unix网络编程笔记---19.名字与地址转换

一. gethostbyname
1. 获取主机名

在/usr/include/netdb.h中
struct hostent
{
  char *h_name;          //主机的规范名:参见下面的sina.com
  char **h_aliases;      //主机的别名,可能有很多个所以这儿是个list
  int h_addrtype;        //ip地址类型,AF_INET(IPv4),AF_INET6(IPv6)
  int h_length;          //ip地址长度: 为4
  char **h_addr_list;    //主机的ip地址:网络字节序存储的
};

例如地址为:202.102.75.147
网络字节序是:0xca 0x66 0x4b 0x93
2.源码

cong@msi:/work/test/tcpip/19echo$ cat name.c
#include "utils.h"

int main ( int argc, char *argv[] )
{
    char *ptr, **pptr;
    char str[INET_ADDRSTRLEN];
    struct hostent *hptr;
    while( --argc > 0)
    {
        ptr = *++argv;
        if( (hptr = gethostbyname(ptr)) == NULL)
        {
            dbmsg("gethostbyname error");
            continue;
        }
        dbmsg("official hostname: %s", hptr->h_name);
        for(pptr=hptr->h_aliases; *pptr!=NULL; pptr++)
            dbmsg("alias:%s", *pptr);
        switch( hptr->h_addrtype)
        {
            case AF_INET:
                pptr = hptr->h_addr_list;
                for(; *pptr!=NULL; pptr++)
                    dbmsg("address:%s", inet_ntop(hptr->h_addrtype,*pptr,str, sizeof(str)));
                break;
        }
    }
    return EXIT_SUCCESS;
}

utils.h

cong@msi:/work/test/tcpip/19echo$ cat utils.h
#ifndef UTILS_H__
#define UTILS_H__
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <time.h>
#include <string.h>
#include <errno.h>
#include <signal.h>
#include <netdb.h>

#define MAXLINE 1024

#define LISTENQ 10
#define dbmsg(fmt, args ...) printf("%s:%s[%d]: "fmt"\n", __FILE__,__FUNCTION__, __LINE__,##args)
#define  max(a,b) ((a) > (b) ? (a) : (b))

#endif

3.运行结果

cong@msi:/work/test/tcpip/19echo$ ./name www.baidu.com
name.c:main[16]: official hostname: www.a.shifen.com
name.c:main[18]: alias:www.baidu.com
name.c:main[24]: address:180.97.33.108
name.c:main[24]: address:180.97.33.107

cong@msi:/work/test/tcpip/19echo$ ./name www.sina.com
name.c:main[16]: official hostname: newsnj.sina.com.cn    //看到没，主机的规范名与输入的是不一样的
name.c:main[18]: alias:www.sina.com
name.c:main[18]: alias:us.sina.com.cn
name.c:main[18]: alias:news.sina.com.cn
name.c:main[18]: alias:jupiter.sina.com.cn
name.c:main[24]: address:202.102.75.147

hostname.rar (下载后改名为hostname.tar.gz)

---

二. gethostbyaddr
2.1 查看gethostbyaddr的man_page 

a.原型:
#include <sys/socket.h> /* for AF_INET */
struct hostent *gethostbyaddr(const void *addr, socklen_t len, int type);
b.参数说明
type: The gethostbyaddr() valid address types are AF_INET and AF_INET6.
addr: The host address argument is a pointer to a struct of a type depending on the address type, for example a struct in_addr * (probably     obtained via a call to inet_addr(3)) for address type AF_INET. (addr参数可以通过net_addr()来得到)

2.2 代码

cong@msi:/work/test/tcpip/ch11/hostaddr$ cat addr.c
#include "utils.h"

int main ( int argc, char *argv[] )
{
    struct hostent *hptr;
    long    addr;
    if (argc != 2) {
        fprintf(stderr, "usage: %s i.p.addres", argv[0]);
        exit(1);
    }
    addr = inet_addr(argv[1]);
    hptr = gethostbyaddr((char *) &addr, sizeof(addr), AF_INET);
    if(NULL == hptr)
    {
        dbmsg("host %s not found", argv[1]);
        exit(1);
    }
    dbmsg("Hostname:%s", hptr->h_name);
    while (hptr->h_aliases[0])
        dbmsg("Aliases:%s", *hptr->h_aliases++);
    while (hptr->h_addr_list[0])
        dbmsg("Addresses:%s", inet_ntoa(*(struct in_addr *) * hptr->h_addr_list++));
    return EXIT_SUCCESS;
}

2.3 运行结果

cong@msi:/work/test/tcpip/ch11/hostaddr$ ./addr 8.8.8.8
addr.c:main[19]: Hostname:google-public-dns-a.google.com
addr.c:main[23]: Addresses:8.8.8.8

hostaddr.rar (下载后改名为hostaddr.tar.gz)

---

三. gethostbyname
3.1 获取主机的服务

#include
struct servent
{
  char *s_name;            //表示服务的名称
  char **s_aliases;        //服务的别名链表
  int s_port;              //端口号
  char *s_proto;           //服务的协议
};

也可在以/etc/services中查看
3.2 代码

cong@msi:/work/test/tcpip/ch11/servname$ cat servname.c
#include "utils.h"

int main ( int argc, char *argv[] )
{
    struct servent * sptr;
    if (argc != 3) {
        fprintf(stderr, "usage: %s i.p.addres", argv[0]);
        exit(1);
    }
    sptr = getservbyname(argv[1], argv[2]);
    if(NULL == sptr)
    {
        dbmsg("%s:%s not found",argv[1], argv[2]);
        exit(0);
    }
    dbmsg("name=%s, port=%d, protocal=%s",
            sptr->s_name, ntohs(sptr->s_port), sptr->s_proto);

    return EXIT_SUCCESS;
}

3.2 运行结果

cong@msi:/work/test/tcpip/ch11/servname$ ./servname domain udp
servname.c:main[17]: name=domain, port=53, protocal=udp
cong@msi:/work/test/tcpip/ch11/servname$ ./servname ftp tcp
servname.c:main[17]: name=ftp, port=21, protocal=tcp
cong@msi:/work/test/tcpip/ch11/servname$ ./servname ftp udp
servname.c:main[13]: ftp:udp not found

servname.rar (下载后改名为servname.tar.gz)

---

四. getservbyport
4.1 代码

cong@msi:/work/test/tcpip/ch11/servport$ cat servport.c
#include "utils.h"

int main ( int argc, char *argv[] )
{
    struct servent * sptr;
    int port;
    if (argc != 3) {
        fprintf(stderr, "usage: %s i.p.addres", argv[0]);
        exit(1);
    }
    port = atoi(argv[1]);                          //第1个参数是int型
    sptr = getservbyport(htons(port), argv[2]);    //并一定要转为网络字节序
    if(NULL == sptr)
    {
        dbmsg("%s:%s not found",argv[1], argv[2]);
        exit(0);
    }
    dbmsg("name=%s, port=%d, protocal=%s",
            sptr->s_name, ntohs(sptr->s_port), sptr->s_proto);

    return EXIT_SUCCESS;
}

4.2 运行结果

cong@msi:/work/test/tcpip/ch11/servport$ ./servport 53 udp
servport.c:main[19]: name=domain, port=53, protocal=udp
cong@msi:/work/test/tcpip/ch11/servport$ ./servport 21 tcp
servport.c:main[19]: name=ftp, port=21, protocal=tcp
cong@msi:/work/test/tcpip/ch11/servport$ ./servport 21 udp
servport.c:main[19]: name=fsp, port=21, protocal=udp

servport.rar (下载后改名为servport.tar.gz)    

---

五. getaddrinfo

int getaddrinfo(const char *node, const char *service,
                       const struct addrinfo *hints,
                       struct addrinfo **res);