Question

基本上我有一个 db.test.message 集合，只有字段 _id 和文字

客户端将已打印的消息数发送到服务器（前0），如果 db.test.messages.count（）大于此数，则仅发送新消息（或文件），如果不是，则服务器等待直到创建新消息。它一遍又一遍地重复这个操作。

首先正确打印所有邮件，但第二次请求时出错（localhost：3000 / messages？num_of_messages = 3）

Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:335:11)
at ServerResponse.writeHead (_http_server.js:195:21)
at c:\nodejs\myapp\app.js:41:30
at handleCallback (c:\nodejs\node_modules\mongodb\lib\utils.js:95:12)
at c:\nodejs\node_modules\mongodb\lib\cursor.js:590:16
at handleCallback (c:\nodejs\node_modules\mongodb\node_modules\mongodb-core\lib\cursor.js:234:5)
at setCursorDeadAndNotified (c:\nodejs\node_modules\mongodb\node_modules\mongodb-core\lib\cursor.js:424:3)
at nextFunction (c:\nodejs\node_modules\mongodb\node_modules\mongodb-core\lib\cursor.js:586:7)
at Cursor.next (c:\nodejs\node_modules\mongodb\node_modules\mongodb-core\lib\cursor.js:614:3)
at fetchDocs (c:\nodejs\node_modules\mongodb\lib\cursor.js:586:10)

我使用了这个例子并将其改为我的需要： http://www.stoimen.com/blog/2010/12/02/diving-into-node-js-a-long-polling-example/

我知道我在使用 response.end（）之后尝试写 response.wirte ，但根据上面的示例和我的代码＆＃39 ;除非发生一些我不知道的异步执行，否则不可能发生。

这是客户端代码：

$(function () {
            $('#ready').append('ready');

            function check_for_new_messages(num_of_messages) {
                $.ajax({
                    cache: false,
                    // setup the server address
                    url: '/messages?num_of_messages=' + num_of_messages,
                    data: {},
                    success: function (response, code, xhr) {

                        if (response.no_new_messages) {
                            check_for_new_messages(num_of_messages);
                            return false;
                        }

                        // do whatever you want with the response
                        var msgs = response;
                        for (var i = 0; i < msgs.length; i++) {
                            $('#messages').append(msgs[i]._id + ',' + msgs[i].text + '<br/>');
                        }
                        // make new call
                        check_for_new_messages(num_of_messages + msgs.length);
                    }
                });
            }
            check_for_new_messages(0);
        });

服务器端代码：

var http = require("http"), fs = require("fs"), url = require('url');

http.createServer(function (request, response) {
   var parameters = url.parse(request.url, true).query;
   var num_of_messages = parseInt(parameters.num_of_messages);
   check_for_new_messages(new Date(), num_of_messages, request, response);
}).listen(80);

function check_for_new_messages(startingTime, num_of_messages, request, response) {
var date = new Date();
if (date - startingTime >= 60000) {
    response.writeHead(200, {
        'Content-Type': 'application/json',
        'Access-Control-Allow-Origin': '*'
    });
    response.write('{no_new_messages: true}', 'utf8');
    response.end();
    return false;
}

var mongoClient = require('mongodb').MongoClient;
mongoClient.connect("mongodb://localhost:27017/test", function (err, db) {
    var c = db.collection('message');
    c.count(function (err, count) {
        if (count > num_of_messages) {
            c.find({_id: {$gt: num_of_messages}}).toArray(function (err, items) {
                var str_items = JSON.stringify(items);
                response.writeHead(200, {
                    'Content-Type': 'application/json',
                    'Access-Control-Allow-Origin': '*'
                });
                response.write(str_items, 'utf8');
                response.end();
                return false;
            });
        }
    });
});

setTimeout(function () {
    check_for_new_messages(startingTime, num_of_messages, request, response)
}, 10000);

}

感谢您的时间。

尝试与Node.js和Mongodb进行简单的长轮询聊天

0 个答案: