Tinyhttpd源码解析

简介

Tinyhttpd是一轻量级的web服务器，它由美国学生J. David Blackstone于1999年在学习网络课程时编写。源码不到500行，非常适合学习Web编程和Linux/Unix编程接口。

其源码见Tinyhttpd

分析

Tinyhttpd执行流程如下图：

主线程完成socket的创建、绑定、端口监听、创建子线程处理每一个请求。代码如下：

int main(void){int server_sock = -1;u_short port = 8000;int client_sock = -1;struct sockaddr_in client_name;int client_name_len = sizeof(client_name);pthread_t newthread;/* 在指定端口上建立http服务 */server_sock = startup(&port);printf("httpd-socket:%d\n", server_sock);printf("httpd running on port %d\n", port);int count = 0;while (1) {/* accpet成功后，可获得客户端socket和sockaddr */client_sock = accept(server_sock,   (struct sockaddr *)&client_name,   &client_name_len);if (client_sock == -1)error_die("accept");/* accept_request(client_sock); */if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)perror("pthread_create");//printf("\b%d", ++count); fflush(stdout); //统计连接请求数}close(server_sock);return(0);}

其中startup()函数完成socket的bind/listen。代码实现如下：

/**********************************************************************//* This function starts the process of listening for web connections * on a specified port.  If the port is 0, then dynamically allocate a * port and modify the original port variable to reflect the actual * port. * Parameters: pointer to variable containing the port to connect on * Returns: the socket *//**********************************************************************/int startup(u_short *port){int httpd = 0;struct sockaddr_in name;/* 建立socket */httpd = socket(PF_INET, SOCK_STREAM, 0);if (httpd == -1)error_die("socket");memset(&name, 0, sizeof(name));name.sin_family = AF_INET;name.sin_port = htons(*port);name.sin_addr.s_addr = htonl(INADDR_ANY);/* 绑定socket */if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)error_die("bind");if (*port == 0) {  /* if dynamically allocating a port */int namelen = sizeof(name);if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)error_die("getsockname");*port = ntohs(name.sin_port);}/* 监听socket */if (listen(httpd, 5) < 0)error_die("listen");return(httpd);}

子线程accep_request()处理连接请求，请求处理完成后关闭连接。当然这种多线程方式，不可能做到高并发。每来一个请求都会创建一个子线程来处理，处理完成后结束子线程，这必然会导致服务器有不少性能开销，一般用线程池技术。当然Web服务也可以使用多进程如nginx。多线程共享父进程的数据空间，可能导致问题蔓延。多进程有很好的隔离性。accep_request()代码如下：

/**********************************************************************//* A request has caused a call to accept() on the server port to * return.  Process the request appropriately. * Parameters: the socket connected to the client *//**********************************************************************/void accept_request(int client){char buf[1024];int numchars;char method[255]; //请求方法char url[255]; //URLchar path[512];size_t i, j;struct stat st;int cgi = 0; /* becomes true if server decides this is a CGI program */char *query_string = NULL;/* 读取请求行 */numchars = get_line(client, buf, sizeof(buf));printf("Request-line:%s\n", buf); //debugi = 0; j = 0;/* 读取请求行中的请求方法至method */while (!ISspace(buf[j]) && (i < sizeof(method) - 1)) {method[i] = buf[j];i++; j++;}method[i] = '\0';printf("Method:%s ", method);/* 仅支持GET和POST请求方法 */if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) {unimplemented(client); //通知客户客，该请求方法未实现return;}/* POST时开启CGI */if (strcasecmp(method, "POST") == 0)cgi = 1;/* 读取请求行中URL */i = 0;while (ISspace(buf[j]) && (j < sizeof(buf)))j++;while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf))) {url[i] = buf[j];i++; j++;}url[i] = '\0';printf("URL:%s \n", url);/* 处理GET方法 */if (strcasecmp(method, "GET") == 0) { query_string = url;while ((*query_string != '?') && (*query_string != '\0'))query_string++;/* GET方法的特点，? 后面为参数 */if (*query_string == '?') {/* 开启CGI */cgi = 1;*query_string = '\0';query_string++;}}/* 格式化URL到path数组, html在htdocs中，从客户端发过来的URL至少是/ */sprintf(path, "htdocs%s", url);if (path[strlen(path) - 1] == '/')/* 默认情况为index.html */strcat(path, "index.html");/* 根据路径找到对应的文件 */if (stat(path, &st) == -1) {while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */numchars = get_line(client, buf, sizeof(buf)); //从客户端中把请求读完not_found(client);}else {if ((st.st_mode & S_IFMT) == S_IFDIR) //文件是目录strcat(path, "/index.html");/* 判断文件是否具有可执行权限 */if ((st.st_mode & S_IXUSR) || (st.st_mode & S_IXGRP) || (st.st_mode & S_IXOTH))cgi = 1;if (!cgi)serve_file(client, path);elseexecute_cgi(client, path, method, query_string);}/* 关闭连接，假定不是keepalive */close(client);}

浏览器是按照http协议请求的格式给服务器发送请求的，这个函数完成了http协议请求解析。目前只支持GET和POST请求。其中get_line()函数并且不管原来是以\n还是\r\n结束，均转化为以\n再加\0字符结束。实现代码如下：

/**********************************************************************//* Get a line from a socket, whether the line ends in a newline, * carriage return, or a CRLF combination.  Terminates the string read * with a null character.  If no newline indicator is found before the * end of the buffer, the string is terminated with a null.  If any of * the above three line terminators is read, the last character of the * string will be a linefeed and the string will be terminated with a * null character. * Parameters: the socket descriptor *             the buffer to save the data in *             the size of the buffer * Returns: the number of bytes stored (excluding null) *//**********************************************************************/int get_line(int sock, char *buf, int size){int i = 0;char c = '\0';int n;/*把终止条件统一为\n换行符，标准化buf数组*/while ((i < size - 1) && (c != '\n')) {/* 每次只接收一个字符 */n = recv(sock, &c, 1, 0);/* DEBUG printf("%02X\n", c); */if (n > 0) {/*收到\r则继续接收下个字节，因为换行符可能是\r\n */if (c == '\r') {/*MSG_PEEK使下一次读取的内容和本次读取的内容相同，可认为接收窗口不滑动*/n = recv(sock, &c, 1, MSG_PEEK); //提前偷窥下次内容/* DEBUG printf("%02X\n", c); */if ((n > 0) && (c == '\n'))recv(sock, &c, 1, 0);elsec = '\n';}buf[i] = c;i++;}elsec = '\n';}buf[i] = '\0';return(i);}

get_line完后，就是开始解析第一行，判断是GET方法还是POST方法，目前只支持这两种。如果是POST，还是把cgi置1，表明要运行CGI程序；如果是GET方法且附带以?开头的参数时，也认为是执行CGI程序。

获取URL得到文件在服务上的访问路径，获取访问文件的属性，并判断文件是否具有可执行权限。如果有可执行权限，则认为是要执行CGI程序。否则访问静态文件，访问方法为serve_file()，其实现如下：

 /**********************************************************************//* Send a regular file to the client.  Use headers, and report * errors to client if they occur. * Parameters: a pointer to a file structure produced from the socket *              file descriptor *             the name of the file to serve *//**********************************************************************/void serve_file(int client, const char *filename){FILE *resource = NULL;int numchars = 1;char buf[1024];/* 读取并丢弃headers */buf[0] = 'A'; buf[1] = '\0';while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */numchars = get_line(client, buf, sizeof(buf));/* 打开serve的文件 */resource = fopen(filename, "r");if (resource == NULL)not_found(client);else {/* 写http头 */headers(client, filename);/* 复制文件 */cat(client, resource);}fclose(resource);}

其中在服务上读取要访问的文件，并构造http响应格式，以响应客户端。其中，headers()完成响应头的构造，并把响应头信息发送给客户端。cat()函数则负责把访问的文件发送给客户端。

headers()代码如下:

/**********************************************************************//* Return the informational HTTP headers about a file. *//* Parameters: the socket to print the headers on *             the name of the file *//**********************************************************************/void headers(int client, const char *filename){char buf[1024];(void)filename;  /* could use filename to determine file type *//* 正常响应客户端 */strcpy(buf, "HTTP/1.0 200 OK\r\n");send(client, buf, strlen(buf), 0);strcpy(buf, SERVER_STRING);send(client, buf, strlen(buf), 0);sprintf(buf, "Content-Type: text/html\r\n");send(client, buf, strlen(buf), 0);strcpy(buf, "\r\n"); // 协议规定头部于实体的空行send(client, buf, strlen(buf), 0);}

cat()代码如下：

/**********************************************************************//* Put the entire contents of a file out on a socket.  This function * is named after the UNIX "cat" command, because it might have been * easier just to do something like pipe, fork, and exec("cat"). * Parameters: the client socket descriptor *             FILE pointer for the file to cat *//**********************************************************************/void cat(int client, FILE *resource){char buf[1024];/* 读取文件内容发送给客户端 */fgets(buf, sizeof(buf), resource);while (!feof(resource)) {send(client, buf, strlen(buf), 0);fgets(buf, sizeof(buf), resource);}}

执行CGI程序的代码如下：

/**********************************************************************//* Execute a CGI script.  Will need to set environment variables as * appropriate. * Parameters: client socket descriptor *             path to the CGI script *//**********************************************************************/void execute_cgi(int client, const char *path,                 const char *method, const char *query_string){char buf[1024];int cgi_output[2];int cgi_input[2];pid_t pid;int status;int i;char c;int numchars = 1;int content_length = -1;buf[0] = 'A'; buf[1] = '\0';if (strcasecmp(method, "GET") == 0) /* GET *//* 读取并丢弃请求headers */while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */numchars = get_line(client, buf, sizeof(buf));else {  /* POST */numchars = get_line(client, buf, sizeof(buf));while ((numchars > 0) && strcmp("\n", buf)) {buf[15] = '\0';if (strcasecmp(buf, "Content-Length:") == 0)content_length = atoi(&(buf[16]));numchars = get_line(client, buf, sizeof(buf));}if (content_length == -1) {bad_request(client);return;}}/* 正确，HTTP状态码200 */sprintf(buf, "HTTP/1.0 200 OK\r\n");send(client, buf, strlen(buf), 0);/* 创建两个管道，管道半双工, cig_output[0]读, cig_output[1]写 */if (pipe(cgi_output) < 0) {cannot_execute(client);return;}if (pipe(cgi_input) < 0) {cannot_execute(client);return;}if ( (pid = fork()) < 0 ) {cannot_execute(client);return;}if (pid == 0) { /* child: CGI script */char meth_env[255];char query_env[255];char length_env[255];/* 把STDOUT重定向到cgi_output的写入端 */ dup2(cgi_output[1], 1);/* 把STDIN重定向到cgi_input的读取端 */dup2(cgi_input[0], 0);/* 关闭cgi_input的写入端和cgi_output的读取端, 把半双工变单工通信 */close(cgi_output[0]);close(cgi_input[1]);/* 设置request_method的环境变量 */sprintf(meth_env, "REQUEST_METHOD=%s", method);putenv(meth_env);if (strcasecmp(method, "GET") == 0) {sprintf(query_env, "QUERY_STRING=%s", query_string);putenv(query_env);}else { /* POST *//* 设置content_length的环境变量 */ sprintf(length_env, "CONTENT_LENGTH=%d", content_length);putenv(length_env);}/* 用execl运行cgi程序 */execl(path, path, NULL);exit(0);}else {    /* parent *//* 关闭cgi_input的读取端和cgi_output的写入端 */close(cgi_output[1]);close(cgi_input[0]);/* 接收POST方法过来的数据 */if (strcasecmp(method, "POST") == 0)for (i = 0; i < content_length; i++) {recv(client, &c, 1, 0);/*把POST数据写入cgi_input，现在重定向到STDIN */ write(cgi_input[1], &c, 1);}/* 读取cgi_output的管道输出到客户端，该管道输入是STDOUT */while (read(cgi_output[0], &c, 1) > 0)send(client, &c, 1, 0);close(cgi_output[0]);close(cgi_input[1]);waitpid(pid, &status, 0);}}