libevent进行dns解析

利用libevent非阻塞方式进行dns解析

代码如下：

#include <stdio.h>
#include <event2/util.h>
#include <event2/event.h>

#include <sys/socket.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

int n_pending_requests = 0;
struct event_base *base = NULL;

struct user_data
{
	char *name;
	int idx;
};

void call_back(int errcode, struct evutil_addrinfo *addr, void *ptr)
{
	struct user_data *data = ptr;
	const char *name = data->name;
	if(errcode)
	{
		printf("%d.%s->%s\n", data->idx, name, evutil_gai_strerror(errcode));
	}
	else
	{
		struct evutil_addrinfo *ai;
		printf("%d.%s", data->idx, name);
		if(addr->ai_canonname)
			printf("[%s]", addr->ai_canonname);
		puts("");
		for(ai = addr; ai; ai=ai->ai_next)
		{
			char buf[128];
			const char *s = NULL;
			if(ai->ai_family == AF_INET)
			{
				struct sockaddr_in *sin = (struct sockaddr_in*)ai->ai_addr;
				s = evutil_inet_ntop(AF_INET, &sin->sin_addr, buf, 128);
			}
			else if(ai->ai_family == AF_INET6)
			{
				struct sockaddr_in6 *sin6 = (struct sockaddr_in6*)ai->ai_addr;
				s = evutil_inet_ntop(AF_INET6, &sin6->sin6_addr, buf, 128);
			}
			if(s)
			{
				printf("  ---->%s\n", s);
			}
		}
		evutil_freeaddrinfo(addr);
	}
	free(data->name);
	free(data);
	if(--n_pending_requests == 0)
		event_base_loopexit(base, NULL);
}

int main(int argc, char *argv[])
{
    int i;
	struct evdns_base *dnsbase;
	if(argc ==1)
	{
		puts("NO address given.");
		return 0;
		
	}
	base = event_base_new();
	if(!base)
		return 1;
	dnsbase = evdns_base_new(base, 1);
	if(!dnsbase)
		return 2;
	for(i=1;i<argc;++i)
	{
		struct evutil_addrinfo hints;
		struct evdns_getaddrinfo_request *req;
		struct user_data *user_data;
		memset(&hints, 0, sizeof hints);
		hints.ai_family = AF_UNSPEC;
		hints.ai_flags = EVUTIL_AI_CANONNAME;
		hints.ai_socktype = SOCK_STREAM;
		hints.ai_protocol = IPPROTO_TCP;
		if(!(user_data = malloc(sizeof user_data)))
		{
			perror("malloc");
			exit(1);
		}
		if(!(user_data->name = strdup(argv[i])))
		{
			perror("strdup");
			exit(1);

		}
		user_data->idx = i;
		++n_pending_requests;
		req = evdns_getaddrinfo(dnsbase, argv[i], NULL, &hints, call_back, user_data);
		if(req == NULL)
			printf("[request for %s returned immediately]\n", argv[i]);
	}
	if(n_pending_requests)
	{
		event_base_dispatch(base);
	}
	evdns_base_free(dnsbase, 0);
	event_base_free(base);
    return 0;
}

gcc -g -o libevent_dns libevent_dns.c -levent

# ./libevent_dns www.baidu.com blog.youkuaiyun.com
1.www.baidu.com[www.a.shifen.COm]
  ---->220.181.111.188
  ---->220.181.112.244
2.blog.youkuaiyun.com
  ---->114.112.73.198