Mongoose源码剖析：核心处理模块

引言

前面我们介绍了Mongoose所有的几个主要的数据结构mg_context、mg_connection、mg_request_info，还有Mongoose的生命主线。有了这些基础就可以来看看Mongoose的核心处理工作是怎样的。

本文从下面几个方面去介绍Mongoose的核心处理模块，连接建立之后的：

• 请求解析
• 请求验证
• 请求满足

1、连接的建立

Mongoose的主线程master_thread在接受一个新的client连接请求时，会将client的socket地址放入一个queue（调用put_socket()方法）；而当worker_thread线程处理client的请求时，是通过get_socket()方法从queue取出client的socket地址，然后与它建立连接。

建立连接就用到了数据结构mg_connection，该结构保存了client的连接信息。该结构体中有两个非常重要的成员：mg_request_info用于保存client的请求信息、mg_context用于保存该client请求的mongoose上下文。建立连接的代码片段如下：

while (get_socket(ctx, &conn.client) == TRUE) {
        conn.birth_time = time(NULL);
        conn.ctx = ctx;

        if (conn.client.is_ssl &&
            (conn.ssl = SSL_new(conn.ctx->ssl_ctx)) == NULL) {
            cry(&conn, "%s: SSL_new: %d", __func__, ERRNO);
        } else if (conn.client.is_ssl &&
            SSL_set_fd(conn.ssl, conn.client.sock) != 1) {
            cry(&conn, "%s: SSL_set_fd: %d", __func__, ERRNO);
        } else if (conn.client.is_ssl && SSL_accept(conn.ssl) != 1) {
            cry(&conn, "%s: SSL handshake error", __func__);
        } else {
            process_new_connection(&conn);
        }

        close_connection(&conn);
    }

其中以SSL_开头的函数都是加载自SSL的库，加载库调用了如下接口：static bool_t set_ssl_option(struct mg_context *ctx, const char *pem)，有兴趣的话你可以追踪下去。

2、请求信息获取

建立连接之后，在process_new_connection中会去读取client的请求信息，然后才去解析请求。读取client端的请求的信息用到了下面的方法：

/*
 * Keep reading the input (either opened file descriptor fd, or socket sock,
 * or SSL descriptor ssl) into buffer buf, until \r\n\r\n appears in the
 * buffer (which marks the end of HTTP request). Buffer buf may already
 * have some data. The length of the data is stored in nread.
 * Upon every read operation, increase nread by the number of bytes read.
 */
static int
read_request(FILE *fp, SOCKET sock, SSL *ssl, char *buf, int bufsiz, int *nread)
{
    int    n, request_len;

    request_len = 0;
    while (*nread < bufsiz && request_len == 0) {
        n = pull(fp, sock, ssl, buf + *nread, bufsiz - *nread);
        if (n <= 0) {
            break;
        } else {
            *nread += n;
            request_len = get_request_len(buf, (size_t) *nread);
        }
    }

    return (request_len);
}

其中pull()方法的代码如下：

/*
 * Read from IO channel - opened file descriptor, socket, or SSL descriptor.
 * Return number of bytes read.
 */
static int
pull(FILE *fp, SOCKET sock, SSL *ssl, char *buf, int len)
{
    int    nread;

    if (ssl != NULL) {
        nread = SSL_read(ssl, buf, len);
    } else if (fp != NULL) {
        nread = fread(buf, 1, (size_t) len, fp);
        if (ferror(fp))
            nread = -1;
    } else {
        nread = recv(sock, buf, (size_t) len, 0);
    }

    return (nread);
}

这样client发送的HTTP请求消息就被worker_thread读取到了，并存储在buf中， 接下来的工作就是解析读取到的请求信息，明白client到底想干嘛，说白了就从buf中提取信息并存储到结构体mg_request_info中去。

3、请求解析

请求解析的工作都封装在parse_http_request()函数汇中，它的代码如下：

/*
 * Parse HTTP request, fill in mg_request_info structure.
 */
static bool_t
parse_http_request(char *buf, struct mg_request_info *ri, const struct usa *usa)
{
    char    *http_version;
    int    n, success_code = FALSE;

    ri->request_method = skip(&buf, " ");
    ri->uri = skip(&buf, " ");
    http_version = skip(&buf, "\r\n");

    if (is_known_http_method(ri->request_method) &&
        ri->uri[0] == '/' &&
        sscanf(http_version, "HTTP/%d.%d%n",
        &ri->http_version_major, &ri->http_version_minor, &n) == 2 &&
        http_version[n] == '\0') {
        parse_http_headers(&buf, ri);
        ri->remote_port = ntohs(usa->u.sin.sin_port);
        (void) memcpy(&ri->remote_ip, &usa->u.sin.sin_addr.s_addr, 4);
        ri->remote_ip = ntohl(ri->remote_ip);
        success_code = TRUE;
    }

    return (success_code);
}

它的主要工作就是从buf中提取出信息放到ri（一个mg_request_info结构）中去，因为buf是一个无结构的字符串数组。要将它存储到ri中去，需要找到对应的子串。

这里主要用到了skip()、parse_http_headers()方法，其中skip()很关键，代码如下：

/*
 * Skip the characters until one of the delimiters characters found.
 * 0-terminate resulting word. Skip the rest of the delimiters if any.
 * Advance pointer to buffer to the next word. Return found 0-terminated word.
 */
static char *
skip(char **buf, const char *delimiters)
{
    char    *p, *begin_word, *end_word, *end_delimiters;

    begin_word = *buf;
    end_word = begin_word + strcspn(begin_word, delimiters);
    end_delimiters = end_word + strspn(end_word, delimiters);

    for (p = end_word; p < end_delimiters; p++)
        *p = '\0';

    *buf = end_delimiters;

    return (begin_word);
}

我们来分析一下skip的作用及实现。如要从buf中解析出client请求的methods是哪个（PUT、GET、POST等等）？只需要这样做就可以了： 

ri->request_method = skip(&buf, " "); 

为了分析，到底是如何实现这个的，我在porcess_new_connection()中加入下面一行输出buf信息的代码：

/在process_new_connection()中
/* 0-terminate the request: parse_request uses sscanf */
 buf[request_len - 1] = '\0';
//******************************************************************
//打印buf内容
printf("\n******process_new_connection()******\n");
printf("add by fanguotao,just for debug!!  receive request_info is \n%s",buf);
//******************************************************************

看当我们想mongoose发送的请求信息，这时我们在浏览其中输入，终端会输出buf的信息，如下：

      

看到第一行就是GET /favicon.ico HTTP/1.1。知道了buf中的字符信息，但在我们分析skip(&buf, " ")是如何提取出GET的之前，还要知道strcspn、strspn的作用，下面是它们的原型：

#include <string.h>
       size_t strspn(const char *s, const char *accept);
       size_t strcspn(const char *s, const char *reject);

下面解释它们的作用：

DESCRIPTION
       The strspn() function calculates the length of the initial segment of s
which consists entirely of characters in accept.

       The strcspn() function calculates the length of the initial segment  of s which consists entirely of characters not in reject.

RETURN VALUE
       The  strspn()  function returns the number of characters in the initial segment of s which consist only of characters from accept.

       The strcspn() function returns the number of characters in the  initial segment of s which are not in the string reject.

现在已经万事俱备了，skip(&buf, " ")的执行情况如下：

                 

4、请求验证

请求验证分布在从连接请求开始到请求得到回应的整个过程中。在请求解析之前，比如验证socket的合法性等。在请求解析之后，从buf中解析出HTTP请求消息的各个字段之后，就做一些简单的验证工作，比如说HTTP版本的验证。如果在解析buf时出错，说明请求的格式不对。

而且在满足client请求的时候也要进行一些验证，诸如是否有浏览目录的权限、请求的文件是否存在等等，我就不在详述了

5、请求满足

在parse_http_request()之后，调用analyze_request()去满足client的请求。这是Mongoose的核心内容，也是不同web服务器软件相区别的地方。analyze_request()封装了一些操作，即调用了一些接口去满足client的请求，代码如下：。

/*
 * This is the heart of the Mongoose's logic.
 * This function is called when the request is read, parsed and validated,
 * and Mongoose must decide what action to take: serve a file, or
 * a directory, or call embedded function, etcetera.
 */
static void
analyze_request(struct mg_connection *conn)
{
    struct mg_request_info *ri = &conn->request_info;
    char            path[FILENAME_MAX], *uri = ri->uri;
    struct mgstat        st;
    const struct callback    *cb;

    if ((conn->request_info.query_string = strchr(uri, '?')) != NULL)
        * conn->request_info.query_string++ = '\0';

    (void) url_decode(uri, (int) strlen(uri), uri, strlen(uri) + 1, FALSE);
    remove_double_dots_and_double_slashes(uri);
    convert_uri_to_file_name(conn, uri, path, sizeof(path));

    if (!check_authorization(conn, path)) {
        send_authorization_request(conn);
    } else if (check_embedded_authorization(conn) == FALSE) {
        /*
         * Embedded code failed authorization. Do nothing here, since
         * an embedded code must handle this itself by either
         * showing proper error message, or redirecting to some
         * sort of login page, or something else.
         */
    } else if ((cb = find_callback(conn->ctx, FALSE, uri, -1)) != NULL) {
        if ((strcmp(ri->request_method, "POST") != 0 &&
            strcmp(ri->request_method, "PUT") != 0) ||
            handle_request_body(conn, NULL))
            cb->func(conn, &conn->request_info, cb->user_data);
    } else if (strstr(path, PASSWORDS_FILE_NAME)) {
        /* Do not allow to view passwords files */
        send_error(conn, 403, "Forbidden", "Access Forbidden");
    } else if ((!strcmp(ri->request_method, "PUT") ||
        !strcmp(ri->request_method, "DELETE")) &&
        (conn->ctx->options[OPT_AUTH_PUT] == NULL ||
         !is_authorized_for_put(conn))) {
        send_authorization_request(conn);
    } else if (!strcmp(ri->request_method, "PUT")) {
        put_file(conn, path);
    } else if (!strcmp(ri->request_method, "DELETE")) {
        if (mg_remove(path) == 0)
            send_error(conn, 200, "OK", "");
        else
            send_error(conn, 500, http_500_error,
                "remove(%s): %s", path, strerror(ERRNO));
    } else if (mg_stat(path, &st) != 0) {
        send_error(conn, 404, "Not Found", "%s", "File not found");
    } else if (st.is_directory && uri[strlen(uri) - 1] != '/') {
        (void) mg_printf(conn,
            "HTTP/1.1 301 Moved Permanently\r\n"
            "Location: %s/\r\n\r\n", uri);
    } else if (st.is_directory &&
        substitute_index_file(conn, path, sizeof(path), &st) == FALSE) {
        if (is_true(conn->ctx->options[OPT_DIR_LIST])) {
            send_directory(conn, path);
        } else {
            send_error(conn, 403, "Directory Listing Denied",
                "Directory listing denied");
        }
#if !defined(NO_CGI)
    } else if (match_extension(path,
        conn->ctx->options[OPT_CGI_EXTENSIONS])) {
        if (strcmp(ri->request_method, "POST") &&
            strcmp(ri->request_method, "GET")) {
            send_error(conn, 501, "Not Implemented",
                "Method %s is not implemented", ri->request_method);
        } else {
            send_cgi(conn, path);
        }
#endif /* NO_CGI */
#if !defined(NO_SSI)
    } else if (match_extension(path,
        conn->ctx->options[OPT_SSI_EXTENSIONS])) {
        send_ssi(conn, path);
#endif /* NO_SSI */
    } else if (is_not_modified(conn, &st)) {
        send_error(conn, 304, "Not Modified", "");
    } else {
        send_file(conn, path, &st);
    }
}

  《通过反复的看，对mongoose—web服务器的工作原理有了较深的了解，其工作模型以及实现方法方面，非常值得学习继续努力哈，梦醒潇湘love》

本文来自：吴秦