Tinyhttp源码详解(带注释)


/* J. David's webserver */

/* This is a simple webserver.

 * Created November 1999 by J. David Blackstone.

 * CSE 4344 (Network concepts), Prof. Zeigler

 * University of Texas at Arlington

 */

/* This program compiles for Sparc Solaris 2.6.

 * To compile for Linux:

 *  1) Comment out the #include <pthread.h> line.

 *  2) Comment out the line that defines the variable newthread.

 *  3) Comment out the two lines that run pthread_create().

 *  4) Uncomment the line that runs accept_request().

 *  5) Remove -lsocket from the Makefile.

 */

#include <stdio.h>

#include <sys/socket.h>

#include <sys/types.h>

#include <netinet/in.h>

#include <arpa/inet.h>

#include <unistd.h>

#include <ctype.h>

#include <strings.h>

#include <string.h>

#include <sys/stat.h>

#include <pthread.h>

#include <sys/wait.h>

#include <stdlib.h>

 

#define ISspace(x) isspace((int)(x))

 

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"

 

// 接受请求,并处理

void accept_request(int clientsockfd);

// 无法处理请求,回写400到client

void bad_request(int);

// 将文件内容发送到client

void cat(int client, FILE* fp);

// 不可以执行CGI程序,回写500到client

void cannot_execute(int);

// 输出错误信息

void error_die(const char *);

// 执行cgi程序

void execute_cgi(int, const char *, const char *, const char *);

// 从fd中读取一行,并将读取的'\r\n'和'\r'转换为'\n'

int get_line(int fd, char* buf, int bufsize);

// 返回200 OK给客户端

void headers(int clientsockfd, const char * filename);

// 返回404状态给客户端

void not_found(int);

// 处理客户端文件请求,发送404或200+文件内容到client

void serve_file(int client, const char* filename);

// 开启soket监听

int startup(u_short *);

// 返回501状态给客户端

void unimplemented(int);

 

/**********************************************************************/

/* 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];	// 方法(请求类型)

	char	url[255];		// 请求的资源URL

	char	path[512];		// 请求资源的本地路径

	size_t i, j;

	struct stat st;

	int cgi = 0;		/* becomes true if server decides this is a CGI program */

						/* 为真时,表示服务器需调用一个CGI程序 */

 

	char *query_string = NULL;

	// 1. 从客户端连接请求数据包中读取一行

	numchars = get_line(client, buf, sizeof(buf));

	// 2. 从读取的数据中提取出请求类型

	i = 0; j = 0;

	while (!ISspace(buf[j]) && (i < sizeof(method) - 1))

	{

		method[i] = buf[j];

		i++; j++;

	}

	method[i] = '\0';

	// 3. 判断请求类型

	if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))

	{

		unimplemented(client);	// 不支持请求类型,向客户端返回501

		return;

	}

 

	if (strcasecmp(method, "POST") == 0){

		cgi = 1;	// 如果是POST请求,调用cgi程序

	}

 

	// 4. 提取请求的资源URL

	i = 0;

	while (ISspace(buf[j]) && (j < sizeof(buf))){

		j++;	// 定位下一个非空格位置

	}

	while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))

	{

		url[i] = buf[j];

		i++; j++;

	}

	url[i] = '\0';

 

	if (strcasecmp(method, "GET") == 0)

	{

		query_string = url;	// 为GET请求,查询语句为url

		// 如果查询语句中含义'?',查询语句为'?'字符后面部分

		while ((*query_string != '?') && (*query_string != '\0')){

			query_string++;

		}

		if (*query_string == '?')

		{

			cgi = 1;

			*query_string = '\0';	// 从'?'处截断,前半截为url

			query_string++;

		}

	}

 

	// 5. 生成本地路径

	sprintf(path, "htdocs%s", url);

	if (path[strlen(path) - 1] == '/'){

		strcat(path, "index.html");	//如果请求url是以'/'结尾,则指定为该目录下的index.html文件

	}

	// 6. 判断请求资源的状态

	if (stat(path, &st) == -1) {

		// 从client中读取,直到遇到两个换行(起始行startline和首部header之间间隔)

		while ((numchars > 0) && strcmp("\n", buf)){  /* read & discard headers */

			numchars = get_line(client, buf, sizeof(buf));

		}

		not_found(client);	// 501

	}

	else

	{

		// 请求的是个目录,指定为该目录下的index.html文件

		if ((st.st_mode & S_IFMT) == S_IFDIR){

			strcat(path, "/index.html");

		}

		// 请求的是一个可执行文件,作为CGI程序

		if ((st.st_mode & S_IXUSR) ||

			(st.st_mode & S_IXGRP) ||

			(st.st_mode & S_IXOTH)    ){

		  cgi = 1;

		}

		// 判断是执行一个CGI程序还是返回一个文件内容给客户端

		if (!cgi){

		  serve_file(client, path);	// 

		}

		else{

		  execute_cgi(client, path, method, query_string);

		}

	}

 

	close(client);

}

 

/**********************************************************************/

/* Inform the client that a request it has made has a problem.

 * Parameters: client socket */

/**********************************************************************/

void bad_request(int client)

{

	char buf[1024];

	// 向client回写400状态

	sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");

	send(client, buf, sizeof(buf), 0);

	sprintf(buf, "Content-type: text/html\r\n");

	send(client, buf, sizeof(buf), 0);

	sprintf(buf, "\r\n");

	send(client, buf, sizeof(buf), 0);

	sprintf(buf, "<P>Your browser sent a bad request, ");

	send(client, buf, sizeof(buf), 0);

	sprintf(buf, "such as a POST without a Content-Length.\r\n");

	send(client, buf, sizeof(buf), 0);

}

 

/**********************************************************************/

/* 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];

	// 从resource中读取一行

	fgets(buf, sizeof(buf), resource);

	// 将文件中的内容发送到客户端

	while (!feof(resource))

	{

		send(client, buf, strlen(buf), 0);

		fgets(buf, sizeof(buf), resource);

	}

}

 

/**********************************************************************/

/* Inform the client that a CGI script could not be executed.

 * Parameter: the client socket descriptor. */

/**********************************************************************/

void cannot_execute(int client)

{

	char buf[1024];

	// 向客户端回写500状态,不可以执行CGI程序

	sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "Content-type: text/html\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "<P>Error prohibited CGI execution.\r\n");

	send(client, buf, strlen(buf), 0);

}

 

/**********************************************************************/

/* Print out an error message with perror() (for system errors; based

 * on value of errno, which indicates system call errors) and exit the

 * program indicating an error. */

/**********************************************************************/

void error_die(const char *sc)

{

	perror(sc);	// 输出错误信息

	exit(1);	// 退出程序

}

 

/********************************************************************//*

 * @brief	执行一个CGI脚本.可能需要设置适当的环境变量.

 * @prama	client	客户端socket文件描述符

 * @prama	path	CGI 脚本路径

 * @prama	method	请求类型

 * @prama	query_string	查询语句

 **********************************************************************/

void execute_cgi(int client, const char *path,

			const char *method, const char *query_string)

{

	char	buf[1024];

	int		cgi_output[2];	// CGI程序输出管道

	int		cgi_input[2];	// CGI程序输入管道

 

	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){

		// 从client中读取,直到遇到两个换行

		while ((numchars > 0) && strcmp("\n", buf)){  /* read & discard headers */

			numchars = get_line(client, buf, sizeof(buf));

		}

	}

	else    /* POST */

	{

		// 获取请求主体的长度

		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;

		}

	}

 

	// 向client回写200 OK

	sprintf(buf, "HTTP/1.0 200 OK\r\n");

	send(client, buf, strlen(buf), 0);

 

	// 创建两个匿名管道

	if (pipe(cgi_output) < 0) {

		cannot_execute(client);

		return;

	}

	if (pipe(cgi_input) < 0) {

		cannot_execute(client);

		return;

	}

 

	// 创建子进程,去执行CGI程序

	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];

 

		dup2(cgi_output[1], 1);	//复制cgi_output[1](读端)到子进程的标准输出

		dup2(cgi_input[0], 0);	//复制cgi_input[0](写端)到子进程的标准输入

		close(cgi_output[0]);	//关闭多余文件描述符

		close(cgi_input[1]);

 

		sprintf(meth_env, "REQUEST_METHOD=%s", method);

		putenv(meth_env);	// 添加一个环境变量

 

		if (strcasecmp(method, "GET") == 0) {

			sprintf(query_env, "QUERY_STRING=%s", query_string);

			putenv(query_env);

		}

		else {   /* POST */

			sprintf(length_env, "CONTENT_LENGTH=%d", content_length);

			putenv(length_env);

		}

		// 执行CGI程序

		execl(path, path, NULL);

		exit(0);	// 子进程退出

	}

	else 

	{    /* parent */

		close(cgi_output[1]);	// 关闭cgi_output读端

		close(cgi_input[0]);	// 关闭cgi_input写端

 

		if (strcasecmp(method, "POST") == 0){

			// 请求类型为POST的时候,将POST数据包的主体entity-body部分

			// 通过cgi_input[1](写端)写入到CGI的标准输入

			for (i = 0; i < content_length; i++) {

				recv(client, &c, 1, 0);

				write(cgi_input[1], &c, 1);

			}

		}

		// 读取CGI的标准输出,发送到客户端

		while (read(cgi_output[0], &c, 1) > 0){

		  send(client, &c, 1, 0);

		}

		// 关闭多余文件描述符

		close(cgi_output[0]);

		close(cgi_input[1]);

		// 等待子进程结束

		waitpid(pid, &status, 0);

	}

}

 

/**********************************************************************/

/* 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;

 

	while ((i < size - 1) && (c != '\n'))

	{

		// 从sock中读取一个字节

		n = recv(sock, &c, 1, 0);

		/* DEBUG printf("%02X\n", c); */

		if (n > 0)

		{

			// 将 \r\n 或 \r 转换为'\n'

			if (c == '\r')

			{

				// 读到了'\r'就再预读一个字节

				n = recv(sock, &c, 1, MSG_PEEK);

				/* DEBUG printf("%02X\n", c); */

				// 如果读取到的是'\n',就读取,否则c='\n'

				if ((n > 0) && (c == '\n'))

				  recv(sock, &c, 1, 0);

				else

				  c = '\n';

			}

			// 读取数据放入buf

			buf[i] = c;

			i++;

		}

		else{

		  c = '\n';

		}

	}

	buf[i] = '\0';

	// 返回写入buf的字节数

	return(i);

}

 

/**********************************************************************/

/* 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 */

	

	// 向客户端回写200应答

	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");

	send(client, buf, strlen(buf), 0);

}

 

/**********************************************************************/

/* Give a client a 404 not found status message. */

/**********************************************************************/

void not_found(int client)

{

	char buf[1024];

	// 向client回写404状态

	sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, SERVER_STRING);

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "Content-Type: text/html\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "<BODY><P>The server could not fulfill\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "your request because the resource specified\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "is unavailable or nonexistent.\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "</BODY></HTML>\r\n");

	send(client, buf, strlen(buf), 0);

}

 

/**********************************************************************/

/* 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];

 

	buf[0] = 'A'; buf[1] = '\0';

	// 从client中读取,直到遇到两个换行(起始行start line和首部header的间隔)

	while ((numchars > 0) && strcmp("\n", buf)){  /* read & discard headers */

		numchars = get_line(client, buf, sizeof(buf));

	}

	// 

	resource = fopen(filename, "r");

	if (resource == NULL)

		not_found(client);	// 404错误

	else

	{

		headers(client, filename);	// 向客户端回写200 OK

		cat(client, resource);		// 将resource指向文件中的内容写入client

	}

	fclose(resource);

}

 

/**********************************************************************/

/* 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;

	// 创建一个socket

	httpd = socket(PF_INET, SOCK_STREAM, 0);

	if (httpd == -1){

		error_die("socket");

	}

	// 填写绑定地址

	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到指定地址

	if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0){

		error_die("bind");

	}

	// 如果采用随机分配端口,获取它

	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,等待连接

	if (listen(httpd, 5) < 0)

	  error_die("listen");

	// 返回正在监听的文件描述符

	return(httpd);

}

 

/**********************************************************************/

/* Inform the client that the requested web method has not been

 * implemented.

 * Parameter: the client socket */

/**********************************************************************/

void unimplemented(int client)

{

	char buf[1024];

	// 向client回写501状态

	sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, SERVER_STRING);

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "Content-Type: text/html\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "</TITLE></HEAD>\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");

	send(client, buf, strlen(buf), 0);

	sprintf(buf, "</BODY></HTML>\r\n");

	send(client, buf, strlen(buf), 0);

}

 

/**********************************************************************/

 

int main(void)

{

	int server_sock = -1;

	u_short port	= 0;	// 使用随机端口

	int client_sock = -1;

	struct sockaddr_in client_name;

	int client_name_len = sizeof(client_name);

	pthread_t newthread;

	

	// 启动服务,监听,等待连接

	server_sock = startup(&port);

	printf("httpd running on port %d\n", port);

 

	while (1)

	{

		// 接受请求

		client_sock = accept(server_sock,

					(struct sockaddr *)&client_name,

					&client_name_len);

		if (client_sock == -1)

			error_die("accept");

		// 创建一个线程来处理请求

		/* accept_request(client_sock); */

		if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)

			perror("pthread_create");

	}

	// 关闭

	close(server_sock);

 

	return(0);

}

 

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