源码分析之tinyhttpd-0.1

1. 简介：

tinyhttpd是使用c语言开发的超轻量级http服务器，通过代码流程可以了解http服务器的基本处理流程，

并且涉及了网络套接字，线程，父子进程，管道等等知识点；

项目地址：http://sourceforge.net/projects/tinyhttpd/

2. 流程介绍：

(1) 服务器启动，等待客户端请求到来；

(2) 客户端请求到来，创建新线程处理该请求；

(3) 读取httpHeader中的method，截取url，其中GET方法需要记录url问号之后的参数串;

(4) 根据url构造完整路径，如果是/结尾，则指定为该目录下的index.html;

(5) 获取文件信息，如果找不到文件，返回404，找到文件则判断文件权限；

(6) 如果是GET请求并且没有参数，或者文件不可执行，则直接将文件内容构造http信息返回给客户端；

(7) 如果是GET带参数，POST，文件可执行，则执行CGI；

(8) GET请求略过httpHeader，POST方法需要记录httpHeader中的Content-Length:xx；

(9) 创建管道用于父子进程通信，fork产生子进程；

(10) 子进程设置环境变量，将标准输入和输出与管道相连，并且通过exec执行CGI；

(11) 如果是POST，父进程将读到post内容发送给子进程，并且接收子进程的输出，输出给客户端；

3. 管道说明：

4. 代码注释：

 /* 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"

 void accept_request(int);
 void bad_request(int);
 void cat(int, FILE *);
 void cannot_execute(int);
 void error_die(const char *);
 void execute_cgi(int, const char *, const char *, const char *);
 int get_line(int, char *, int);
 void headers(int, const char *);
 void not_found(int);
 void serve_file(int, const char *);
 int startup(u_short *);
 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[];
     int numchars;
     char method[];
     char url[];
     char path[];
     size_t i, j;
     struct stat st;
     int cgi = ;      /* becomes true if server decides this is a CGI
                * program */
     char *query_string = NULL;

     //读取第一行数据
     numchars = get_line(client, buf, sizeof(buf));
     i = ; j = ;
     //读取http的头部method字段，读到空白为止
     while (!ISspace(buf[j]) && (i < sizeof(method) - ))
     {
         method[i] = buf[j];
         i++; j++;
     }
     method[i] = '\0';

     //只支持GET和POST请求，其他请求方式返回未实现
     if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
     {
         unimplemented(client);
         return;
     }
     //如果是POST请求，设置cgi标志为1
     if (strcasecmp(method, "POST") == )
         cgi = ;

     i = ;
     //跳过空白字符
     while (ISspace(buf[j]) && (j < sizeof(buf)))
         j++;
     //读取url字串
     while (!ISspace(buf[j]) && (i < sizeof(url) - ) && (j < sizeof(buf)))
     {
         url[i] = buf[j];
         i++; j++;
     }
     url[i] = '\0';
     //如果是GET请求，需要从url中解析参数
     if (strcasecmp(method, "GET") == )
     {
         query_string = url;
         //找到?位置
         while ((*query_string != '?') && (*query_string != '\0'))
             query_string++;
         //当前字符为?字符
         if (*query_string == '?')
         {
             cgi = ; //标记cgi字段
             *query_string = '\0'; //将?替换成\0
             query_string++; //query_string指向get参数
         }
     }
     //连接url资源路径
     sprintf(path, "htdocs%s", url);
     //如果访问的是/结尾的目录，那么指定为目录下的index.html
     if (path[strlen(path) - ] == '/')
         strcat(path, "index.html");
     //获取文件信息失败
     if (stat(path, &st) == -) {
         //将header中的信息都丢弃
         while ((numchars > ) && strcmp("\n", buf))  /* read & discard headers */
             numchars = get_line(client, buf, sizeof(buf));
         //返回404
         not_found(client);
     }
     else
     {
         //如果访问的是目录，那么指定为目录下的index.html
         if ((st.st_mode & S_IFMT) == S_IFDIR)
             strcat(path, "/index.html");
         //如果具有可执行权限，标记cgi
         if ((st.st_mode & S_IXUSR) ||
                 (st.st_mode & S_IXGRP) ||
                 (st.st_mode & S_IXOTH)    )
             cgi = ;
         //不需要cgi参与的文件直接进行服务
         if (!cgi)
             serve_file(client, path);
         //否则执行cgi
         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[];
     //发送BAD REQUEST提示信息到客户端
     sprintf(buf, "HTTP/1.0 400 BAD REQUEST\r\n");
     send(client, buf, sizeof(buf), );
     sprintf(buf, "Content-type: text/html\r\n");
     send(client, buf, sizeof(buf), );
     sprintf(buf, "\r\n");
     send(client, buf, sizeof(buf), );
     sprintf(buf, "<P>Your browser sent a bad request, ");
     send(client, buf, sizeof(buf), );
     sprintf(buf, "such as a POST without a Content-Length.\r\n");
     send(client, buf, sizeof(buf), );
 }

 /**********************************************************************/
 /* 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[];
     //循环读取并发送文件内容
     fgets(buf, sizeof(buf), resource);
     while (!feof(resource))
     {
         send(client, buf, strlen(buf), );
         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[];
     //发送500服务器内部错误到客户端
     sprintf(buf, "HTTP/1.0 500 Internal Server Error\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "Content-type: text/html\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "<P>Error prohibited CGI execution.\r\n");
     send(client, buf, strlen(buf), );
 }

 /**********************************************************************/
 /* 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)
 {
     //打印错误信息并退出
     perror(sc);
     exit();
 }

 /**********************************************************************/
 /* 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[];
     int cgi_output[];
     int cgi_input[];
     pid_t pid;
     int status;
     int i;
     char c;
     int numchars = ;
     int content_length = -;

     buf[] = 'A'; buf[] = '\0';
     //如果是GET请求则读取并丢掉头部信息
     if (strcasecmp(method, "GET") == )
         while ((numchars > ) && strcmp("\n", buf))  /* read & discard headers */
             numchars = get_line(client, buf, sizeof(buf));
     //如果是POST请求
     else    /* POST */
     {
         //读取一行数据
         numchars = get_line(client, buf, sizeof(buf));
         while ((numchars > ) && strcmp("\n", buf))
         {
             //截取Content-Length:字段
             buf[] = '\0';
             //如果找到该字段，将该字段后面的字串转成整数长度
             if (strcasecmp(buf, "Content-Length:") == )
                 content_length = atoi(&(buf[]));
             //读取头部内容
             numchars = get_line(client, buf, sizeof(buf));
         }
         //没有找到Content-Length，发送bad request
         if (content_length == -) {
             bad_request(client);
             return;
         }
     }
     //发送http200头
     sprintf(buf, "HTTP/1.0 200 OK\r\n");
     send(client, buf, strlen(buf), );
     //创建输出管道，构造父子进程通信
     if (pipe(cgi_output) < ) {
         cannot_execute(client);
         return;
     }
     //创建输入管道，构造父子进程通信
     if (pipe(cgi_input) < ) {
         cannot_execute(client);
         return;
     }
     //创建子进程
     if ( (pid = fork()) <  ) {
         cannot_execute(client);
         return;
     }
     //子进程执行CGI脚本
     if (pid == )  /* child: CGI script */
     {
         char meth_env[];
         char query_env[];
         char length_env[];

         //子进程的标准输入输出与管道对接
         dup2(cgi_output[], ); //将标准输出重定向到cgi输出管道的写端
         dup2(cgi_input[], ); //将标准输入重定向到cgi输入管道的读端

         close(cgi_output[]); //关闭cgi输出管道的读端
         close(cgi_input[]); //关闭cgi输入管道的写端
         //设置method环境变量
         sprintf(meth_env, "REQUEST_METHOD=%s", method);
         putenv(meth_env);
         //如果是GET方式设置请求参数环境变量
         if (strcasecmp(method, "GET") == ) {
             sprintf(query_env, "QUERY_STRING=%s", query_string);
             putenv(query_env);
         }
         //如果是POST方式设置内容长度环境变量
         else {   /* POST */
             sprintf(length_env, "CONTENT_LENGTH=%d", content_length);
             putenv(length_env);
         }
         //执行CGI
         execl(path, path, NULL);
         exit();
     } else {    /* parent */
         close(cgi_output[]); //关闭cgi输出管道的写端
         close(cgi_input[]); //关闭cgi输入管道的读端
         //如果是POST请求，循环读取post内容，并且输入到cgi子进程
         if (strcasecmp(method, "POST") == )
             for (i = ; i < content_length; i++) {
                 recv(client, &c, , );
                 write(cgi_input[], &c, );
             }
         //从cgi中循环读取输出内容，发送到客户端
         while (read(cgi_output[], &c, ) > )
             send(client, &c, , );

         //关闭管道
         close(cgi_output[]);
         close(cgi_input[]);
         //等待子进程结束
         waitpid(pid, &status, );
     }
 }

 /**********************************************************************/
 /* 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 = ;
     char c = '\0';
     int n;
     //接收\n结束的一行数据或接收满缓冲区
     while ((i < size - ) && (c != '\n'))
     {
         //接收一个字节
         n = recv(sock, &c, , );
         /* DEBUG printf("%02X\n", c); */
         if (n > )
         {
             //如果接收到了\r符号
             if (c == '\r')
             {
                 //将下一个字字符预取出来，注意MSG_PEEK本地接收窗口不滑动，下次读取仍然可以读取到该字符
                 n = recv(sock, &c, , MSG_PEEK);
                 /* DEBUG printf("%02X\n", c); */
                 //如果下一个字符是\n的话，那么接收这个字符
                 if ((n > ) && (c == '\n'))
                     recv(sock, &c, , );
                 //不是\n的话，那么将\r替换成\n
                 else
                     c = '\n';
             }
             //字符存入buf，继续读取
             buf[i] = c;
             i++;
         }
         else
             c = '\n';
     }
     //设置buf字符串结束符
     buf[i] = '\0';

     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[];
     (void)filename;  /* could use filename to determine file type */
     //发送http头 http码 服务器信息 内容类型等头部信息
     strcpy(buf, "HTTP/1.0 200 OK\r\n");
     send(client, buf, strlen(buf), );
     strcpy(buf, SERVER_STRING);
     send(client, buf, strlen(buf), );
     sprintf(buf, "Content-Type: text/html\r\n");
     send(client, buf, strlen(buf), );
     strcpy(buf, "\r\n");
     send(client, buf, strlen(buf), );
 }

 /**********************************************************************/
 /* Give a client a 404 not found status message. */
 /**********************************************************************/
 void not_found(int client)
 {
     char buf[];
     //发送http头 http码 服务器信息 内容类型等头部信息 html提示信息
     sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, SERVER_STRING);
     send(client, buf, strlen(buf), );
     sprintf(buf, "Content-Type: text/html\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "<HTML><TITLE>Not Found</TITLE>\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "<BODY><P>The server could not fulfill\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "your request because the resource specified\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "is unavailable or nonexistent.\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "</BODY></HTML>\r\n");
     send(client, buf, strlen(buf), );
 }

 /**********************************************************************/
 /* 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 = ;
     char buf[];

     //读取丢弃所有头部信息
     buf[] = 'A'; buf[] = '\0';
     while ((numchars > ) && strcmp("\n", buf))  /* read & discard headers */
         numchars = get_line(client, buf, sizeof(buf));

     //打开资源文件
     resource = fopen(filename, "r");
     //打开失败，发送404
     if (resource == NULL)
         not_found(client);
     else
     {
         headers(client, filename); //发送http头
         cat(client, resource); //发送资源文件内容
     }
     //关闭资源文件
     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 = ;
     struct sockaddr_in name;
     //创建tcp socket
     httpd = socket(PF_INET, SOCK_STREAM, );
     if (httpd == -)
         error_die("socket");
     memset(&name, , sizeof(name));
     //设置sockaddr地址结构
     name.sin_family = AF_INET;
     name.sin_port = htons(*port);
     name.sin_addr.s_addr = htonl(INADDR_ANY);
     //绑定到本地地址port指定端口
     if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < )
         error_die("bind");
     //如果没有指定端口，则由系统指定，此处或得到系统指定的端口
     if (*port == )  /* if dynamically allocating a port */
     {
         int namelen = sizeof(name);
         if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -)
             error_die("getsockname");
         *port = ntohs(name.sin_port);
     }
     //服务器开始监听
     if (listen(httpd, ) < )
         error_die("listen");
     return(httpd);
 }

 /**********************************************************************/
 /* Inform the client that the requested web method has not been
  * implemented.
  * Parameter: the client socket */
 /**********************************************************************/
 void unimplemented(int client)
 {
     char buf[];
     //发送未实现的请求方法和提示消息给客户端
     sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, SERVER_STRING);
     send(client, buf, strlen(buf), );
     sprintf(buf, "Content-Type: text/html\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implemented\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "</TITLE></HEAD>\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "<BODY><P>HTTP request method not supported.\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "</BODY></HTML>\r\n");
     send(client, buf, strlen(buf), );
 }

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

 int main(void)
 {
     int server_sock = -;
     u_short port = ;
     int client_sock = -;
     struct sockaddr_in client_name;
     int client_name_len = sizeof(client_name);
     pthread_t newthread;

     server_sock = startup(&port);
     printf("httpd running on port %d\n", port);

     while ()
     {
         //等待客户端连接到来
         client_sock = accept(server_sock,
                 (struct sockaddr *)&client_name,
                 &client_name_len);
         if (client_sock == -)
             error_die("accept");
         /* accept_request(client_sock); */
         //开启一个新线程处理客户端请求
         if (pthread_create(&newthread , NULL, accept_request, client_sock) != )
             perror("pthread_create");
     }
     //关闭服务器
     close(server_sock);

     return();
 }