【Boost】boost库asio详解5——resolver与endpoint使用说明

转载地址：http://blog.csdn.net/huang_xw/article/details/8502895

tcp::resolver一般和tcp::resolver::query结合用，通过query这个词顾名思义就知道它是用来查询socket的相应信息，一般而言我们关心socket的东东有address，port而已，通过tcp::resolver很容易实现设置和查询，它通过query把字符串格式的ip如192.168.0.200或主机名http://localhost，端口“8080”等转化成socket内部表示格式，这样我们应用的时候可以直接使用字符串的形式，而且不用再担心socket的字节顺序转化问题。示例如下：

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boost::asio::io_service io_service ; boost::asio::ip::tcp::resolver resolver(io_service); boost::asio::ip::tcp::resolver::query query("localhost", "9000");

boost::asio::io_service io_service ;
boost::asio::ip::tcp::resolver resolver(io_service);
boost::asio::ip::tcp::resolver::query query("localhost", "9000");

还有要说明的是, boost::asio把通讯双方(server, client)都用endpoint的表示，所以endpoint中的address, port 分别封装了ip和端口。貌似resolver和endpoint不相干，于是乎出现tcp::resolver::iterator了，它是resolver的迭代器，其实就是endpoint的指针，那么就可以这样：

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boost::asio::ip::tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
boost::asio::ip::tcp::resolver::iterator end;
boost::system::error_code error = boost::asio::error::host_not_found;
boost::asio::ip::tcp::endpoint endpoint;
while (error && endpoint_iterator != end)
{
endpoint = *endpoint_iterator ;
socket.close();
socket.connect(endpoint, error);
endpoint_iterator++ ;
}

boost::asio::ip::tcp::resolver::iterator endpoint_iterator = resolver.resolve(query);
boost::asio::ip::tcp::resolver::iterator end;
boost::system::error_code error = boost::asio::error::host_not_found;
boost::asio::ip::tcp::endpoint endpoint;
while (error && endpoint_iterator != end)
{
endpoint = *endpoint_iterator ;
socket.close();
socket.connect(endpoint, error);
endpoint_iterator++ ;
}

得到endpoint后就好说啦，endpoint.address().to_string()就能够返回string格式的ip地址，endpoint.port()返回端口。

其实endpoint 完全可以自己构造，方法也是很简单的，tcp::endpoint(tcp::v4(), (unsigned short)9000) 这个是server端的用法，tcp::v4()直接返回自己的address，如果用于client那么需要设置server的ip ，实现如下：

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boost::system::error_code error = boost::asio::error::host_not_found; boost::asio::ip::address add; add.from_string("127.0.0.1"); tcp::endpoint endpoint(add, short(9000)); socket.connect(endpoint, error);

boost::system::error_code error = boost::asio::error::host_not_found;
boost::asio::ip::address add;
add.from_string("127.0.0.1");
tcp::endpoint endpoint(add, short(9000));
socket.connect(endpoint, error);

这样不使用resolver也是可以的。

还有更神奇的：

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boost::asio::io_service ioservice ;
boost::asio::io_service my_io_service ;
boost::asio::ip::tcp::resolver resolver(my_io_service);
boost::asio::ip::tcp::resolver::query query("www.google.com", "http");
boost::asio::ip::tcp::resolver::iterator iter = resolver.resolve(query);
boost::asio::ip::tcp::resolver::iterator end; // End marker.

while (iter != end)
{
boost::asio::ip::tcp::endpoint endpoint = *iter++;
std::cout << endpoint << std::endl;
}

boost::asio::io_service ioservice ;
boost::asio::io_service my_io_service ;
boost::asio::ip::tcp::resolver resolver(my_io_service);
boost::asio::ip::tcp::resolver::query query("www.google.com", "http");
boost::asio::ip::tcp::resolver::iterator iter = resolver.resolve(query);
boost::asio::ip::tcp::resolver::iterator end; // End marker.

while (iter != end)
{
boost::asio::ip::tcp::endpoint endpoint = *iter++;
std::cout << endpoint << std::endl;
}

这样有发现一个新的用途，通过resolver迭代可以得到多个节点endpoint，比如google 就有好几个ip。

上面这个例子的运行结果:

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74.125.128.106:80
74.125.128.147:80
74.125.128.99:80
74.125.128.103:80
74.125.128.104:80
74.125.128.105:80