/* 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[1024];  
    int numchars;  
    char method[255];  
    char url[255];  
    char 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;  
  
    /*得到请求的第一行*/  
    numchars = get_line(client, buf, sizeof(buf));  
    i = 0; j = 0;  
    /*把客户端的请求方法存到 method 数组*/  
    while (!ISspace(buf[j]) && (i < sizeof(method) - 1))  
    {  
        method[i] = buf[j];  
        i++; j++;  
    }  
    method[i] = '\0';  
  
    /*如果既不是 GET 又不是 POST 则无法处理 */  
    if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))  
    {  
        unimplemented(client);  
        return;  
    }  
  
    /* POST 的时候开启 cgi */  
    if (strcasecmp(method, "POST") == 0)  
        cgi = 1;  
  
    /*读取 url 地址*/  
    i = 0;  
    while (ISspace(buf[j]) && (j < sizeof(buf)))  
        j++;  
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < sizeof(buf)))  
    {  
        /*存下 url */  
        url[i] = buf[j];  
        i++; j++;  
    }  
    url[i] = '\0';  
  
    /*处理 GET 方法*/  
    if (strcasecmp(method, "GET") == 0)  
    {  
        /* 待处理请求为 url */  
        query_string = url;  
        while ((*query_string != '?') && (*query_string != '\0'))  
            query_string++;  
        /* GET 方法特点，? 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 文件都在 htdocs 中*/  
    sprintf(path, "htdocs%s", url);  
    /*默认情况为 index.html */  
    if (path[strlen(path) - 1] == '/')  
        strcat(path, "index.html");  
    /*根据路径找到对应文件 */  
    if (stat(path, &st) == -1) {  
        /*把所有 headers 的信息都丢弃*/  
        while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */  
            numchars = get_line(client, buf, sizeof(buf));  
        /*回应客户端找不到*/  
        not_found(client);  
    }  
    else  
    {  
        /*如果是个目录，则默认使用该目录下 index.html 文件*/  
        if ((st.st_mode & S_IFMT) == S_IFDIR)  
            strcat(path, "/index.html");  
      if ((st.st_mode & S_IXUSR) || (st.st_mode & S_IXGRP) || (st.st_mode & S_IXOTH)    )  
          cgi = 1;  
      /*不是 cgi,直接把服务器文件返回，否则执行 cgi */  
      if (!cgi)  
          serve_file(client, path);  
      else  
          execute_cgi(client, path, method, query_string);  
    }  
  
    /*断开与客户端的连接（HTTP 特点：无连接）*/  
    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];  
  
    /*回应客户端错误的 HTTP 请求 */  
    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];  
  
    /*读取文件中的所有数据写到 socket */  
    fgets(buf, sizeof(buf), resource);  
    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];  
  
    /* 回应客户端 cgi 无法执行*/  
    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)  
{  
    /*出错信息处理 */  
    perror(sc);  
    exit(1);  
}  
  
/**********************************************************************/  
/* 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)  
        /*把所有的 HTTP header 读取并丢弃*/  
        while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */  
            numchars = get_line(client, buf, sizeof(buf));  
    else    /* POST */  
    {  
        /* 对 POST 的 HTTP 请求中找出 content_length */  
        numchars = get_line(client, buf, sizeof(buf));  
        while ((numchars > 0) && strcmp("\n", buf))  
        {  
            /*利用 \0 进行分隔 */  
            buf[15] = '\0';  
            /* HTTP 请求的特点*/  
            if (strcasecmp(buf, "Content-Length:") == 0)  
                content_length = atoi(&(buf[16]));  
            numchars = get_line(client, buf, sizeof(buf));  
        }  
        /*没有找到 content_length */  
        if (content_length == -1) {  
            /*错误请求*/  
            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);  
  
    /* 建立管道*/  
    if (pipe(cgi_output) < 0) {  
        /*错误处理*/  
        cannot_execute(client);  
        return;  
    }  
    /*建立管道*/  
    if (pipe(cgi_input) < 0) {  
        /*错误处理*/  
        cannot_execute(client);  
        return;  
    }  
  
    if ((pid = fork()) < 0 ) {  
        /*错误处理*/  
        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 */  
        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) {  
            /*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(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]);  
        if (strcasecmp(method, "POST") == 0)  
            /*接收 POST 过来的数据*/  
            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);  
  
        /*关闭管道*/  
        close(cgi_output[0]);  
        close(cgi_input[1]);  
        /*等待子进程*/  
        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;  
  
    /*把终止条件统一为 \n 换行符，标准化 buf 数组*/  
    while ((i < size - 1) && (c != '\n'))  
    {  
        /*一次仅接收一个字节*/  
        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')  
            {  
                /*使用 MSG_PEEK 标志使下一次读取依然可以得到这次读取的内容，可认为接收窗口不滑动*/  
                n = recv(sock, &c, 1, MSG_PEEK);  
                /* DEBUG printf("%02X\n", c); */  
                /*但如果是换行符则把它吸收掉*/  
                if ((n > 0) && (c == '\n'))  
                    recv(sock, &c, 1, 0);  
                else  
                    c = '\n';  
            }  
            /*存到缓冲区*/  
            buf[i] = c;  
            i++;  
        }  
        else  
            c = '\n';  
    }  
    buf[i] = '\0';  
  
    /*返回 buf 数组大小*/  
    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 */  
  
    /*正常的 HTTP header */  
    strcpy(buf, "HTTP/1.0 200 OK\r\n");  
    send(client, buf, strlen(buf), 0);  
    /*服务器信息*/  
    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];  
  
    /* 404 页面 */  
    sprintf(buf, "HTTP/1.0 404 NOT FOUND\r\n");  
    send(client, buf, strlen(buf), 0);  
    /*服务器信息*/  
    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];  
  
    /*读取并丢弃 header */  
    buf[0] = 'A'; buf[1] = '\0';  
    while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */  
        numchars = get_line(client, buf, sizeof(buf));  
  
    /*打开 sever 的文件*/  
    resource = fopen(filename, "r");  
    if (resource == NULL)  
        not_found(client);  
    else  
    {  
        /*写 HTTP header */  
        headers(client, filename);  
        /*复制文件*/  
        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 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);  
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)  
        error_die("bind");  
    /*如果当前指定端口是 0，则动态随机分配一个端口*/  
    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);  
    }  
    /*开始监听*/  
    if (listen(httpd, 5) < 0)  
        error_die("listen");  
    /*返回 socket id */  
    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];  
  
    /* HTTP method 不被支持*/  
    sprintf(buf, "HTTP/1.0 501 Method Not Implemented\r\n");  
    send(client, buf, strlen(buf), 0);  
    /*服务器信息*/  
    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;  
    int client_sock = -1;  
    struct sockaddr_in client_name;  
    int client_name_len = sizeof(client_name);  
    pthread_t newthread;  
  
    /*在对应端口建立 httpd 服务*/  
    server_sock = startup(&port);  
    printf("httpd running on port %d\n", port);  
  
    while (1)  
    {  
        /*套接字收到客户端连接请求*/  
        client_sock = accept(server_sock,(struct sockaddr *)&client_name,&client_name_len);  
        if (client_sock == -1)  
            error_die("accept");  
        /*派生新线程用 accept_request 函数处理新请求*/  
        /* accept_request(client_sock); */  
        if (pthread_create(&newthread , NULL, accept_request, client_sock) != 0)  
            perror("pthread_create");  
    }  
  
    close(server_sock);  
  
    return(0);  
}