getaddrinfo( ) - getnameinfo( )/ inet_ntop( )

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本文介绍了一个C语言程序，该程序使用getaddrinfo()函数解析主机名和服务端口，并通过addrinfo_ntop()函数将得到的地址信息转换为更易读的形式。程序还展示了如何使用getnameinfo()获取主机的反向DNS记录。

/*   addrinfo_ntop.c by vinco at 2012-05-18
 *   i386-Red Hat-gcc-4.1.2 
 *   http://blog.youkuaiyun.com/xuyunzhang/
 *   Copyright: All Reserved
 */

#include <stdio.h>
#include <string.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

int addrinfo(char* host, char *serv);
int addrinfo_ntop(const struct addrinfo *paddrinfo,
                       char *host, size_t hostlen,
                       char *serv, size_t servlen);
int main()
{
	char host[64]="member.qq.com", serv[64]="8000";
	//char host[64]="183.60.49.253", serv[64]="8000";
	addrinfo( host, serv);
}

int addrinfo(char* host, char *serv)
{
	struct addrinfo hints, *res = NULL, *paddrinfo = NULL;
	char hostname[64]={0}, servname[64]={0};
	int ret = -1;

	if( !host || !serv )
		return -1;
	memset(&hints, 0, sizeof(hints));
	hints.ai_family = AF_UNSPEC; /* AF_INET6 or AF_INET */
	hints.ai_socktype = SOCK_DGRAM;
	//hints.ai_flags = ;
	
	if( (ret = getaddrinfo( host, serv, &hints, &res)) )
	{
		printf("getaddrinfo error:%s\n", gai_strerror(ret) );
		return -1;
	}
		
	for(paddrinfo = res; paddrinfo; paddrinfo = paddrinfo->ai_next )
	{
		if( addrinfo_ntop(paddrinfo,
					hostname, sizeof(hostname),
					servname, sizeof(servname)) == 0 )
		{
			ret = 0;
			fprintf(stderr, "addrinfo_ntop host/port = %s/%s\t", hostname, servname);
		}
		
		if( getnameinfo(paddrinfo->ai_addr, paddrinfo->ai_addrlen, 
					hostname, sizeof(hostname), 
					servname, sizeof(servname), 
					/*NI_NUMERICHOST | NI_NUMERICSERV*/ 0) == 0 ) 
		{
			ret = 0;
			fprintf(stderr, "getnameinfo host/port = %s/%s\n", hostname, servname);
		}
	}

	putchar('\n');
	
	freeaddrinfo(res);
	return ret;
	
}

int addrinfo_ntop(const struct addrinfo *paddrinfo,
                       char *host, size_t hostlen,
                       char *serv, size_t servlen)
{
	struct sockaddr_in *sain = NULL;
	struct sockaddr_in6 *sain6 = NULL;

	if( !paddrinfo || !host || !serv )
		return -1;
	switch ( paddrinfo->ai_family) 
	{
		case AF_INET: 
		{
			sain = (struct sockaddr_in *)(paddrinfo->ai_addr);
			inet_ntop( paddrinfo->ai_family, &(sain->sin_addr), host, hostlen);
			snprintf( serv, servlen, "%d", ntohs(sain->sin_port) );
			return 0;
		}
		break;

		case AF_INET6: 
		{
			sain6 = (struct sockaddr_in6 *)(paddrinfo->ai_addr);
			inet_ntop( paddrinfo->ai_family, &(sain6->sin6_addr), host, hostlen);
			snprintf( serv, servlen, "%d", ntohs(sain6->sin6_port) );
			return 0;
		};
		break;

		default:
		{
			return -1;
			break;
		}
	}
}

run && stdout

[root@localhost ctest]# 
[root@localhost ctest]# gcc addrinfo_ntop.c -o addrinfo_ntop
[root@localhost ctest]# 
[root@localhost ctest]# 
[root@localhost ctest]# ./addrinfo_ntop
addrinfo_ntop host/port = 58.251.150.157/8000	getnameinfo host/port = reverse.gdsz.cncnet.net/irdmi
addrinfo_ntop host/port = 112.90.143.245/8000	getnameinfo host/port = 112.90.143.245/irdmi

[root@localhost ctest]#