深入理解计算机系统 第11章 习题解析

这次回顾第11章习题。

电子书地址：

http://eol.bnuz.edu.cn/meol/common/script/preview/download_preview.jsp?fileid=2169600&resid=242120&lid=28605

参考资料：

https://dreamanddead.github.io/CSAPP-3e-Solutions/chapter11/

https://www.cnblogs.com/wei-hj/p/7859707.html

https://www.cnblogs.com/pu369/p/12201707.html

https://chrome.google.com/webstore/detail/postman/fhbjgbiflinjbdggehcddcbncdddomop/related

https://blog.csdn.net/chenchunlin526/article/details/78981965

代码均修改自

Code-all/code/netp/tiny/tiny.c

11.6

A

int main(int argc, char **argv) 
{
    int listenfd, connfd;
    char hostname[MAXLINE], port[MAXLINE];
    socklen_t clientlen;
    struct sockaddr_storage clientaddr;

    /* Check command line args */
    if (argc != 2) {
	fprintf(stderr, "usage: %s <port>\n", argv[0]);
	exit(1);
    }

    listenfd = Open_listenfd(argv[1]);
    while (1) {
        clientlen = sizeof(clientaddr);
        connfd = Accept(listenfd, (SA *)&clientaddr, &clientlen); //line:netp:tiny:accept
        Getnameinfo((SA *) &clientaddr, clientlen, hostname, MAXLINE, port, MAXLINE, 0);
        printf("Accepted connection from (%s, %s)\n", hostname, port);
        // doit(connfd);                                             //line:netp:tiny:doit
        print_raw(connfd);
        Close(connfd);                                            //line:netp:tiny:close
    }
}
/* $end tinymain */

// add
void print_raw(int fd) {
    ssize_t n;
    char buf[MAXLINE];
    rio_t rio;
    Rio_readinitb(&rio, fd);
    while (Rio_readlineb(&rio, buf, MAXLINE)) {
        // 结束则退出
        if (strcmp(buf, "\r\n") == 0) {
            break;
        }
        printf("%s\n", buf);
    }
}

B

运行并测试：

make
./tiny 8888

结果：

Accepted connection from (localhost, 57586)
GET /home.html HTTP/1.1

Host: localhost:8888

Connection: keep-alive

sec-ch-ua: "Google Chrome";v="93", " Not;A Brand";v="99", "Chromium";v="93"

sec-ch-ua-mobile: ?0

sec-ch-ua-platform: "Windows"

Upgrade-Insecure-Requests: 1

User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/93.0.4577.82 Safari/537.36

Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.9

Sec-Fetch-Site: none

Sec-Fetch-Mode: navigate

Sec-Fetch-User: ?1

Sec-Fetch-Dest: document

Accept-Encoding: gzip, deflate, br

Accept-Language: zh-CN,zh;q=0.9

C

HTTP/1.1

11.7

修改代码：

/*
 * get_filetype - derive file type from file name
 */
void get_filetype(char *filename, char *filetype) 
{
    if (strstr(filename, ".html"))
	strcpy(filetype, "text/html");
    else if (strstr(filename, ".gif"))
	strcpy(filetype, "image/gif");
    else if (strstr(filename, ".png"))
	strcpy(filetype, "image/png");
    else if (strstr(filename, ".jpg"))
	strcpy(filetype, "image/jpeg");
    // add
    else if (strstr(filename, ".mpeg"))
    strcpy(filetype, "video/mpeg");
    else
	strcpy(filetype, "text/plain");
}

11.8

修改代码：

void handler(int sig) {
    printf("CGI stop\n");
}

void serve_dynamic(int fd, char *filename, char *cgiargs) 
{
    char buf[MAXLINE], *emptylist[] = { NULL };

    /* Return first part of HTTP response */
    sprintf(buf, "HTTP/1.0 200 OK\r\n"); 
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Server: Tiny Web Server\r\n");
    Rio_writen(fd, buf, strlen(buf));

    // add
    Signal(SIGCHLD, handler);
  
    if (Fork() == 0) { /* Child */ //line:netp:servedynamic:fork
	/* Real server would set all CGI vars here */
	setenv("QUERY_STRING", cgiargs, 1); //line:netp:servedynamic:setenv
	Dup2(fd, STDOUT_FILENO);         /* Redirect stdout to client */ //line:netp:servedynamic:dup2
	Execve(filename, emptylist, environ); /* Run CGI program */ //line:netp:servedynamic:execve
    }
    // Wait(NULL); /* Parent waits for and reaps child */ //line:netp:servedynamic:wait
}

11.9

void serve_static(int fd, char *filename, int filesize)
{
    int srcfd;
    char *srcp, filetype[MAXLINE], buf[MAXBUF];

    /* Send response headers to client */
    get_filetype(filename, filetype);    //line:netp:servestatic:getfiletype
    sprintf(buf, "HTTP/1.0 200 OK\r\n"); //line:netp:servestatic:beginserve
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Server: Tiny Web Server\r\n");
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Content-length: %d\r\n", filesize);
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Content-type: %s\r\n\r\n", filetype);
    Rio_writen(fd, buf, strlen(buf));    //line:netp:servestatic:endserve

    /* Send response body to client */
    // add
    srcfd = Open(filename, O_RDONLY, 0);
    void* ptr = malloc(filesize);
    // 将srcfd指定的磁盘文件映射到ptr
    Rio_readn(srcfd, ptr, filesize);
    Rio_writen(fd, ptr, filesize);
    free(ptr);
}

11.10

get方法示例：

https://www.w3school.com.cn/tags/att_form_method.asp

https://developer.mozilla.org/zh-CN/docs/Web/HTML/Element/Input

A

新增文件adder.html：

<form action="./cgi-bin/adder?" method="get">
       <p>number1: <input type="text" name="number1" /></p>
       <p>number2: <input type="text" name="number2" /></p>
       <input type="submit" value="Submit" />
</form>

修改文件cgi-bin/adder.c：

/*
 * adder.c - a minimal CGI program that adds two numbers together
 */
/* $begin adder */
#include "csapp.h"

int main(void) {
    char *buf, *p;
    char arg1[MAXLINE], arg2[MAXLINE], content[MAXLINE];
    int n1=0, n2=0;

    /* Extract the two arguments */
    if ((buf = getenv("QUERY_STRING")) != NULL) {
        p = strchr(buf, '&');
        *p = '\0';
        strcpy(arg1, buf);
        strcpy(arg2, p+1);
        sscanf(arg1, "number1=%d", &n1);
        sscanf(arg2, "number2=%d", &n2);
    }

    /* Make the response body */
    sprintf(content, "Welcome to add.com: ");
    sprintf(content, "%sTHE Internet addition portal.\r\n<p>", content);

    sprintf(content, "%sThe answer is: %d + %d = %d\r\n<p>", 
	    content, n1, n2, n1 + n2);
    sprintf(content, "%sThanks for visiting!\r\n", content);
    /* Generate the HTTP response */
    printf("Connection: close\r\n");
    printf("Content-length: %d\r\n", (int)strlen(content));
    printf("Content-type: text/html\r\n\r\n");
    printf("%s", content);
    fflush(stdout);

    exit(0);
}
/* $end adder */

B

测试：

编译运行：

make
./tiny 8888

访问url：

http://localhost:8888/adder.html

得到界面：

输入并提交：

跳转到url：

http://localhost:8888/cgi-bin/adder?number1=123&number2=456

运行结果为：

11.11

修改代码：

void doit(int fd) 
{
    int is_static;
    struct stat sbuf;
    char buf[MAXLINE], method[MAXLINE], uri[MAXLINE], version[MAXLINE];
    char filename[MAXLINE], cgiargs[MAXLINE];
    rio_t rio;

    /* Read request line and headers */
    Rio_readinitb(&rio, fd);
    if (!Rio_readlineb(&rio, buf, MAXLINE))  //line:netp:doit:readrequest
        return;
    printf("%s", buf);
    sscanf(buf, "%s %s %s", method, uri, version);       //line:netp:doit:parserequest

    // add
    int flag;
    if (!strcasecmp(method, "GET")) {                     //line:netp:doit:beginrequesterr
        flag = 0;
    }else if (!strcasecmp(method, "HEAD")) {
        flag = 1;
    }else {
        clienterror(fd, method, "501", "Not Implemented",
                    "Tiny does not implement this method");
        return;
    }                                                  //line:netp:doit:endrequesterr
    read_requesthdrs(&rio);                              //line:netp:doit:readrequesthdrs

    /* Parse URI from GET request */
    is_static = parse_uri(uri, filename, cgiargs);       //line:netp:doit:staticcheck
    if (stat(filename, &sbuf) < 0) {                     //line:netp:doit:beginnotfound
	clienterror(fd, filename, "404", "Not found",
		    "Tiny couldn't find this file");
	return;
    }                                                    //line:netp:doit:endnotfound

    if (is_static) { /* Serve static content */          
	if (!(S_ISREG(sbuf.st_mode)) || !(S_IRUSR & sbuf.st_mode)) { //line:netp:doit:readable
	    clienterror(fd, filename, "403", "Forbidden",
			"Tiny couldn't read the file");
	    return;
	}
    // change
	serve_static(fd, filename, sbuf.st_size, flag);        //line:netp:doit:servestatic
    }
    else { /* Serve dynamic content */
	if (!(S_ISREG(sbuf.st_mode)) || !(S_IXUSR & sbuf.st_mode)) { //line:netp:doit:executable
	    clienterror(fd, filename, "403", "Forbidden",
			"Tiny couldn't run the CGI program");
	    return;
	}
    // change
	serve_dynamic(fd, filename, cgiargs, flag);            //line:netp:doit:servedynamic
    }
}

void serve_static(int fd, char *filename, int filesize, int flag)
{
    int srcfd;
    char *srcp, filetype[MAXLINE], buf[MAXBUF];

    /* Send response headers to client */
    get_filetype(filename, filetype);    //line:netp:servestatic:getfiletype
    sprintf(buf, "HTTP/1.0 200 OK\r\n"); //line:netp:servestatic:beginserve
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Server: Tiny Web Server\r\n");
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Content-length: %d\r\n", filesize);
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Content-type: %s\r\n\r\n", filetype);
    Rio_writen(fd, buf, strlen(buf));    //line:netp:servestatic:endserve

    if (flag) {
        return;
    }

    /* Send response body to client */
    srcfd = Open(filename, O_RDONLY, 0); //line:netp:servestatic:open
    srcp = Mmap(0, filesize, PROT_READ, MAP_PRIVATE, srcfd, 0); //line:netp:servestatic:mmap
    Close(srcfd);                       //line:netp:servestatic:close
    Rio_writen(fd, srcp, filesize);     //line:netp:servestatic:write
    Munmap(srcp, filesize);             //line:netp:servestatic:munmap
}

void serve_dynamic(int fd, char *filename, char *cgiargs, int flag) 
{
    char buf[MAXLINE], *emptylist[] = { NULL };

    /* Return first part of HTTP response */
    sprintf(buf, "HTTP/1.0 200 OK\r\n"); 
    Rio_writen(fd, buf, strlen(buf));
    sprintf(buf, "Server: Tiny Web Server\r\n");
    Rio_writen(fd, buf, strlen(buf));

    if (flag) {
        return;
    }
  
    if (Fork() == 0) { /* Child */ //line:netp:servedynamic:fork
	/* Real server would set all CGI vars here */
	setenv("QUERY_STRING", cgiargs, 1); //line:netp:servedynamic:setenv
	Dup2(fd, STDOUT_FILENO);         /* Redirect stdout to client */ //line:netp:servedynamic:dup2
	Execve(filename, emptylist, environ); /* Run CGI program */ //line:netp:servedynamic:execve
    }
    Wait(NULL); /* Parent waits for and reaps child */ //line:netp:servedynamic:wait
}

测试：

修改前：

telnet localhost 8888
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET /home.html HTTP/1.1

HTTP/1.0 200 OK
Server: Tiny Web Server
Content-length: 120
Content-type: text/html

<html>
<head><title>test</title></head>
<body> 
<img align="middle" src="godzilla.gif">
Dave O'Hallaron
</body>
</html>
Connection closed by foreign host.

修改后：

telnet localhost 8888
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
HEAD /home.html HTTP/1.1

HTTP/1.0 200 OK
Server: Tiny Web Server
Content-length: 120
Content-type: text/html

Connection closed by foreign host.

11.12

参考资料：

https://www.cnblogs.com/pu369/p/12201707.html

https://chrome.google.com/webstore/detail/postman/fhbjgbiflinjbdggehcddcbncdddomop/related

https://blog.csdn.net/chenchunlin526/article/details/78981965

修改代码：

void doit(int fd) 
{
    int is_static;
    struct stat sbuf;
    char buf[MAXLINE], method[MAXLINE], uri[MAXLINE], version[MAXLINE];
    char filename[MAXLINE], cgiargs[MAXLINE];
    rio_t rio;

    /* Read request line and headers */
    Rio_readinitb(&rio, fd);
    if (!Rio_readlineb(&rio, buf, MAXLINE))  //line:netp:doit:readrequest
        return;
    printf("%s", buf);
    sscanf(buf, "%s %s %s", method, uri, version);       //line:netp:doit:parserequest
    
    if (strcasecmp(method, "GET") && strcasecmp(method, "POST")) {                     //line:netp:doit:beginrequesterr
        
        clienterror(fd, method, "501", "Not Implemented",
                    "Tiny does not implement this method");
        return;
    }

    // add
    // 获得body长度
    int len = read_requesthdrs(&rio);
    if (strncasecmp(method, "POST", 4) == 0) {
        Rio_readnb(&rio, buf, len);
        serve_dynamic(fd, filename, buf);
        
        return;
    }
    /* Parse URI from GET request */
    is_static = parse_uri(uri, filename, cgiargs);       //line:netp:doit:staticcheck
    if (stat(filename, &sbuf) < 0) {                     //line:netp:doit:beginnotfound
	clienterror(fd, filename, "404", "Not found",
		    "Tiny couldn't find this file");
	return;
    }                                                    //line:netp:doit:endnotfound

    if (is_static) { /* Serve static content */          
	if (!(S_ISREG(sbuf.st_mode)) || !(S_IRUSR & sbuf.st_mode)) { //line:netp:doit:readable
	    clienterror(fd, filename, "403", "Forbidden",
			"Tiny couldn't read the file");
	    return;
	}
	serve_static(fd, filename, sbuf.st_size);        //line:netp:doit:servestatic
    }
    else { /* Serve dynamic content */
	if (!(S_ISREG(sbuf.st_mode)) || !(S_IXUSR & sbuf.st_mode)) { //line:netp:doit:executable
	    clienterror(fd, filename, "403", "Forbidden",
			"Tiny couldn't run the CGI program");
	    return;
	}
	serve_dynamic(fd, filename, cgiargs);            //line:netp:doit:servedynamic
    }
}

// change
int read_requesthdrs(rio_t *rp) 
{
    char buf[MAXLINE];
    int len;

    Rio_readlineb(rp, buf, MAXLINE);
    printf("%s", buf);
    while(strcmp(buf, "\r\n")) {          //line:netp:readhdrs:checkterm
        Rio_readlineb(rp, buf, MAXLINE);
        printf("%s", buf);
        // 获得body长度
        if (strncasecmp(buf, "Content-Length:", 15) == 0) {
            sscanf(buf, "Content-Length: %d", &len);
        }
    }

    return len;
}

利用postman测试：

11.13

修改代码：

// add
void handler(int sig)
{
    if (errno == EPIPE) {
        fprintf(stderr, "Broken pipe\n");
    }
    exit(1);
}

int main(int argc, char **argv) 
{
    // add
    Signal(SIGPIPE, handler);
    int listenfd, connfd;
    char hostname[MAXLINE], port[MAXLINE];
    socklen_t clientlen;
    struct sockaddr_storage clientaddr;

    /* Check command line args */
    if (argc != 2) {
	fprintf(stderr, "usage: %s <port>\n", argv[0]);
	exit(1);
    }

    listenfd = Open_listenfd(argv[1]);
    while (1) {
	clientlen = sizeof(clientaddr);
	connfd = Accept(listenfd, (SA *)&clientaddr, &clientlen); //line:netp:tiny:accept
        Getnameinfo((SA *) &clientaddr, clientlen, hostname, MAXLINE, 
                    port, MAXLINE, 0);
        printf("Accepted connection from (%s, %s)\n", hostname, port);
	doit(connfd);                                             //line:netp:tiny:doit
	Close(connfd);                                            //line:netp:tiny:close
    }
}