server.listen()

启动监听连接的服务器。 net.Server 可以是 TCP 或 IPC 服务器，这取决于它监听什么。

可能的语法有：

此函数是异步的。当服务器开始监听时，将触发 'listening' 事件。最后一个参数 callback 将被添加为 'listening' 事件的监听器。

所有 listen() 方法都可以采用 backlog 参数来指定待处理连接队列的最大长度。实际长度将由操作系统通过 sysctl 设置确定，例如 Linux 上的 tcp_max_syn_backlog 和 somaxconn。此参数的默认值为 511（不是 512）。

所有 net.Socket 都设置为 SO_REUSEADDR（详见 socket(7)）。

当且仅当在第一次调用 server.listen() 期间出现错误或调用 server.close() 时，才能再次调用 server.listen() 方法。否则，将抛出 ERR_SERVER_ALREADY_LISTEN 错误。

监听时最常见的错误之一是 EADDRINUSE。当另一个服务器已经在监听请求的 port/path/handle 时会发生这种情况。处理此问题的方法之一是在一定时间后重试：

server.on('error', (e) => {
  if (e.code === 'EADDRINUSE') {
    console.log('Address in use, retrying...');
    setTimeout(() => {
      server.close();
      server.listen(PORT, HOST);
    }, 1000);
  }
});

Start a server listening for connections. A net.Server can be a TCP or an IPC server depending on what it listens to.

Possible signatures:

server.listen(handle[, backlog][, callback])
server.listen(options[, callback])
server.listen(path[, backlog][, callback]) for IPC servers
server.listen([port[, host[, backlog]]][, callback]) for TCP servers

This function is asynchronous. When the server starts listening, the 'listening' event will be emitted. The last parameter callback will be added as a listener for the 'listening' event.

All listen() methods can take a backlog parameter to specify the maximum length of the queue of pending connections. The actual length will be determined by the OS through sysctl settings such as tcp_max_syn_backlog and somaxconn on Linux. The default value of this parameter is 511 (not 512).

All net.Socket are set to SO_REUSEADDR (see socket(7) for details).

The server.listen() method can be called again if and only if there was an error during the first server.listen() call or server.close() has been called. Otherwise, an ERR_SERVER_ALREADY_LISTEN error will be thrown.

One of the most common errors raised when listening is EADDRINUSE. This happens when another server is already listening on the requested port/path/handle. One way to handle this would be to retry after a certain amount of time:

server.on('error', (e) => {
  if (e.code === 'EADDRINUSE') {
    console.log('Address in use, retrying...');
    setTimeout(() => {
      server.close();
      server.listen(PORT, HOST);
    }, 1000);
  }
});