有关网络编程

1. 使用getaddrinfo获取主机IP，这种方法受系统，hostname与IP的绑定配置有关，最后不要用localhost，一般localhost配置的IP为127.0.0.1

　　另一种方法是使用getifaddress，没用过

int getIP(char *host, char *buf, int size)
{
	assert(host != NULL && buf != NULL);
	struct addrinfo hints;
	struct addrinfo *result, *rp;
	int s, sfd;

	memset(&hints, 0, sizeof(struct addrinfo));
	hints.ai_family = AF_INET;
	hints.ai_socktype = SOCK_STREAM;
	hints.ai_flags = AI_PASSIVE;// make sure this IP can do bind
	hints.ai_protocol = 0;
	hints.ai_canonname = NULL;
	hints.ai_addr = NULL;
	hints.ai_next = NULL;
	
	s = getaddrinfo(host, NULL, &hints, &result);
	if(s != 0)
	{
		fprintf(stderr, "Failed to get IP of %s: %s\n", host, gai_strerror(s));
		return -1;
	}
	for(rp = result; rp != NULL; rp = rp->ai_next)
	{
		sfd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
		if(sfd < 0) continue;
		s = bind(sfd, rp->ai_addr, rp->ai_addrlen);
		//inet_ntop(rp->ai_family, &((struct sockaddr_in *)rp->ai_addr)->sin_addr, buf, size);
		//DEBUG_PRINT("    ----ip IS %s\n", buf);
		close(sfd);
		if(s == 0) break;// we find one IP that can bind
	}
	if(rp != NULL)
	{
		// convert to ip str
		inet_ntop(rp->ai_family, &((struct sockaddr_in *)rp->ai_addr)->sin_addr, buf, size);
		DEBUG_PRINT("Got IP of %s is %s\n", host, buf);
	}
	// release buf
	freeaddrinfo(result);

	return (rp == NULL) ? -1 : 0;
}

2. Address already in use错误

　　写的一个py脚本需要多次listen在断开，但在第二次断开时，报了这个错。

　　因为TCP协议中有TIME_WAIT，要求端口在指定时间超时后才能再连接，避免后续的socket把先前尚未传送过来的包当做正常消息接受

　　可设置如下属性：sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)，这个要在绑定前调用，并且需要保证前次的bind相关的fd都close，否则会无效