知识问答

在localhost上，如何选择空闲端口号？

内容 隐藏
问题：在localhost上，如何选择空闲端口号？
回答 0
回答 1
回答 2
回答 3
回答 4

问题：在localhost上，如何选择空闲端口号？

我正在尝试进行进程间通信，并且由于无法弄清楚如何在Windows下使用命名管道，因此我认为我将使用网络套接字。一切都发生在本地。服务器能够在单独的进程中启动从属服务器，并在某些端口上进行侦听。奴隶完成工作并将结果提交给主人。如何确定哪个端口可用？我假设我无法在端口80或21上收听？

我正在使用Python，如果这样做会减少选择的余地。

谢谢！

点击查看英文原文

I’m trying to play with inter-process communication and since I could not figure out how to use named pipes under Windows I thought I’ll use network sockets. Everything happens locally. The server is able to launch slaves in a separate process and listens on some port. The slaves do their work and submit the result to the master. How do I figure out which port is available? I assume I cannot listen on port 80 or 21?

I’m using Python, if that cuts the choices down.

Thanks!

回答 0

不要绑定到特定端口，也不要绑定到端口0，例如sock.bind(('', 0))。然后，操作系统将为您选择一个可用端口。您可以使用来获得选择的端口sock.getsockname()[1]，并将其传递给从站，以便它们可以重新连接。

点击查看英文原文

Do not bind to a specific port, or bind to port 0, e.g. sock.bind(('', 0)). The OS will then pick an available port for you. You can get the port that was chosen using sock.getsockname()[1], and pass it on to the slaves so that they can connect back.

回答 1

为了简要说明上面的解释：

import socket
from contextlib import closing

def find_free_port():
    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
        s.bind(('', 0))
        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        return s.getsockname()[1]
点击查看英文原文

For the sake of snippet of what the guys have explained above:

import socket
from contextlib import closing

def find_free_port():
    with closing(socket.socket(socket.AF_INET, socket.SOCK_STREAM)) as s:
        s.bind(('', 0))
        s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
        return s.getsockname()[1]

回答 2

将套接字绑定到端口0。将选择一个从1024到65535的随机空闲端口。您可以在getsockname()之后紧跟着检索选定的端口bind()。

点击查看英文原文

Bind the socket to port 0. A random free port from 1024 to 65535 will be selected. You may retrieve the selected port with getsockname() right after bind().

回答 3

您可以在任何端口上侦听；通常，用户应用程序应侦听端口1024及更高端口（通过65535）。如果您的侦听器数量可变，那么最主要的事情就是为您的应用分配一个范围-例如20000-21000和CATCH EXCEPTIONS。这样，您将知道计算机上端口是否不可用（换句话说，由另一个进程使用）。

但是，就您而言，只要绑定失败时打印错误消息，就可以为侦听器使用单个硬编码端口，这不会有问题。

还要注意，您的大多数套接字（用于从属）不需要显式绑定到特定的端口号-仅需要将等待传入连接的套接字（例如此处的主机）设置为侦听器并绑定到端口。如果在使用套接字之前未为端口指定端口，则操作系统将为该套接字分配可用端口。当主机希望响应从机发送数据时，当侦听器接收数据时，可以访问发送者的地址。

我想您将为此使用UDP？

点击查看英文原文

You can listen on whatever port you want; generally, user applications should listen to ports 1024 and above (through 65535). The main thing if you have a variable number of listeners is to allocate a range to your app – say 20000-21000, and CATCH EXCEPTIONS. That is how you will know if a port is unusable (used by another process, in other words) on your computer.

However, in your case, you shouldn’t have a problem using a single hard-coded port for your listener, as long as you print an error message if the bind fails.

Note also that most of your sockets (for the slaves) do not need to be explicitly bound to specific port numbers – only sockets that wait for incoming connections (like your master here) will need to be made a listener and bound to a port. If a port is not specified for a socket before it is used, the OS will assign a useable port to the socket. When the master wants to respond to a slave that sends it data, the address of the sender is accessible when the listener receives data.

I presume you will be using UDP for this?

回答 4

如果您只需要找到一个空闲端口供以后使用，这是一个类似于先前答案的代码段，但使用socketserver则更短：

import socketserver

with socketserver.TCPServer(("localhost", 0), None) as s:
    free_port = s.server_address[1]

请注意，不能保证端口保持空闲状态，因此您可能需要将此代码段和使用它的代码放入循环中。

点击查看英文原文

If you only need to find a free port for later use, here is a snippet similar to a previous answer, but shorter, using socketserver:

import socketserver

with socketserver.TCPServer(("localhost", 0), None) as s:
    free_port = s.server_address[1]

Note that the port is not guaranteed to remain free, so you may need to put this snippet and the code using it in a loop.