I just started using socket.io.js and am trying to get a function executed on the server as soon as I send a message to a client. My code is as follows,
server:
server.on('connection', onConnect);
var id = 0;
function onConnect(socket) {
socket.emit('myMsg', {id: ++id}, function () {console.log('id callback on server');});
}
client:
iosocket.on('myMsg', function(data, callback) {
console.log('id:', data.id, callback);
});
However I see that the callback function is displayed as 'undefined' on the client. From what I read on the docs I think this should work (https://github.com/LearnBoost/Socket.IO/wiki/Migrating-0.6-to-0.7+), so could someone please let me know what I am doing wrong here?
I think that the callback must be a function. Try this:
iosocket.on('myMsg', function(data, callback) {
console.log('id:', data.id);
callback();
});
See the acknowledgement section of the following link for an example:
http://socket.io/#how-to-use
if you would call callback as a function callback() on the client, it would activate your function on the server side, so it would console.log on your server.
if you just want to send a message from server to client, why make 2 callbacks? you can put it in data: {id:id,something:else).
if you want to log that something on the client;
if(data.something) {
console.log(data.something); //outputs "else"
}
Related
I'm using nodejs with expressjs for my api.
I want to call a function after res.json() is called.
for example the api fetches data to the client but i want to log that action but no need to make client wait for request response till the api saves log
module.exports = {
getAll:async function(req,res){
////fetch data from db
res.json({success:true,data:data});
module.exports.logthis();
return;
},
logthis: async function ()
{
//save log
}
}
is this true that logthis will not be interupted after return; is called ?
also is there a better pattern to do this, like a event queue listener so that i threw that request in a pool and it's executed whenever it's possible ?
Sending a json response to the client or using return statement will not stop the script from executing logthis function only if you put return statement before it.
module.exports = {
getAll:async function(req,res){
//fetch data from db
res.json({success:true,data:data});
this.logthis(data);
return;
},
logthis: function (data) {
// log data to file here
}
}
Remember that async function works in conjunction with await statement, if you don't have asynchronous functions inside getAll there is no need to use async keyword
You can simply use callback or promise instead.
function (data, callback){
DB.find(........)
callback(err,data)
// Do other stuff here.
}
Use
res.json({success:true,data:data}).then(function(){
//Enter your code here. res.json() has finished.
});
I am still learning node.js basics. My flow is like this,
browser<-->node<-->backend server doing calculation.
node and backend uses socket to communicate.
From the browser there are start/stop buttons to ask backend to start/stop the
calculation.
When node asks backend to start/stop, it must query to see if backend is
alive first.
My code is like this -
app.get('/stopCmd', function(req, res)
{
socketToBackendServer.write("status", function() {
console.log("Sending:", 'Node asking for STATUS');
});
socketToBackendServer.on("data", function() {
if(status is ok) // pseudo code
{
socketToBackendServer.write("stop", function() {
console.log("Sending:", 'Node sending STOP');
});
} else {
console.log("backend server is NOT ready");
}
});
});
app.get('/startCmd', function(req, res)
{
// do similar things as stopCmd
});
/////////////////////////////////////////////////
var socketToBackendServer = net.connect(2899);
function openSocket() {
socketToBackendServer.setKeepAlive(true);
socketToBackendServer.on('connect', onConnect.bind({}, socketToBackendServer));
socketToBackendServer.on('error', onError.bind({}, socketToBackendServer));
}
function onConnect(socket) {
var myData;
console.log('Socket is open!');
socket.on('data', function(data) {
console.log('Received:', data);
io.emit('time', { time: data.toJSON() });
});
}
function onError(socket) {
console.log('Socket error!');
// Kill socket
clearInterval(interval);
socket.destroy();
socket.unref();
// Re-open socket
setTimeout(openSocket, 1e3);
}
openSocket();
server.listen(7778);
if using the same browser, if i go crazy clicking start/stop... for the "
stopCmd", how to make sure when it queries "status", the response is caught
by its function, not "startCmd"'s ?
it's this line
socketToBackendServer.on("data", function()
Thank you again !
You can use multiple connections to the backend server, so one function can freely use one channel, the responses won't mix.
Or you can use a multiplexer function, that you call from both of your functions:
It could work if you can identify your requests, like you send and id with the status, for example socketToBackendServer.write("status 1", ... , and you send the id with the status response back from the backend server (if it yours). In this way you can send multiple requests at the same time, and when the response come, you can identify it, and call the callback function that you stored in an array with the ids.
You only send one request, and you wait for the response before you send another one. You must use a waiting queue, where you store the request, and the callback functions.
i want to send datas in same client (not all clients) with this code;
app.post("/search", function(req, res) {
//some other codes
//if database saved {
io.sockets.emit('preview-post', {title: "blabla" });// io variable was declared as GLOBAL
// } database saved end.
res.send({bla:bla});// response end before database saving process
});
this sample is working ! but it sends to all clients , How can i emit data to same opened browser(same client) ?
Second Question is: Are there any alternative ways to do this scenario?
My algorithm is post method fired > async call to an api > response end and page loaded on client > async call to an api is still continue > if async call is finished > send alert to client . But How? i wanted to do it wiht socket .io , if i use your 3.part , it'll work , can i do this scenario any other way?
This indeed sends to all sockets.
There are a couple ways to achieve what you are looking to do. The first way is to do something like this on the server:
io.on('connection', function(socket) {
socket.on('search', function(*/ client supplied arguments /*){
socket.emit('preview-post', {title: "blabla" });
});
});
If you are insistent on using a post request, and then sending it back to the client, there are two ways to achieve this.
The easiest way, if you only need to respond to this response, is just send a standard response from node, and let the client handle it:
res.send({
event: 'preview-post',
payload: {title: "blabla" }
});
This removes socket.io's event system, so if you are insistent on using socket.io to send this event back to the same client, you are going to need to use cookies. Express and the module cookie-parser make this easy for you.
Once you have this setup, inside your request you could do something like this:
app.post("/search", function(req, res) {
var socket = findSocketByCookie(req.cookies.myUniqueCookie);
socket.emit('preview-post', {title: "blabla" });
});
function findSocketByCookie(cookie) {
for(var i in io.sockets.connected) {
var socket = io.sockets.connected[i];
if(socket.handshake.headers.cookie.indexOf(cookie) !== -1){
return socket;
}
}
}
My server emits events properly, but the emit callback never works. In the following, nothing is logged on my console:
Server:
io.sockets.emit('delete hint', {id: id}, function(data){
console.log('callback');
});
Client:
socket.on('delete hint', function(data){
// display a message before deleting
$('#' + data.id).fadeOut(function(){
$(this).remove();
});
});
I've also tried the client side code as function(data, fn) in case the callback needed to be included on the receiving function.
I'm using windows and my command prompt shows the following when socket.io is emitting the event:
websocket writing 5:::{"name":"delete hint", "args":[{"id":"1"}, null]}
I can't figure out what the problem is, what am I doing wrong?
A callback is executed on the sender computer when the receiver computer calls it
Have a look at this code:
Server:
io.sockets.on('connection', connectionFunc);
function connectionFunc (socket) {
socket.emit('delete hint', "data for client", callThis);
}
//this function is executed when client calls it
function callThis (dataFromClient){
console.log("Call back fired: " + dataFromClient);
}
Client:
socket.on('delete hint', function(data, callback) {
console.log("i received: "+ data);
// call back will fire only when u the next line runs
callback("the callThis function on server will run");
});
You can do this the opposite way.
You need to call the callback.
socket.on('delete hint', function(data, cb){
// display a message before deleting
$('#' + data.id).fadeOut(function(){
$(this).remove();
cb(null, 'done');
});
});
I have been playing with Node.js for some time.
I have the following piece of script in my server:
socket.on('auth', function(uid, key) {
client.hgetall(uid, function (err, data) {
console.log(data);
if(key != data['key']) {
socket.disconnect();
}
this.user = data;
});
});
socket.on('loginGame', function(gameId) {
checkAuth();
console.log(user);
if(!games[gameId]) {
games[gameId] = {};
}
games[gameId][uid] = uid;
});
In my client;
socket.on('connect', function(){
socket.emit('auth', 1, 1);
socket.emit('loginGame', 1);
});
When I run this code, loginGame function finishes before auth function as I am doing I/O (using redis). I know this a feature of node.js, but I think I am missing something. How can I overcome this issue as auth function needs to finish before running any function. (I have a couple of more functions which need to run in serial)
I have found a node.js module: https://github.com/creationix/step . However, is this the only option? I think this is something most node.js developer might need. I am not that good at JS either.
What is the best and most elegant way of solving this issue?
Thanks,
Have the server send back an acknowledgement when auth is successful, and send loginGame in the handler for that message.