如何在Java中确定服务器是否关闭连接(接收到RST数据包)

Question

我使用Socket类进行TCP连接。但我目前的问题是确定断开的确切原因。在这两种情况下（如果存在连接超时或服务器关闭连接），我都会收到带有"Broken pipe"消息的SocketException。那么我如何才能准确地确定断开连接的原因呢？

谢谢！

Answer 1

我认为应该抛出一个不同的Exception。如果你谈论的是一个连接，那么你应该从一个主机获得一个SocketException，它会发送一个重置（我认为这是RST数据包），如果你的连接超时，则应该获得SocketTimeoutException。

如果您再次谈论IO，如果服务器断开连接，您将获得SocketException，而如果IO超时（可能只是读取），您将得到SocketTimeoutException。

这是我使用的测试程序。当然，我正在疯狂地流眼窝的血。

    try {
        new Socket().connect(new InetSocketAddress(someIpThatHangs, 8000), 1000);
        fail("Should have thrown");
    } catch (SocketTimeoutException e) {
        // we expected it to timeout
    }
    try {
        new Socket().connect(new InetSocketAddress(someIpThatResets, 1000));
        fail("Should have thrown");
    } catch (SocketException e) {
        // we expected it to throw an exception immediately on reset
    }
    // start our server
    final ServerSocket serverSocket = new ServerSocket();
    int serverPort = 8000;
    InetSocketAddress address = new InetSocketAddress("127.0.0.1", serverPort);
    serverSocket.bind(address);
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            while (!Thread.currentThread().isInterrupted()) {
                try {
                    Socket clientSocket = serverSocket.accept();
                    System.err.println("Got a connection");
                    Thread.sleep(1000);
                    clientSocket.close();
                } catch (InterruptedException e) {
                    return;
                } catch (Exception e) {
                    e.printStackTrace();
                    return;
                }
            }
        }
    });
    thread.start();
    // wait for the server to start
    Thread.sleep(100);
    Socket clientSocket = new Socket();
    clientSocket.connect(address);
    try {
        // read until the server closes the connection
        clientSocket.getInputStream().read();
    } catch (SocketException e) {
        // expected socket exception
    }
    clientSocket = new Socket();
    clientSocket.connect(address);
    clientSocket.setSoTimeout(100);
    try {
        // read until the socket timeout expires
        clientSocket.getInputStream().read();
    } catch (SocketTimeoutException e) {
        // expected read timeout exception
    }
    serverSocket.close();
    thread.interrupt();