通常作为客户端从哪个源端口发送数据并不重要,但我仍然想做一些测试。 因此,我尝试将客户端的套接字绑定(bind)到特定端口,但即使我在本地计算机上运行客户端和服务器(使用 localhost 作为目标地址),服务器也会告诉我源端口类似于 59000。 我这样初始化套接字:
tcp::socket socket(io_service,tcp::endpoint(tcp::v4(),2000));
是否可以按照我的意图进行? 我试图找出我的路由器在消息通过时是否更改了端口。 那就是我目前正在玩的 NAT 遍历东西。
最佳答案
可以完全按照问题中的说明将套接字绑定(bind)到特定端口:
using boost::asio::ip::tcp;
boost::asio::io_service io_service;
tcp::socket socket(io_service, tcp::endpoint(tcp::v4(), 2000));
assert(socket.local_endpoint().port() == 2000); // true
在这种情况下,socket
对象将为 constructed ,打开并绑定(bind)到本地endpoint地址为 INADDR_ANY
,端口为 2000
。
由于连接的建立方式,本地端点可能会发生变化。当从 socket.connect()
启动连接操作时或 socket.async_connect()
成员函数,套接字将尝试连接到远程端点,必要时打开套接字。因此,当在已经打开的套接字上调用时,套接字的本地端点不会改变。
另一方面,当连接操作从 connect()
启动时或 async_connect()
免费功能,在尝试连接到任何端点之前关闭套接字。因此,套接字将绑定(bind)到一个未指定的端口。自由函数文档的参数部分定义了这种行为:
The
socket
to be connected. If thesocket
is already open, it will be closed.
此外,没有干净的方法来控制这种行为,因为 socket.close()
和 socket.connect()
成员函数在内部一个接一个地被调用implementation .
这是一个完整的示例,演示了上述行为:
#include <iostream>
#include <boost/asio.hpp>
#include <boost/bind.hpp>
#include <boost/lexical_cast.hpp>
// This example is not interested in the handlers, so provide a noop function
// that will be passed to bind to meet the handler concept requirements.
void noop() {}
// Helper function used to initialize the client socket.
void force_endpoint(boost::asio::ip::tcp::socket& client_socket)
{
using boost::asio::ip::tcp;
client_socket.close();
client_socket.open(tcp::v4());
client_socket.bind(tcp::endpoint(tcp::v4(), 2000));
std::cout << "client socket: " << client_socket.local_endpoint()
<< std::endl;
}
int main()
{
using boost::asio::ip::tcp;
boost::asio::io_service io_service;
// Create all I/O objects.
tcp::acceptor acceptor(io_service, tcp::endpoint(tcp::v4(), 0));
tcp::socket server_socket(io_service);
tcp::socket client_socket(io_service);
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Initiate the connect operation directly on the socket.
server_socket.close();
force_endpoint(client_socket);
acceptor.async_accept(server_socket, boost::bind(&noop));
client_socket.async_connect(acceptor.local_endpoint(), boost::bind(&noop));
// Print endpoints before and after running the operations.
io_service.run();
std::cout << "After socket.async_connect(): "
<< client_socket.local_endpoint() << std::endl;
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
// Initiate the connection operation with the free async_connect function.
server_socket.close();
force_endpoint(client_socket);
acceptor.async_accept(server_socket, boost::bind(&noop));
boost::asio::async_connect(
client_socket,
tcp::resolver(io_service).resolve(
tcp::resolver::query("127.0.0.1",
boost::lexical_cast<std::string>(acceptor.local_endpoint().port()))),
boost::bind(&noop));
// Run the service, causing the client to connect to the acceptor.
io_service.reset();
io_service.run();
std::cout << "After async_connect(): "
<< client_socket.local_endpoint() << std::endl;
}
产生了以下输出:
client socket: 0.0.0.0:2000
After socket.async_connect(): 127.0.0.1:2000
client socket: 0.0.0.0:2000
After async_connect(): 127.0.0.1:53115
关于sockets - 无法使用 boost asio 设置 TCP 源端口,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23752798/