HTTP_MOVED_PERMANENTLY);
        return NGX_OK;
    }

    r->phase_handler++;
    return NGX_AGAIN;
}

// http/ngx_http_core_module.c
ngx_int_t
ngx_http_core_generic_phase(ngx_http_request_t *r, ngx_http_phase_handler_t *ph)
{
    ngx_int_t  rc;

    /*
     * generic phase checker,
     * used by the post read and pre-access phases
     */

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                   "generic phase: %ui", r->phase_handler);

    rc = ph->handler(r);

    if (rc == NGX_OK) {
        r->phase_handler = ph->next;
        return NGX_AGAIN;
    }

    if (rc == NGX_DECLINED) {
        r->phase_handler++;
        return NGX_AGAIN;
    }

    if (rc == NGX_AGAIN || rc == NGX_DONE) {
        return NGX_OK;
    }

    /* rc == NGX_ERROR || rc == NGX_HTTP_...  */

    ngx_http_finalize_request(r, rc);

    return NGX_OK;
}

static ngx_int_t
ngx_http_index_handler(ngx_http_request_t *r)
{
    u_char                       *p, *name;
    size_t                        len, root, reserve, allocated;
    ngx_int_t                     rc;
    ngx_str_t                     path, uri;
    ngx_uint_t                    i, dir_tested;
    ngx_http_index_t             *index;
    ngx_open_file_info_t          of;
    ngx_http_script_code_pt       code;
    ngx_http_script_engine_t      e;
    ngx_http_core_loc_conf_t     *clcf;
    ngx_http_index_loc_conf_t    *ilcf;
    ngx_http_script_len_code_pt   lcode;

    if (r->uri.data[r->uri.len - 1] != '/') {
        return NGX_DECLINED;
    }

    if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD|NGX_HTTP_POST))) {
        return NGX_DECLINED;
    }

    ilcf = ngx_http_get_module_loc_conf(r, ngx_http_index_module);
    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    allocated = 0;
    root = 0;
    dir_tested = 0;
    name = NULL;
    /* suppress MSVC warning */
    path.data = NULL;

    index = ilcf->indices->elts;
    for (i = 0; i < ilcf->indices->nelts; i++) {

        if (index[i].lengths == NULL) {

            if (index[i].name.data[0] == '/') {
                return ngx_http_internal_redirect(r, &index[i].name, &r->args);
            }

            reserve = ilcf->max_index_len;
            len = index[i].name.len;

        } else {
            ngx_memzero(&e, sizeof(ngx_http_script_engine_t));

            e.ip = index[i].lengths->elts;
            e.request = r;
            e.flushed = 1;

            /* 1 is for terminating '\0' as in static names */
            len = 1;

            while (*(uintptr_t *) e.ip) {
                lcode = *(ngx_http_script_len_code_pt *) e.ip;
                len += lcode(&e);
            }

            /* 16 bytes are preallocation */

            reserve = len + 16;
        }

        if (reserve > allocated) {

            name = ngx_http_map_uri_to_path(r, &path, &root, reserve);
            if (name == NULL) {
                return NGX_HTTP_INTERNAL_SERVER_ERROR;
            }

            allocated = path.data + path.len - name;
        }

        if (index[i].values == NULL) {

            /* index[i].name.len includes the terminating '\0' */

            ngx_memcpy(name, index[i].name.data, index[i].name.len);

            path.len = (name + index[i].name.len - 1) - path.data;

        } else {
            e.ip = index[i].values->elts;
            e.pos = name;

            while (*(uintptr_t *) e.ip) {
                code = *(ngx_http_script_code_pt *) e.ip;
                code((ngx_http_script_engine_t *) &e);
            }

            if (*name == '/') {
                uri.len = len - 1;
                uri.data = name;
                return ngx_http_internal_redirect(r, &uri, &r->args);
            }

            path.len = e.pos - path.data;

            *e.pos = '\0';
        }

        ngx_log_debug1(NGX_LOG_DEBUG_HTTP, r->connection->log, 0,
                       "open index \"%V\"", &path);

        ngx_memzero(&of, sizeof(ngx_open_file_info_t));

        of.read_ahead = clcf->read_ahead;
        of.directio = clcf->directio;
        of.valid = clcf->open_file_cache_valid;
        of.min_uses = clcf->open_file_cache_min_uses;
        of.test_only = 1;
        of.errors = clcf->open_file_cache_errors;
        of.events = clcf->open_file_cache_events;

        if (ngx_http_set_disable_symlinks(r, clcf, &path, &of) != NGX_OK) {
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        if (ngx_open_cached_file(clcf->open_file_cache, &path, &of, r->pool)
            != NGX_OK)
        {
            if (of.err == 0) {
                return NGX_HTTP_INTERNAL_SERVER_ERROR;
            }

            ngx_log_debug2(NGX_LOG_DEBUG_HTTP, r->connection->log, of.err,
                           "%s \"%s\" failed", of.failed, path.data);

#if (NGX_HAVE_OPENAT)
            if (of.err == NGX_EMLINK
                || of.err == NGX_ELOOP)
            {
                return NGX_HTTP_FORBIDDEN;
            }
#endif

            if (of.err == NGX_ENOTDIR
                || of.err == NGX_ENAMETOOLONG
                || of.err == NGX_EACCES)
            {
                return ngx_http_index_error(r, clcf, path.data, of.err);
            }

            if (!dir_tested) {
                rc = ngx_http_index_test_dir(r, clcf, path.data, name - 1);

                if (rc != NGX_OK) {
                    return rc;
                }

                dir_tested = 1;
            }

            if (of.err == NGX_ENOENT) {
                continue;
            }

            ngx_log_error(NGX_LOG_CRIT, r->connection->log, of.err,
                          "%s \"%s\" failed", of.failed, path.data);

            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        uri.len = r->uri.len + len - 1;

        if (!clcf->alias) {
            uri.data = path.data + root;

        } else {
            uri.data = ngx_pnalloc(r->pool, uri.len);
            if (uri.data == NULL) {
                return NGX_HTTP_INTERNAL_SERVER_ERROR;
            }

            p = ngx_copy(uri.data, r->uri.data, r->uri.len);
            ngx_memcpy(p, name, len - 1);
        }

        return ngx_http_internal_redirect(r, &uri, &r->args);
    }

    return NGX_DECLINED;
}


static ngx_int_t
ngx_http_static_handler(ngx_http_request_t *r)
{
    u_char                    *last, *location;
    size_t                     root, len;
    ngx_str_t                  path;
    ngx_int_t                  rc;
    ngx_uint_t                 level;
    ngx_log_t                 *log;
    ngx_buf_t                 *b;
    ngx_chain_t                out;
    ngx_open_file_info_t       of;
    ngx_http_core_loc_conf_t  *clcf;

    if (!(r->method & (NGX_HTTP_GET|NGX_HTTP_HEAD|NGX_HTTP_POST))) {
        return NGX_HTTP_NOT_ALLOWED;
    }

    if (r->uri.data[r->uri.len - 1] == '/') {
        return NGX_DECLINED;
    }

    log = r->connection->log;

    /*
     * ngx_http_map_uri_to_path() allocates memory for terminating '\0'
     * so we do not need to reserve memory for '/' for possible redirect
     */

    last = ngx_http_map_uri_to_path(r, &path, &root, 0);
    if (last == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    path.len = last - path.data;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, log, 0,
                   "http filename: \"%s\"", path.data);

    clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

    ngx_memzero(&of, sizeof(ngx_open_file_info_t));

    of.read_ahead = clcf->read_ahead;
    of.directio = clcf->directio;
    of.valid = clcf->open_file_cache_valid;
    of.min_uses = clcf->open_file_cache_min_uses;
    of.errors = clcf->open_file_cache_errors;
    of.events = clcf->open_file_cache_events;

    if (ngx_http_set_disable_symlinks(r, clcf, &path, &of) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    if (ngx_open_cached_file(clcf->open_file_cache, &path, &of, r->pool)
        != NGX_OK)
    {
        switch (of.err) {

        case 0:
            return NGX_HTTP_INTERNAL_SERVER_ERROR;

        case NGX_ENOENT:
        case NGX_ENOTDIR:
        case NGX_ENAMETOOLONG:

            level = NGX_LOG_ERR;
            rc = NGX_HTTP_NOT_FOUND;
            break;

        case NGX_EACCES:
#if (NGX_HAVE_OPENAT)
        case NGX_EMLINK:
        case NGX_ELOOP:
#endif

            level = NGX_LOG_ERR;
            rc = NGX_HTTP_FORBIDDEN;
            break;

        default:

            level = NGX_LOG_CRIT;
            rc = NGX_HTTP_INTERNAL_SERVER_ERROR;
            break;
        }

        if (rc != NGX_HTTP_NOT_FOUND || clcf->log_not_found) {
            ngx_log_error(level, log, of.err,
                          "%s \"%s\" failed", of.failed, path.data);
        }

        return rc;
    }

    r->root_tested = !r->error_page;

    ngx_log_debug1(NGX_LOG_DEBUG_HTTP, log, 0, "http static fd: %d", of.fd);

    if (of.is_dir) {

        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, log, 0, "http dir");

        ngx_http_clear_location(r);

        r->headers_out.location = ngx_list_push(&r->headers_out.headers);
        if (r->headers_out.location == NULL) {
            return NGX_HTTP_INTERNAL_SERVER_ERROR;
        }

        len = r->uri.len + 1;

        if (!clcf->alias && r->args.len == 0) {
            location = path.data + root;

            *last = '/';

        } else {
            if (r->args.len) {
                len += r->args.len + 1;
            }

            location = ngx_pnalloc(r->pool, len);
            if (location == NULL) {
                ngx_http_clear_location(r);
                return NGX_HTTP_INTERNAL_SERVER_ERROR;
            }

            last = ngx_copy(location, r->uri.data, r->uri.len);

            *last = '/';

            if (r->args.len) {
                *++last = '?';
                ngx_memcpy(++last, r->args.data, r->args.len);
            }
        }

        r->headers_out.location->hash = 1;
        ngx_str_set(&r->headers_out.location->key, "Location");
        r->headers_out.location->value.len = len;
        r->headers_out.location->value.data = location;

        return NGX_HTTP_MOVED_PERMANENTLY;
    }

#if !(NGX_WIN32) /* the not regular files are probably Unix specific */

    if (!of.is_file) {
        ngx_log_error(NGX_LOG_CRIT, log, 0,
                      "\"%s\" is not a regular file", path.data);

        return NGX_HTTP_NOT_FOUND;
    }

#endif

    if (r->method == NGX_HTTP_POST) {
        return NGX_HTTP_NOT_ALLOWED;
    }

    rc = ngx_http_discard_request_body(r);

    if (rc != NGX_OK) {
        return rc;
    }

    log->action = "sending response to client";

    r->headers_out.status = NGX_HTTP_OK;
    r->headers_out.content_length_n = of.size;
    r->headers_out.last_modified_time = of.mtime;

    if (ngx_http_set_etag(r) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    if (ngx_http_set_content_type(r) != NGX_OK) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    if (r != r->main && of.size == 0) {
        return ngx_http_send_header(r);
    }

    r->allow_ranges = 1;

    /* we need to allocate all before the header would be sent */

    b = ngx_calloc_buf(r->pool);
    if (b == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    b->file = ngx_pcalloc(r->pool, sizeof(ngx_file_t));
    if (b->file == NULL) {
        return NGX_HTTP_INTERNAL_SERVER_ERROR;
    }

    rc = ngx_http_send_header(r);

    if (rc == NGX_ERROR || rc > NGX_OK || r->header_only) {
        return rc;
    }

    b->file_pos = 0;
    b->file_last = of.size;

    b->in_file = b->file_last ? 1: 0;
    b->last_buf = (r == r->main) ? 1: 0;
    b->last_in_chain = 1;

    b->file->fd = of.fd;
    b->file->name = path;
    b->file->log = log;
    b->file->directio = of.is_directio;

    out.buf = b;
    out.next = NULL;

    return ngx_http_output_filter(r, &out);
}

// http/ngx_http_request.c
void
ngx_http_finalize_request(ngx_http_request_t *r, ngx_int_t rc)
{
    ngx_connection_t          *c;
    ngx_http_request_t        *pr;
    ngx_http_core_loc_conf_t  *clcf;

    c = r->connection;

    ngx_log_debug5(NGX_LOG_DEBUG_HTTP, c->log, 0,
                   "http finalize request: %i, \"%V?%V\" a:%d, c:%d",
                   rc, &r->uri, &r->args, r == c->data, r->main->count);

    if (rc == NGX_DONE) {
        ngx_http_finalize_connection(r);
        return;
    }

    if (rc == NGX_OK && r->filter_finalize) {
        c->error = 1;
    }

    if (rc == NGX_DECLINED) {
        r->content_handler = NULL;
        r->write_event_handler = ngx_http_core_run_phases;
        ngx_http_core_run_phases(r);
        return;
    }

    if (r != r->main && r->post_subrequest) {
        rc = r->post_subrequest->handler(r, r->post_subrequest->data, rc);
    }

    if (rc == NGX_ERROR
        || rc == NGX_HTTP_REQUEST_TIME_OUT
        || rc == NGX_HTTP_CLIENT_CLOSED_REQUEST
        || c->error)
    {
        if (ngx_http_post_action(r) == NGX_OK) {
            return;
        }

        ngx_http_terminate_request(r, rc);
        return;
    }

    if (rc >= NGX_HTTP_SPECIAL_RESPONSE
        || rc == NGX_HTTP_CREATED
        || rc == NGX_HTTP_NO_CONTENT)
    {
        if (rc == NGX_HTTP_CLOSE) {
            c->timedout = 1;
            ngx_http_terminate_request(r, rc);
            return;
        }

        if (r == r->main) {
            if (c->read->timer_set) {
                ngx_del_timer(c->read);
            }

            if (c->write->timer_set) {
                ngx_del_timer(c->write);
            }
        }

        c->read->handler = ngx_http_request_handler;
        c->write->handler = ngx_http_request_handler;

        ngx_http_finalize_request(r, ngx_http_special_response_handler(r, rc));
        return;
    }

    if (r != r->main) {

        if (r->buffered || r->postponed) {

            if (ngx_http_set_write_handler(r) != NGX_OK) {
                ngx_http_terminate_request(r, 0);
            }

            return;
        }

        pr = r->parent;

        if (r == c->data || r->background) {

            if (!r->logged) {

                clcf = ngx_http_get_module_loc_conf(r, ngx_http_core_module);

                if (clcf->log_subrequest) {
                    ngx_http_log_request(r);
                }

                r->logged = 1;

            } else {
                ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                              "subrequest: \"%V?%V\" logged again",
                              &r->uri, &r->args);
            }

            r->done = 1;

            if (r->background) {
                ngx_http_finalize_connection(r);
                return;
            }

            r->main->count--;

            if (pr->postponed && pr->postponed->request == r) {
                pr->postponed = pr->postponed->next;
            }

            c->data = pr;

        } else {

            ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                           "http finalize non-active request: \"%V?%V\"",
                           &r->uri, &r->args);

            r->write_event_handler = ngx_http_request_finalizer;

            if (r->waited) {
                r->done = 1;
            }
        }

        if (ngx_http_post_request(pr, NULL) != NGX_OK) {
            r->main->count++;
            ngx_http_terminate_request(r, 0);
            return;
        }

        ngx_log_debug2(NGX_LOG_DEBUG_HTTP, c->log, 0,
                       "http wake parent request: \"%V?%V\"",
                       &pr->uri, &pr->args);

        return;
    }

    if (r->buffered || c->buffered || r->postponed) {

        if (ngx_http_set_write_handler(r) != NGX_OK) {
            ngx_http_terminate_request(r, 0);
        }

        return;
    }

    if (r != c->data) {
        ngx_log_error(NGX_LOG_ALERT, c->log, 0,
                      "http finalize non-active request: \"%V?%V\"",
                      &r->uri, &r->args);
        return;
    }

    r->done = 1;

    r->read_event_handler = ngx_http_block_reading;
    r->write_event_handler = ngx_http_request_empty_handler;

    if (!r->post_action) {
        r->request_complete = 1;
    }

    if (ngx_http_post_action(r) == NGX_OK) {
        return;
    }

    if (c->read->timer_set) {
        ngx_del_timer(c->read);
    }

    if (c->write->timer_set) {
        c->write->delayed = 0;
        ngx_del_timer(c->write);
    }

    if (c->read->eof) {
        ngx_http_close_request(r, 0);
        return;
    }

    ngx_http_finalize_connection(r);
}

      可以看出,nginx处理http流程框架非常简单,即一直遍历执行所有checker,但本身checker数量又比较多,所以给我们的处理带来了复杂度。此处相当于是责任链模式的应用,而且这链是可以被任意注册的,所以也为我们扩展性打开了方便之门。从部分上按一定序执行checker,只要有一个处理完成,即带调用后续checker。

      这些checker大体上被分为了几类,body数据读取类,config配置文件读取类,rewrite路径重写类,access权限验证类,content内容处理类,log日志记录类。从总体上是有序的,但对于某类处理,则是任意的。

  本文讲解了nginx作为正向代理(http服务器)的处理过程,当然我们可以简单认为是一个文件路径查找的过程。无非就是解析请求头请求体信息,然后查找所有可能的地方,验证可能的权限,然后就输出内容到客户端了。其实和其他的http服务器没啥差别,但nginx的优势在于性能,在于配置的简便性。性能上基于非阻塞io,配置上则已形成自有的一套简洁语法。

posted @ 2020-09-27 22:27  等你归去来  阅读(52)  评论(0编辑  收藏