Question

刚开始使用node.js编程并编写tcp套接字客户端。

我希望客户端连接到服务器。如果服务器不可用（即服务器在约定的端口上不存在），我希望客户端超时并在超时后重新连接。

我有这个代码，但它挂在第二个client.connect。怎么了？

var net = require('net');
var HOST = '127.0.0.1';
var PORT = 9000;
var client = new net.Socket();

client.connect(PORT, HOST, function(){
    console.log('CONNECTED TO: ' + HOST + ':' + PORT);
    client.write('I am Superman!');
});

client.on('error', function(e) {
    while (e.code == 'ECONNREFUSED') {
        console.log('Is the server running at ' + PORT + '?');`

        socket.setTimeout(1000, function() {
            console.log('Timeout for 5 seconds before trying port:' + PORT + ' again');
        }

        client.connect(PORT, HOST, function(){
            console.log('CONNECTED TO: ' + HOST + ':' + PORT);
            client.write('I am the inner superman');
        });
    }); 
});

更新的代码：

var net = require('net');
var HOST = '127.0.0.1';
var PORT = 9000;
var client = new net.Socket();

client.connect(PORT, HOST, function(){
    console.log('CONNECTED TO: ' + HOST + ':' + PORT);
    client.write('I am Superman');
});

client.on('error', function(e) {

    while (e.code == 'ECONNREFUSED') {
        console.log('Is the server running at ' + PORT + '?');

        client.setTimeout(4000, function() {

            client.connect(PORT, HOST, function() {
                console.log('CONNECTED TO: ' + HOST + ':' + PORT);
                client.write('I am inner Superman');
            });         

            console.log('Timeout for 5 seconds before trying port:' + PORT + ' again');
        });
    }
});

client.on('data', function(data) {
    console.log('DATA: ' + data);
    client.destroy();
});

client.on('close', function() {
    console.log('Connection closed');
});

使用更新的代码，超时似乎不会生效。当我启动此客户端而没有相应的服务器时，结果显示如下，没有4秒等待。

Is the server running at 9000?
Is the server running at 9000?
Is the server running at 9000?
Is the server running at 9000?
…

更新（咆哮错误的树？）

我回去查看socket.on（'error'）事件，发现错误后立即调用close事件。所以代码将关闭tcpclient而不等待4秒。有更好的想法吗？

Answer 1

你的超时是相反的。

应该是这样的：

var net = require('net');
var HOST = '127.0.0.1';
var PORT = 9000;
var client = new net.Socket();

client.connect(PORT, HOST, function(){
    console.log('CONNECTED TO: ' + HOST + ':' + PORT);
    client.write('I am Superman!');
});

client.on('error', function(e) {
    if(e.code == 'ECONNREFUSED') {
        console.log('Is the server running at ' + PORT + '?');

        client.setTimeout(4000, function() {
            client.connect(PORT, HOST, function(){
                console.log('CONNECTED TO: ' + HOST + ':' + PORT);
                client.write('I am the inner superman');
            });
        });

        console.log('Timeout for 5 seconds before trying port:' + PORT + ' again');

    }   
});
client.on('data', function(data) {
    console.log('DATA: ' + data);
    client.destroy();
});
client.on('close', function() {
    console.log('Connection closed');
});

超时后要运行的功能是回调。那就是等待执行的人。

此外，将while更改为if，在单个错误事件期间该条件不会更改。你的parens和括号不匹配。

Answer 2

根据我对已接受答案的评论，我发现使用.connect回调与'connect'侦听器的问题。每次调用.connect都会提示回调（添加一个监听器），即使连接失败也是如此。因此，当它最终连接所有那些回调被调用。因此，如果您使用.once('connect'..而不会发生这种情况。下面是我项目的客户端代码中的日志记录，这引起了我的观察。

ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
ENOENT
timeout
(node:21061) MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 connect listeners added. Use emitter.setMaxListeners() to increase limit  
^=== if you timeout and try .connect again eventually you hit this limit
ENOENT
timeout    <==== here is where the connection finally happens
connecting  <====  now all those listener callbacks fire.
connecting
connecting
connecting
connecting
connecting
connecting
connecting
connecting
connecting
connecting

所以请尝试以下版本

const net = require('net')
const HOST = '127.0.0.1'
const PORT = 9000
const client = new net.Socket()

const connect = () => {client.connect(PORT, HOST)}

client.once('connect', function(){
  console.log('CONNECTED TO: ' + HOST + ':' + PORT)
  client.write('I am Superman!')
})

client.on('error', function(e) {
  if(e.code == 'ECONNREFUSED') {
    console.log('Is the server running at ' + PORT + '?')
    console.log('Waiting for 5 seconds before trying port:' + PORT + ' again')
    setTimeout(connect,5000)
  }
})

connect()

client.on('data', function(data) {
  console.log('DATA: ' + data)
  client.destroy()
})
client.on('close', function() {
  console.log('Connection closed')
})

Nodejs - 让客户端套接字在5秒超时后再次尝试

2 个答案: