node.js eventEmitter + http.request - node.js

i did this tutorial node.js eventEmitter, it worked nicely. I added a method that uses http.request to get data, which works and emit the data.
the problem is that the listener doesn't catch the event !
can someone help ?
code :
var events = require('events');
var util = require('util');
var http = require('http');
//http request options, it query the twitter api and get the public timeline, works!
var options = {
hostname : 'api.twitter.com',
port : 80,
method : 'get',
path : '/1/statuses/public_timeline.json?count=3&include_entities=true'
}
// The Thing That Emits Event
Eventer = function(){
events.EventEmitter.call(this);
//tutorial examples
this.kapow = function(){
var data = "BATMAN"
this.emit('blamo', data);
}
//tutorial examples
this.bam = function(){
this.emit("boom");
}
//my method
this.GetTweetList = function(){
var tweets = "";
var req = http.request(options, function(response){
var body = "";
response.on('data',function(data){
body += data;
});
response.on('end', function(){
tweets = JSON.parse(body);
this.emit("tweets", tweets);
util.puts('!!!!!!!!!! got some data !!!!!!!!!! \n');
});
});
req.end();
}
};
util.inherits(Eventer, events.EventEmitter);
// The thing that listens to, and handles, those events
Listener = function(){
//tutorial examples
this.blamoHandler = function(data){
console.log("** blamo event handled");
console.log(data);
},
//tutorial examples
this.boomHandler = function(data){
console.log("** boom event handled");
}
//my listener method
this.GetTweetListHandler = function(data){
console.log("** tweets event handled");
util.put(data);
util.puts('!!!!!!!!!! got some data in listener !!!!!!!!!! \n');
}
};
// The thing that drives the two.
//instanciating the object and liking the methodes
var eventer = new Eventer();
var listener = new Listener(eventer);
eventer.on('blamo', listener.blamoHandler);
eventer.on('boom', listener.boomHandler);
eventer.on('tweets', listener.GetTweetListHandler);
//calling the methodes
eventer.kapow();//works
eventer.bam();//works
setInterval(eventer.GetTweetList, 2000);
//eventer.GetTweetList();// still waiting but the eventer display that he got the data

Hard one to spot ...
The problem is the this pointer from this.emit("tweets", tweets);. You are doing this call from within an anonymous callback passed to response.on, so this does not represent the Eventer object that you created.
To solve it, you need to "save" the this pointer (a common practice).
var tweets = "";
var self = this;
....
self.emit("tweets", tweets);

Related

publisher subscribber pattern in nodejs sampel code is not woring with out setinterval

I am trying to implement pub/sub as shown below
publisher.js
var zmq = require('zmq');
var pub = zmq.socket('pub');
pub.bindSync('tcp://127.0.0.1:5555');
pub.send('pub msg');
/*
setInterval(function(){
console.log("sending message")
},500);*/
subscriber.js
var zmq = require('zmq');
var sub = zmq.socket('sub');
sub.connect('tcp://127.0.0.1:5555');
sub.subscribe(''); //herein lies the question
sub.on('message',function(msg){
console.log('Received msg:',msg);
})
the above subscriber will receive the message only when pub.send('pub msg'); is inside setInterval not sure about my understanding
I dont want use setInterval rather i have to send the message as soon it arrives
Please say how can i do it using pub/sub only i guess there is some basic understanding missing please help
in nodejs code i am trying using a route has
router.post('/putMsgIn0MQ', function (req, res, next) {
pushData(JSON.stringify(req.body))
})
var pushData = function(dataToPush) {
var zmqSocket = zmq.socket('pub')
var zmqPortPart = 'tcp://127.0.0.1:5555'
zmqSocket.bind(zmqPortPart);
zmqSocket.send(dataToPush);
}
subscriber
var sub = zmq.socket('sub');
sub.connect('tcp://127.0.0.1:5555');
sub.subscribe(''); //herein lies the question
console.log('Received msg:');
sub.on('message',function(msg){
console.log('Received msg:');
console.log(msg.toString())
var jsonPayload = msg.toString();
processData(jsonPayload, zmqPortObj.name);
})
Based on this code, from their documentaiton:
// pubber.js
var zmq = require('zmq')
, sock = zmq.socket('pub');
sock.bindSync('tcp://127.0.0.1:3000');
console.log('Publisher bound to port 3000');
setInterval(function(){
console.log('sending a multipart message envelope');
sock.send(['kitty cats', 'meow!']);
}, 500);
It seems that setInterval is just utility function :)
What is preventing that you fire it manually?
So for example, imaginary controller:
exports.animals= {
getCat: function (request, response) {
var animal = request.payload.catStuff;
//process the animal object
//and manually fire the message like:
sock.send(['kitty cats', 'meow!']);
...

Socket.IO server not receiving message from client

I'm playing around with Node, Socket.IO and BDD by creating a chat application. During one of the tests, I get a timeout error stating:
Error: timeout of 2000ms exceeded. Ensure the done() callback is being called in this test.
The affected test is
it('#must be able to receive a message', function(done)
{
chatterServer.on('chatterMessage', function(data)
{
console.log('Incoming message!');
expect(data).to.have.property('message');
expect(data.message).to.be('Hello, world!');
done();
});
console.log('Sending message!');
chatterClient.send('chatterMessage', { message: 'Hello, world!' });
console.log('Sent!');
});
I found that the cause of this issue is that the chatterMessage event is not being caught by the server. Whilst I did specify it.
The console's output is:
Sending message!
Sent!
Error: timeout of 2000ms exceeded. Ensure the done() callback is being called in this test.
I'm probably doing something wrong. I'm not too familiar with Node and Socket.IO, so I'm sorry if this question is very obvious.
I looked around Google with the search terms 'socket.io server not receiving from client', but from what I found, nothing helped me to solve my issue so far.
I did however try the solution in this question, but that didn't fix it for me.
I'm using Mocha and expect.js
The complete test is:
var util = require('util');
var Chatter = require('../src/index');
var ChatterServer = Chatter.Server;
var ChatterClient = Chatter.Client;
var express = require('express');
var expect = require('expect.js');
var socketIO = require('socket.io');
var socketIOClient = require('socket.io-client');
var host = 'http://localhost';
var port = 8080;
describe('Chatter', function()
{
'use strict';
var chatterServer;
var chatterClient;
var server;
before(function()
{
var app = express();
server = app.listen(port);
});
beforeEach(function()
{
chatterServer = new ChatterServer(socketIO(server));
chatterClient = new ChatterClient(socketIOClient, util.format('%s:%s', host, port.toString()));
});
...
it('#must be able to receive a message', function(done)
{
chatterServer.on('chatterMessage', function(data)
{
console.log('Incoming message!');
expect(data).to.have.property('message');
expect(data.message).to.be('Hello, world!');
done();
});
console.log('Sending message!');
chatterClient.send('chatterMessage', { message: 'Hello, world!' });
console.log('Sent!');
});
});
My Client (ChatterClient) is:
(function()
{
'use strict';
function Client(socketIO, url)
{
this.socketIO = socketIO(url);
}
Client.prototype.send = function(event, data)
{
this.socketIO.emit(event, data);
};
Client.prototype.on = function(event, callback)
{
this.socketIO.on(event, callback);
};
if (module !== undefined && module.hasOwnProperty('exports')) {
module.exports = Client;
} else {
window.Chatter = {
Client: Client,
};
}
}());
The Server (ChatterServer) is:
(function()
{
'use strict';
function Server(socketIO)
{
this.socketIO = socketIO;
this.connectedUsers = {};
this.on('connection', (function(user)
{
var userID = user.client.id;
this.connectedUsers[userID] = user;
user.emit('chatterConnectionAcknowledged', { id: userID });
}).bind(this));
}
Server.prototype.on = function(event, handler)
{
this.socketIO.on(event, handler);
};
module.exports = Server;
}());
You need to change your code in two sides.
First side, you will need to listen incoming socket connections on the socketIO object. (see the emphasized code below)
//.. some code
function Server(socketIO)
{
this.socketIO = socketIO;
this.connectedUsers = {};
this.socketIO.on('connection', (function(user)
{
var userID = user.client.id;
this.connectedUsers[userID] = user;
user.emit('chatterConnectionAcknowledged', { id: userID });
}).bind(this));
}
//.. some code
Second side, when you are adding new events to listen on the server, you need to bind those events to the sockets since they are ones that are going to listen when events are emitted from the socket clients.
Server.prototype.on = function (event, handler) {
Object.keys(this.connectedUsers).map(function (key) {
this.connectedUsers[key].on(event, handler);
}.bind(this));
};

node.js server handle request callback function ending before writing response

I have an http server with a handleRequest callback that runs another script in vm.runInNewContext for each request. The script that runs inside vm.runInNewContext makes some asynchronous http post requests and writes the server response only after getting the responses from the posts.
As a result, the code of handleRequest callback ends before the server response is written.
Is it safe? or is there a way to avoid this situation?
Here is some code:
var server = http.createServer(handleRequest);
server.listen(8080);
var handleRequest = function (request, response) {
// get request data...
var context = {
ServerRequest : request,
ServerResponse : response
};
var stringScript = // a string with the script that posts data
var script = vm.createScript(stringScript);
script.runInNewContext({ context: context });
}
the script string does this:
var request = require('request');
var options = {....}
var req = request.get(options);
req.on('response', function (res) {
var chunks = [];
res.on('data', function(chunk) {
chunks.push(chunk);
});
res.on('end', function() {
var buffer = Buffer.concat(chunks);
var encoding = res.headers['content-encoding'];
if (encoding == 'gzip') {
zlib.gunzip(buffer, function(err, decoded) {
// set response headers and write the response
context.ServerResponse.end(decoded.toString());
});
} else if (encoding == 'deflate') {
zlib.inflate(buffer, function(err, decoded) {
// set response headers and write the response
context.ServerResponse.end(decoded.toString());
})
} else {
// set response headers and write the response
context.ServerResponse.end(buffer.toString());
}
});
});
Simple solution: Return a promise (e.g. use the Q-library) from the VM-script.
script.runInNewContext will return whatever you return from the VM-script. That way you have a "callback" for when the VM code finishes.
// Script for VM
// I simplified it. Just resolve or reject the promise whenever you are done with your work
'use strict';
var defer = q.defer();
doABarrelRoll(function() {
defer.resolve('RESULT');
});
defer.promise; // This line will return the promise.
When returning a value from a VM-script, you do not need any return construction. Just write the thing you want and let the magic happen.
// Script for current context
'use strict';
var server = http.createServer(handleRequest);
server.listen(8080);
var handleRequest = function (request, response) {
// get request data...
var context = {
ServerRequest : request,
ServerResponse : response
};
var stringScript = // a string with the script that posts data
var script = vm.createScript(stringScript);
var prom = script.runInNewContext({
context: context,
q: require('q'),
});
prom.done(function ($result) {
console.log('VM finished with result: ' + $result);
});
}

RxJS + node.js HTTP server implementation?

I 've been well with node.js until RxJS implementation.
Here is my trial code studying-
Reactive-Extensions / rxjs-node
https://github.com/Reactive-Extensions/rxjs-node
rx_http.js
(RxJS wrapper of the http lib of node.js)
var Rx = require("./rx.min");
var http = require("http");
for(var k in http)
{
exports[k] = http[k];
}
exports.createServer = function ()
{
var subject = new Rx.AsyncSubject();
var observable = subject.asObservable();
observable.server = http.createServer(function (request, response)
{
subject.onNext({ request:request, response:response });
subject.onCompleted();
});
return observable;
};
server.js
var http = require('./rx_http');
// rxServer
var serverObservable = http.createServer();
var port = 3000;
serverObservable.server.listen(port);
console.log("Server listening on port: "+port);
// HTTP request event loop function
serverObservable.subscribe(function (data)
{
var req = data.request;
console.log(req.headers);
var res = data.response;
res.writeHead(200, {'Content-Type':"text/html"});
res.end("hello world");
console.log("res content out");
});
// exceptiopn
process.on('uncaughtException', function (err)
{
console.log(['Caught exception:', err.message].join(" "));
});
The code ends up with one-time 'hello world' output to browser, and the RxServer stops reacting to another access (brwoser reload etc.).
I'm on the way to learn RxJS thing, but few documentation found on the web.
Tell me what's wrong with the code, and if you know better implementations, please share.
Thank you.
Use Rx.Subject instead of Rx.AsyncSubject in rx_http.js.
AsyncSubject caches the last value of onNext() and propagates it to the all observers when completed. AsyncSubject
exports.createServer = function ()
{
var subject = new Rx.Subject();
var observable = subject.asObservable();
observable.server = http.createServer(function (request, response)
{
subject.onNext({ request:request, response:response });
});
return observable;
};
Calling oncompleted on the subject when the first request arrives ends the observable sequence. Could you please remove that line an try again.
I hope it helps.
Ahmet Ali Akkas

Node.js My Request is Not Blocking

I'm new to node.js, and I'm trying to call a service, parse its data and return it as part of a view. I can't seem to get the request to block until the response is complete. The console always logs 'wrong' before 'right' (returning the 1,2,3 array). What am I missing?
app.js
var reading = require('./reading');
app.get('/reading', function(req, res){
res.render('reading/index.stache',
{
locals : { ids : reading.list},
partials : {
list : '{{#ids}}{{.}}<br />{{/ids}}'
}
});
});
reading.js
var request,
http = require('http'),
host = 'google.com',
path ='/';
var list = function(){
var connection = http.createClient(80, host),
request = connection.request(path);
request.addListener('response', function(response){
var data = '';
response.addListener('data', function(chunk){
data += chunk;
});
response.addListener('end', function(){
console.log('right')
//var results = JSON.parse(data);
// i need results from json
return [88234,883425,234588];
});
});
request.end();
console.log('wrong');
return [1,2,3];
}
module.exports.list = list;
Of course you can't get the request to block until the response is back.
That's because there is communication latency between sending the request of and getting the response back. It would be stupid to wait and do nothing whilst that latency is happening.
Use callbacks and asynchronous control flow.
var list = function(callback){
var connection = http.createClient(80, host),
request = connection.request(path);
request.addListener('response', function(response){
var data = '';
response.addListener('data', function(chunk){
data += chunk;
});
response.addListener('end', function(){
console.log('right')
// USE A CALLBACK >:(
callback([88234,883425,234588]);
});
});
request.end();
}
If you wan't to run anything in sync have a look at the sync module. It's based on fibers.

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