tinyhttpd ------ C 语言实现最简单的 HTTP 服务器

工作流程：

1>服务器启动，在指定端口或随机选取端口绑定httpd服务。

2>收到一个http请求时(其实就是listen端口accept的时候)，派生一个线程运行accept_request函数。

3>取出http请求中method(get或post)和url,对于get方法，如果有携带参数，则query_string指针指向url中?后面的get参数。

4>格式化url到path数组，表示浏览器请求的文件路径，在tinyhttpd中服务器文件是在htdocs文件夹下。当url以/结尾，或者url是个目录，则默认在path中加上index.thml，表示访问主页。

5>如果文件路径合法，对于无参数的get请求，直接输出服务器文件到浏览器，即用http格式写到套接字上，跳到(10)。其他情况(带参数get，post方法，url为科执行文件)，则调用execute_cgi函数执行cgi脚本。

6>读取整个http请求并丢弃，如果是post则找出content-length，把http状态码200写到套接字里面。

7>建立两个管道，cgi_input和cgi_output,并fork一个子进程。

8>在子进程中，把stdout重定向到cgi_output的写入端，把stdin重定向到cgi_input的读取端，关闭cgi_input的写入端和cgi_output的读取端，是指request_method的环境变量，get的话设置query_string的环境变量，post的话设置content-length的环境变量，这些环境变量都是为了给cgi脚本调用，接着用execl运行cgi程序。

9>在父进程中，关闭cgi_input的读取端和cgi_output的写入端，如果post的话，把post数据写入到cgo_input，已被重定向到stdin读取cgi_output的管道输出到客户端，等待子进程结束。

10>关闭与浏览器的链接，完成一次http请求与回应，因为http是无连接的。

 /* 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);
 //处理从套接字上监听到的一个HTTP请求，在这里可以很大一部分的体现服务器处理请求的流程
 void bad_request(int);
 //返回给客户端这是个错误请求，HTTP状态码是400 BAD REQUEST
 void cat(int, FILE *);
 //读取服务器上某个文件写到socket套接字
 void cannot_execute(int);
 //主要执行在处理cgi程序的处理，也是个主要函数
 void error_die(const char *);
 //把错误信息写到perror并退出
 void execute_cgi(int, const char *, const char *, const char *);
 //运行cgi程序的处理，也是哥主函数
 int get_line(int, char *, int);
 //读取套接字的一行，把回车换行等情况都统一为换行符结束
 void headers(int, const char *);
 //把HTTP相应头写到套接字
 void not_found(int);
 //主要处理找不到请求的文件时的情况
 void serve_file(int, const char *);
 //调用cat把服务器文件返回给浏览器
 int startup(u_short *);
 //初始化httpd服务，包括建立套接字，绑定端口，进行监听等
 void unimplemented(int);
 //返回给浏览器表示接收到的http请求所用的method不被支持

 /**********************************************************************/
 /* 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;

     numchars = get_line(client, buf, sizeof(buf));
     //读取 client端发送的数据并且 返回的参数是 numchars
     i = ;
     j = ;
     while (!ISspace(buf[j]) && (i < sizeof(method) - ))
     {
         method[i] = buf[j];
         i++;
         j++;
     }
     //得到传递的参数是post 还是get方法 还是其他
     method[i] = '\0';

     if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))
     {
     //回给浏览器表明收到的 HTTP 请求所用的 method 不被支持
         unimplemented(client);
         return;
     }

     if (strcasecmp(method, "POST") == )
         cgi = ;

     i = ;
     //http请求行格式是 method urI http-version
     while (ISspace(buf[j]) && (j < sizeof(buf)))
         j++;
     while (!ISspace(buf[j]) && (i < sizeof(url) - ) && (j < sizeof(buf)))
     {
         url[i] = buf[j]; //包含请求行中的URI
         i++;
         j++;
     }
     url[i] = '\0';
     ///获取发送数据中的URI
     if (strcasecmp(method, "GET") == )
     {
     //get方法 是将参数传递在URI中的？后面如果元素多用&进行链接
         query_string = url;
         while ((*query_string != '?') && (*query_string != '\0'))
             query_string++;
          // get 请求？ 后面为参数
      if (*query_string == '?')
         {
             cgi = ;
             *query_string = '\0';
             query_string++;
         }
     }
     //格式url存储在path数组 并且html存储在 htdocs文件中
     sprintf(path, "htdocs%s", url);
     if (path[strlen(path) - ] == '/')
         strcat(path, "index.html");  //字符串进行衔接 + index.html
    //stat函数 根据path路径 获取文件内容 存储在 st 结构体中  成功返回0 错误返回-1
     if (stat(path, &st) == -)
     {
         while ((numchars > ) && strcmp("\n", buf))  /* read & discard headers */
             numchars = get_line(client, buf, sizeof(buf));
         not_found(client);
     }
     else
     {
         if ((st.st_mode & S_IFMT) == S_IFDIR)
             strcat(path, "/index.html");
         //文件的权限 属主 属组 其它 三种任一个拥有执行权
     if ((st.st_mode & S_IXUSR) ||
                 (st.st_mode & S_IXGRP) ||
                 (st.st_mode & S_IXOTH)    )
             cgi = ;
     //调用cat 把服务器文件返回给浏览器  post方法或者拥有执行权限
         if (!cgi)
             serve_file(client, path);
         else
             execute_cgi(client, path, method, query_string)
     //运行cgi程序的处理，也是个主要函数
     }

     close(client);
 }

 /**********************************************************************/
 /* Inform the client that a request it has made has a problem.
  * Parameters: client socket */
 /**********************************************************************/
 void bad_request(int client)
 {
     char buf[];

     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 */
 /**********************************************************************/
 //读取服务器上的某个文件 写到socket套接字上
 void cat(int client, FILE *resource)
 {
     char buf[];

     fgets(buf, sizeof(buf), resource);
     //检测流上的文件结束符  如果文件结束，则返回非0值，否则返回0，文件结束符只能被clearerr()清除。
     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[];

     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)
 {
     perror(sc);
     exit();
 }

 /**********************************************************************/
 /* Execute a CGI script.  Will need to set environment variables as
  * appropriate.
  * Parameters: client socket descriptor
  *             path to the CGI script */
 /**********************************************************************/

 //运行cgi程序  也是个主函数
 void execute_cgi(int client, const char *path,
                  const char *method, const char *query_string)
 {
     //在父进程中，关闭cgi_input的读入端和cgi_output的写入端，如果post的话
     //把post数据写入到cgi_input，已被重定向到stdin，读取cgi_output的管道
     //输出到客户端，该管道输入是stdout，接着关闭所有管道，等待子进程结束。

     char buf[];
     int cgi_output[];
     int cgi_input[];
     //cgi_output[1] cgi_input[1] 为输入端
     //cgi_input[0] cgi_output[0] 为输出端
     pid_t pid;
     int status;
     int i;
     char c;
     int numchars = ;
     int content_length = -;

     buf[] = 'A';
     buf[] = '\0';
     //读入请求头
     if (strcasecmp(method, "GET") == )
         while ((numchars > ) && strcmp("\n", buf))  /* read & discard headers */
             numchars = get_line(client, buf, sizeof(buf));
     else    /* POST */
     {
         numchars = get_line(client, buf, sizeof(buf));
         while ((numchars > ) && strcmp("\n", buf))
         {
             buf[] = '\0';
             if (strcasecmp(buf, "Content-Length:") == )
                 content_length = atoi(&(buf[]));
             numchars = get_line(client, buf, sizeof(buf));
         }
         if (content_length == -)
         {
             bad_request(client);
             return;
         }
     }

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

     if (pipe(cgi_output) < )
     {
         cannot_execute(client);
         return;
     }
     if (pipe(cgi_input) < )
     {
         cannot_execute(client);
         return;
     }

     if ( (pid = fork()) <  )
     {
         cannot_execute(client);
         return;
     }
     if (pid == )  /* child: CGI script */
     {
         char meth_env[];
         char query_env[];
         char length_env[];
     //把stdout重定向到cgi_output的写入端
         dup2(cgi_output[], );
     //把stdin重定向到cgi_input的读入端
         dup2(cgi_input[], );
     //关闭cgi_output的读入端 和 cgi_input的 写入端
         close(cgi_output[]);
         close(cgi_input[]);
     //设置request_method的环境变量
         sprintf(meth_env, "REQUEST_METHOD=%s", method);
         putenv(meth_env);
         if (strcasecmp(method, "GET") == )
         {
         //设置query_string的环境变量
             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();
     }
     else        /* parent */
     {
         close(cgi_output[]);
         close(cgi_input[]);
         //关闭cgi_output的 写入端 和 cgi_input的读取端
     if (strcasecmp(method, "POST") == )
        //接受post的数据
             for (i = ; i < content_length; i++)
             {
                 recv(client, &c, , );
                 write(cgi_input[], &c, );
                 //讲post数据写入cgi_input，并且重定向到stdin中
              }
     //读取cgi_output的管道输出到客户端，该管道输入时stdout
         while (read(cgi_output[], &c, ) > )
             send(client, &c, , );
     //关闭管道
         close(cgi_output[]);
         close(cgi_input[]);
         //等待子进程
     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;

     while ((i < size - ) && (c != '\n'))
     {
         //每次接受一个字符
     n = recv(sock, &c, , );
         /* DEBUG printf("%02X\n", c); */
         if (n > )
         {
             if (c == '\r')
             {
                 n = recv(sock, &c, , MSG_PEEK);
                 /* DEBUG printf("%02X\n", c); */
                 if ((n > ) && (c == '\n'))
                     recv(sock, &c, , );
                 else
                     c = '\n';
             }
             buf[i] = c;
             i++;
         }
         else
             c = '\n';
     }
     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 */
 /**********************************************************************/
 //http 响应体
 void headers(int client, const char *filename)
 {
     char buf[];
     (void)filename;  /* could use filename to determine file type */

     strcpy(buf, "HTTP/1.0 200 OK\r\n");//响应的状态行
     send(client, buf, strlen(buf), );
     strcpy(buf, SERVER_STRING);
     send(client, buf, strlen(buf), );
     sprintf(buf, "Content-Type: text/html\r\n"); //响应头
     send(client, buf, strlen(buf), );
     strcpy(buf, "\r\n");        //响应正文段
     send(client, buf, strlen(buf), );
 }

 /**********************************************************************/
 /* Give a client a 404 not found status message. */
 /**********************************************************************/
 void not_found(int client)
 {
     //客户端发送的请求无法实现
     char buf[];
    //响应行
     sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, SERVER_STRING);
     send(client, buf, strlen(buf), );
     //响应头
     sprintf(buf, "Content-Type: text/html\r\n");
     send(client, buf, strlen(buf), );
     sprintf(buf, "\r\n");
     //响应头和响应正文段之间有一个空行 表示响应行结束
     send(client, buf, strlen(buf), );
     //响应正文段 text/html
     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[];

     buf[] = 'A';
     buf[] = '\0';
     while ((numchars > ) && strcmp("\n", buf))  /* read & discard headers */
         numchars = get_line(client, buf, sizeof(buf));

     resource = fopen(filename, "r");
     if (resource == NULL)
         not_found(client);
     else
     {
         headers(client, filename);
         cat(client, resource);
     }
     fclose(resource);
 }

 /**********************************************************************/
 /* This function starts the process of listening for web connections
  * on a specified port.  If the port is 0, then dynamically allo        //响应正文段cate 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;
     //建立套接字
     httpd = socket(PF_INET, SOCK_STREAM, );
     if (httpd == -)
         error_die("socket");
     memset(&name, , sizeof(name));
     name.sin_family = AF_INET;
     name.sin_port = htons(*port);
     name.sin_addr.s_addr = htonl(INADDR_ANY);
     //绑定端口和ip
     if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < )
         error_die("bind");
     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);
     }
     //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)
 {
     //发回响应信息  http的请求方法不被接受
     char buf[];
     //返回501 错误 未实现 (Not implemented)是指Web 服务器不理解或不支持发送给它的 HTTP 数据流中找到的 HTTP 方法
     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");//响应头
     send(client, buf, strlen(buf), );
     sprintf(buf, "\r\n");
     send(client, buf, strlen(buf), ); //响应正文段
     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 ()
     {
         client_sock = accept(server_sock,
                              (struct sockaddr *)&client_name,
                              &client_name_len);
         //建立链接
     if (client_sock == -)
             error_die("accept");
         /* accept_request(client_sock); */
         //多线程进行控制
     if (pthread_create(&newthread , NULL, accept_request, client_sock) != )
             perror("pthread_create");
     }

     close(server_sock);

     return();
 }