/* 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>
#include <stdint.h>

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

#define SERVER_STRING "Server: jdbhttpd/0.1.0\r\n"
#define STDIN   0
#define STDOUT  1
#define STDERR  2

void accept_request(void *);//接受请求
void bad_request(int);//http 400错误-请求无效
void cat(int, FILE *);//读文件
void cannot_execute(int);//http 500错误-内部服务器错误
void error_die(const char *);//输出报错信息
void execute_cgi(int, const char *, const char *, const char *);//执行cgi
int get_line(int, char *, int);//读取一行
void headers(int, const char *);//http 200-请求成功
void not_found(int);//http 404错误-请求的网页不存在
void serve_file(int, const char *);//不是cgi，直接读文件返回
int startup(u_short *);//开tcp
void unimplemented(int);//http 501错误-未实现

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


//GET / HTTP/1.1
//Host: 127.0.0.1:4000
//Cache-Control: max-age=0
//Upgrade-Insecure-Requests: 1
//User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.70 Safari/537.36
//Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
//Accept-Encoding: gzip, deflate
//Accept-Language: zh-CN,zh;q=0.9
//Cookie: session=dd3ca7df-0729-436d-864b-d1f1851b2d97
//Connection: close



//POST /color.cgi HTTP/1.1
//Host: 127.0.0.1:4000
//Content-Length: 9
//Cache-Control: max-age=0
//Origin: http://127.0.0.1:4000
//Upgrade-Insecure-Requests: 1
//Content-Type: application/x-www-form-urlencoded
//User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.70 Safari/537.36
//Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3
//Referer: http://127.0.0.1:4000/
//Accept-Encoding: gzip, deflate
//Accept-Language: zh-CN,zh;q=0.9
//Cookie: session=dd3ca7df-0729-436d-864b-d1f1851b2d97
//Connection: close

//color=red

void accept_request(void *arg)
{
    int client = (intptr_t)arg;
    char buf[1024];
    size_t 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;

    numchars = get_line(client, buf, sizeof(buf));//读http请求头第一行，判断请求方法
    i = 0; j = 0;
    while (!ISspace(buf[i]) && (i < sizeof(method) - 1))//获取请求方法
    {
        method[i] = buf[i];
        i++;
    }
    j=i;
    method[i] = '\0';

    if (strcasecmp(method, "GET") && strcasecmp(method, "POST"))//判断是GET还是POST，如果都不是就报501
    {
        unimplemented(client);
        return;
    }

    if (strcasecmp(method, "POST") == 0)//POST方法
        cgi = 1;

    i = 0;
    while (ISspace(buf[j]) && (j < numchars))//跳过空格
        j++;
    while (!ISspace(buf[j]) && (i < sizeof(url) - 1) && (j < numchars))//获取url
    {
        url[i] = buf[j];
        i++; j++;
    }
    url[i] = '\0';

    if (strcasecmp(method, "GET") == 0)//GET方法
    {
        query_string = url;
        while ((*query_string != '?') && (*query_string != '\0'))
            query_string++;
        if (*query_string == '?')
        {
            cgi = 1;
            *query_string = '\0';
            query_string++;
        }
    }

    sprintf(path, "htdocs%s", url);//路径
    if (path[strlen(path) - 1] == '/')//如果路径是/，加上index.html
        strcat(path, "index.html");
    if (stat(path, &st) == -1) {//获取文件信息，成功返回0，失败返回-1
        while ((numchars > 0) && 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)//判断st是否是一个目录
            strcat(path, "/index.html");
        if ((st.st_mode & S_IXUSR) ||
                (st.st_mode & S_IXGRP) ||
                (st.st_mode & S_IXOTH)    )//如果有可执行权限，判断为cgi，cgi置为1
            cgi = 1;
        if (!cgi)//如果不是cgi，读取后返回，是cgi就执行
            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];

    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];

    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];

    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);
    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];//output管道
    int cgi_input[2];//input管道
    pid_t pid;//进程pid
    int status;//进程状态
    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index.html，http头后面的信息没必要分析*/
        while ((numchars > 0) && strcmp("\n", buf))  /* read & discard headers */
            numchars = get_line(client, buf, sizeof(buf));
    else if (strcasecmp(method, "POST") == 0) /*POST*/
    {
        numchars = get_line(client, buf, sizeof(buf));
        while ((numchars > 0) && strcmp("\n", buf))//读取Content-Length
        {
            buf[15] = '\0';
            if (strcasecmp(buf, "Content-Length:") == 0)
                content_length = atoi(&(buf[16]));//从buf[16]开始的字符串转化为int
            numchars = get_line(client, buf, sizeof(buf));
        }
        if (content_length == -1) {
            bad_request(client);
            return;
        }
    }
    else/*HEAD or other*/
    {
    }


    if (pipe(cgi_output) < 0) {//创建管道失败
        cannot_execute(client);
        return;
    }
    if (pipe(cgi_input) < 0) {//创建管道失败
        cannot_execute(client);
        return;
    }

    if ( (pid = fork()) < 0 ) {//fork进程失败
        cannot_execute(client);
        return;
    }
    //子进程执行cgi，父进程接收、发送数据
    sprintf(buf, "HTTP/1.0 200 OK\r\n");
    send(client, buf, strlen(buf), 0);
    if (pid == 0)  /* child: CGI script */
    {
        char meth_env[255];
        char query_env[255];
        char length_env[255];

        dup2(cgi_output[1], STDOUT);//子进程输出重定向到output管道的1端
        dup2(cgi_input[0], STDIN);//子进程输入重定向到input管道的0端
        close(cgi_output[0]);//关闭无用管道口
        close(cgi_input[1]);//关闭无用管道口
        sprintf(meth_env, "REQUEST_METHOD=%s", method);
        putenv(meth_env);//CGI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);
        }
        execl(path, NULL);//执行
        exit(0);
    } else {    /* parent */
        close(cgi_output[1]);//关闭无用管道口
        close(cgi_input[0]);//关闭无用管道口
        if (strcasecmp(method, "POST") == 0)//POST方法
            for (i = 0; i < content_length; i++) {
                recv(client, &c, 1, 0);
                write(cgi_input[1], &c, 1);//把post请求数据写到input管道中，供子进程使用
            }
        while (read(cgi_output[0], &c, 1) > 0)
            send(client, &c, 1, 0);//从output管道读取子进程处理后的数据，然后发送

        close(cgi_output[0]);//关闭管道口
        close(cgi_input[1]);//关闭管道口
        waitpid(pid, &status, 0);//暂时停止目前进程的执行，直到有信号来到或子进程结束
    }
}

/**********************************************************************/
/* 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'))
    {
        n = recv(sock, &c, 1, 0);//recv返回成功读取的字节数
        /* DEBUG printf("%02X\n", c); */
        if (n > 0)
        {
            if (c == '\r')//如果是\r，用MSG_PEEK再读取一个字符。把tcp buffer中的数据读取到buf中，并不把已读取的数据从tcp buffer中移除，再次调用recv仍然可以读到刚才读到的数据
            {
                n = recv(sock, &c, 1, MSG_PEEK);
                /* DEBUG printf("%02X\n", c); */
                if ((n > 0) && (c == '\n'))//如果是\n，再读一个，根据MSG_PEEK，还是\n
                    recv(sock, &c, 1, 0);
                else
                    c = '\n';//如果不是\n则置为\n
            }
            buf[i] = c;
            i++;
        }
        else
            c = '\n';
    }
    buf[i] = '\0';//以NULL结束

    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 */

    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];

    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';
    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);
    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 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;
    int on = 1;
    struct sockaddr_in name;

    httpd = socket(PF_INET, SOCK_STREAM, 0);//创建socket descriptor
    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 ((setsockopt(httpd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on))) < 0)  
    {  
        error_die("setsockopt failed");
    }
    if (bind(httpd, (struct sockaddr *)&name, sizeof(name)) < 0)//把一个地址族中的特定地址赋给socke，成功返回0，错误返回-1
        error_die("bind");
    if (*port == 0)  /* if dynamically allocating a port */
    {
        socklen_t namelen = sizeof(name);
        if (getsockname(httpd, (struct sockaddr *)&name, &namelen) == -1)//获取一个套接字的名字，成功返回0，错误返回-1
            error_die("getsockname");
        *port = ntohs(name.sin_port);//将一个16位数由网络字节顺序转换为主机字节顺序
    }
    if (listen(httpd, 5) < 0)//监听socket，成功返回0，错误返回-1
        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[1024];

    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 = 4000;
    int client_sock = -1;
    struct sockaddr_in client_name;
    socklen_t  client_name_len = sizeof(client_name);
    pthread_t newthread;

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

    while (1)
    {
        client_sock = accept(server_sock,
                (struct sockaddr *)&client_name,
                &client_name_len);//接收请求，失败返回-1
        if (client_sock == -1)
            error_die("accept");
        /* accept_request(&client_sock); */
        if (pthread_create(&newthread , NULL, (void *)accept_request, (void *)(intptr_t)client_sock) != 0)//创建线程处理请求，成功返回0
            perror("pthread_create");
    }

    close(server_sock);//把套接字标记为已关闭

    return(0);
}