APUE16章的运行示例16-14

参考文章：http://blog.csdn.net/andyxie407/article/details/1672325

今天在运行在APUE第16章的16-14(客户端)和16-15(服务端)遇到了不少问题，搞了半天，运行方法多谢andyxie407的文章给了很好地参考(本来就一样，不叫参考)，后面还是运行不出结果，结果找到了两个程序抄错了的地方(原谅我，有时候，看一眼大概实现就把代码敲上去了)，写都写到这了，还是把我的痛苦运行结果展示一番，代码如下：

//16-14.c 即客户端
#include "apue.h"
#include <netdb.h>
#include <errno.h>
#include <sys/socket.h>

#define MAXADDRLEN 256
#define BUFLEN 128

#define MAXSLLEP 128
int connect_retry(int sockfd, struct sockaddr *addr, socklen_t alen)
{
    int nsec;

    for ( nsec = 1; nsec < MAXSLLEP; nsec <<= 1) {//nsec <<= 1 equal to nsec = nsec << 1 equal to nsec /= 2;
        if (connect(sockfd, addr, alen) == 0)
            return 0;
        if (nsec <= MAXSLLEP/2)
            sleep(nsec);
    }
    return -1;
}

void print_uptime(int sockfd)
{
    char    buf[BUFLEN];
    int     n;

    while ((n = recv(sockfd, buf, BUFLEN, 0)) > 0)
        write(STDOUT_FILENO, buf, n);
    if (n < 0)
        err_sys("recv error");
}

int main(int argc, char *argv[])
{
    struct addrinfo *aip, *ailist;
    struct addrinfo hint;
    int     err, sockfd;

    if (argc != 2)
        err_quit("Usage: ruptime hostname");
    hint.ai_family      = 0;
    hint.ai_flags       = 0;//AI_CANONNAME;
    hint.ai_socktype    = SOCK_STREAM;
    hint.ai_protocol    = 0;
    hint.ai_addrlen     = 0;
    hint.ai_canonname   = NULL;
    hint.ai_addr        = NULL;
    hint.ai_next        = NULL;

    if ((err = getaddrinfo(argv[1], "ruptime", &hint, &ailist)) != 0)
        err_quit("getaddrinfo:%s", gai_strerror(err));
    for (aip = ailist; aip != NULL; aip = aip->ai_next) {
        if ((sockfd = socket(aip->ai_family, SOCK_STREAM, 0)) < 0) {
            err = errno;
        }
        if (connect_retry(sockfd, aip->ai_addr, aip->ai_addrlen) < 0)
            err = errno;
        else {
            printf("connect to ruptime server successfully !
");
            print_uptime(sockfd);
            exit(0);
        }
    }
    fprintf(stderr, "cannot connect to %s:%s
", argv[1], strerror(err));
    exit(1); //err happened
}

//16-15.c即服务端
#include "apue.h"
#include <netdb.h>
#include <syslog.h>
#include <errno.h>
#include <sys/socket.h>

#define BUFLEN  128
#define QLEN    10

#ifndef HOST_NAME_MAX
#define HOST_NAME_MAX 256
#endif

int init_server(int type, struct sockaddr *addr, socklen_t alen, int qlen)
{
    int fd, err = 0;

    if ((fd = socket(addr->sa_family, type, 0)) < 0)
        return -1;
    if (bind(fd, addr, alen) < 0) {
        err = errno;
        goto errout;
    }
    if (type == SOCK_STREAM || type == SOCK_SEQPACKET) {
        if (listen(fd, QLEN) < 0) {
            err = errno;
            goto errout;
        }
    }
    return fd;      //successful when prog arrive here.

errout:
    close(fd);      //exit with failuare
    errno = err;
    return -1;
}

void serve(int fd)
{
    char    buf[BUFLEN];
    int     clfd;
    FILE    *fp;

    for ( ; ; ) {
        if ((clfd = accept(fd, NULL, NULL)) < 0) {
            syslog(LOG_ERR, "ruptime: accept error:%s", strerror(errno));
            exit(1);
        }
        if ((fp = popen("/usr/bin/uptime", "r")) == NULL) {
            sprintf(buf, "error:%s
", strerror(errno));
            send(clfd, buf, strlen(buf), 0);
        } else {
            while (fgets(buf, BUFLEN, fp) != NULL)
                send(clfd, buf, strlen(buf), 0);
            pclose(fp);
        }
        close(clfd); //send end
    }
}

int main(int argc, char *argv[])
{
    struct addrinfo *ailist, *aip;
    struct addrinfo hint;
    int     err, sockfd, n;
    char    *host;

    if (argc != 1)
        err_quit("Usage:service");

#ifdef _SC_HOST_NAME_MAX
    n = sysconf(_SC_HOST_NAME_MAX);
    if (n < 0)
#endif
        n = HOST_NAME_MAX;
    host = malloc(n);
    if (!host)
        err_sys("malloc error");
    if (gethostname(host, n) < 0)
        err_sys("gethostname");
    printf("host name is:%s
", host);
    daemonize("ruptimed");

    hint.ai_flags       = AI_CANONNAME;
    hint.ai_family      = 0;
    hint.ai_socktype    = SOCK_STREAM;
    hint.ai_protocol    = 0;
    hint.ai_addrlen     = 0;
    hint.ai_canonname   = NULL;
    hint.ai_addr        = NULL;
    hint.ai_next        = NULL;

    if ((err = getaddrinfo(host, "ruptime", &hint, &ailist)) != 0) {
        syslog(LOG_ERR , "ruptime:getaddrinfo error:%s", gai_strerror(err));
        exit(1);
    }

    for (aip = ailist; aip != NULL; aip = aip->ai_next) {
        sockfd = init_server(SOCK_STREAM, aip->ai_addr, aip->ai_addrlen, QLEN);
        if (sockfd >= 0){
            serve(sockfd);
            exit(0);
        }
    }
    exit(1);
}

分别编译成可执行文件，然后运行服务端 ./ruptimed，可以通过/var/log/syslog看到发生了错误

Servname not supported for ai_socktype .

解决方法之一：先到/etc/services中添加如下内容

ruptime 4000/tcp

保存离开，但是你要确保4000这个端口没有被其他服务占用，否则改用其他端口。这时先运行

$./ruptimed

这是16-15编译出的名字，可以通过ps -ef 看到刚才的程序已成为后台程序，再运行

$./ruptime ubuntu

前面那个是16-14编译出的名字，后面那个是用户/主机名(前面有篇文章讲到了，但是这里不能用localhost或127.0.0.1

得到结果。

12:06:45 up 21:40,  2 users,  load average: 0.00, 0.01, 0.05

很兴奋有木有！

还有一种方法不用更改/etc/services的方法，是将程序中的服务名改成端口号，然后改些其他内容，详见参考文章!

顺便提醒自己一句：在你不能保证自己程序的正确性时（即便编译通过不能代表没有写错或写漏一些东西），先不要到处找程序之外的任何原因，谨记！