前面我們介紹了Mongoose所有的幾個主要的數據結構mg_context、mg_connection、mg_request_info,還有Mongoose的生命主線。有了這些基礎就可以來看看Mongoose的核心處理工作是怎樣的。如果你還沒有閱讀前面的文章,你可以通過下面的隧道直通:
- Mongoose源碼剖析:外篇之web服務器
- Mongoose源碼剖析:Introduction and Installation
- Mongoose源碼剖析:數據結構篇
- Mongoose源碼剖析:mongoose的工作模型
本文從下面幾個方面去介紹Mongoose的核心處理模塊,連接建立之後的:
- 請求解析
- 請求驗證
- 請求滿足
1、連接的建立
Mongoose的主線程master_thread在接受一個新的client連接請求時,會將client的socket地址放入一個queue(調用put_socket()方法);而當worker_thread線程處理client的請求時,是通過get_socket()方法從queue取出client的socket地址,然後與它建立連接。
建立連接就用到了數據結構mg_connection,該結構保存了client的連接信息。該結構體中有兩個非常重要的成員:mg_request_info用於保存client的請求信息、mg_context用於保存該client請求的mongoose上下文。建立連接的代碼片段如下:
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_開頭的函數都是加載自SSL的庫,加載庫調用瞭如下接口:static bool_t set_ssl_option(struct mg_context *ctx, const char *pem),有興趣的話你可以追蹤下去。
2、請求信息獲取
建立連接之後,在process_new_connection中會去讀取client的請求信息,然後纔去解析請求。讀取client端的請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()方法的代碼如下:
/* * 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); }
這樣client發送的HTTP請求消息就被worker_thread讀取到了,並存儲在buf中, 接下來的工作就是解析讀取到的請求信息,明白client到底想幹嘛,說白了就從buf中提取信息並存儲到結構體mg_request_info中去。
3、請求解析
請求解析的工作都封裝在parse_http_request()函數匯中,它的代碼如下:
/* * 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); }
它的主要工作就是從buf中提取出信息放到ri(一個mg_request_info結構)中去,因爲buf是一個無結構的字符串數組。要將它存儲到ri中去,需要找到對應的子串。
這裏主要用到了skip()、parse_http_headers()方法,其中skip()很關鍵,代碼如下:
/* * 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); }
我們來分析一下skip的作用及實現。如要從buf中解析出client請求的methods是哪個(PUT、GET、POST等等)?只需要這樣做就可以了:
ri->request_method = skip(&buf, " ");
爲了分析,到底是如何實現這個的,我在porcess_new_connection()中加入下面一行輸出buf信息的代碼:
看當我們想mongoose發送的請求信息,這時我們在瀏覽其中輸入http://ip:8080,終端會輸出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,但在我們分析skip(&buf, " ")是如何提取出GET的之前,還要知道strcspn、strspn的作用,下面是它們的原型:
#include <string.h> size_t strspn(const char *s, const char *accept); size_t strcspn(const char *s, const char *reject);
下面解釋它們的作用:
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.
現在已經萬事俱備了,skip(&buf, " ")的執行情況如下:
其餘的解析工作也是類似地進行的,我就不一一闡述了。
4、請求驗證
請求驗證分佈在從連接請求開始到請求得到迴應的整個過程中。在請求解析之前,比如驗證socket的合法性等。在請求解析之後,從buf中解析出HTTP請求消息的各個字段之後,就做一些簡單的驗證工作,比如說HTTP版本的驗證。如果在解析buf時出錯,說明請求的格式不對。
而且在滿足client請求的時候也要進行一些驗證,諸如是否有瀏覽目錄的權限、請求的文件是否存在等等,我就不在詳述了。
5、請求滿足
在parse_http_request()之後,調用analyze_request()去滿足client的請求。這是Mongoose的核心內容,也是不同web服務器軟件相區別的地方。analyze_request()封裝了一些操作,即調用了一些接口去滿足client的請求,代碼如下:
/* * 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); } }