tinyhttp源码阅读(注释)

这里就不细述了,代码很简单.
其实现的功能比较若,可以做一个参考.
因为其通过文件的权限位来判断是否是一个CGI脚本,所以在权限位不对的情况下会判断不正确.例如我将这个目录放置在NTFS分区,所有的文件都有可执行权限,会导致将index.html文件当做CGI脚本.

注释后的文件在这里下载http://files.cnblogs.com/files/oloroso/tinyhttpd-0.1.0.tar.7z

/* 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/0.1.0rn"

// 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'rn'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] = '';
    // 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] = '';

    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 != '')){
            query_string++;
        }
        if (*query_string == '?')
        {
            cgi = 1;
            *query_string = '';   // 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 REQUESTrn");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "Content-type: text/htmlrn");
    send(client, buf, sizeof(buf), 0);
    sprintf(buf, "rn");
    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.rn");
    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 Errorrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-type: text/htmlrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<P>Error prohibited CGI execution.rn");
    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] = '';

    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] = '';
            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 OKrn");
    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 = '';
    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("%02Xn", c); */
        if (n > 0)
        {
            // 将 rn 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("%02Xn", 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] = '';
    // 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 OKrn");
    send(client, buf, strlen(buf), 0);
    strcpy(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/htmlrn");
    send(client, buf, strlen(buf), 0);
    strcpy(buf, "rn");
    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 FOUNDrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/htmlrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<HTML><TITLE>Not Found</TITLE>rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>The server could not fulfillrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "your request because the resource specifiedrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "is unavailable or nonexistent.rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>rn");
    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] = '';
    // 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 Implementedrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, SERVER_STRING);
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "Content-Type: text/htmlrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<HTML><HEAD><TITLE>Method Not Implementedrn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</TITLE></HEAD>rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "<BODY><P>HTTP request method not supported.rn");
    send(client, buf, strlen(buf), 0);
    sprintf(buf, "</BODY></HTML>rn");
    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 %dn", 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);
}