JS Closures, Redis, loop, Async :: empty array - node.js

I give up on this. May some of the wise stackoverflow monks please fix my bugs?
Code is self explaining. Client sends room names, server does a redis lookup and pushes valid rooms to the array. After adding all the rooms, the list should be emitted to the client.
Problem is closure, async etc. based. I understand the problem but cannot get a workaround because the array needs to remain inside the function. Tricky.
Code:
function roomList(socket){
var roomlist = [], rooms = getRooms(), p = /pChannel_/;
redis.select(7, function(err,res){
for (var k in rooms){
if(rooms[k] != '' && p.test(rooms[k])){
var key = 'channel:'+rooms[k];
redis.hgetall(key, function (err, reply) {
if(reply){
var c = io.sockets.manager.rooms[rooms[k]];
roomlist.push( Array(reply['name'],c.length,reply['icon']) );
}
else { console.log('nothing found'); }
});
}
}
// here be dragons
console.log(roomlist);
socket.emit('roomList', roomlist);
});
}
Thanks.

C'mon guys. The OP explicitly said she/he is interested by understanding how things are supposed to work. And you don't need Q or async or any other 3rd party modules to implement this.
In the initial code, there are two problems:
with Javascript, the closure scope is at function level, not block level. A function must be introduced to define a proper closure. Here, a simple forEach can be used.
the final step (i.e. emit) is not run after the replies have been received from Redis. It must be called in the loop itself. In order to achieve it, it is required to count the items so that the inner callback can test whether the process is complete or not.
So here is another version:
function roomList(socket){
var roomlist = [], rooms = getRooms(), p = /pChannel_/;
redis.select(7, function(err,res){
var count = rooms.length
rooms.forEach( function(r) {
if( r != '' && p.test(r) ) {
var key = 'channel:'+r
redis.hgetall(key, function (err, reply) {
if(reply) {
var c = io.sockets.manager.rooms[r];
roomlist.push( Array(reply['name'],c.length,reply['icon']) );
} else {
console.log('nothing found');
}
if ( --count <= 0 ) {
// here be dragons
console.log(roomlist);
socket.emit('roomList', roomlist);
}
});
} else --count;
});
});
}

Looks like a job for async.map:
function roomList(socket){
var rooms = getRooms(), p = /pChannel_/;
redis.select(7, function(err, res) {
async.map(rooms, function(room, callback) {
if (room === '' || ! p.test(room))
return callback(null, null);
var key = 'channel:' + room;
var c = io.sockets.manager.rooms[room];
redis.hgetall(key, function (err, reply) {
if (err)
callback(err); // propagate Redis errors to final callback, don't know
// if you want that or not; use 'callback(null)' if not.
else
if (reply)
callback(err, Array(reply.name, c.length, reply.icon) );
else
callback(err, null);
});
}, function(err, roomlist) {
if (err)
// handle Redis errors...
// filter 'null' entries from roomlist
roomlist = roomlist.filter(function(room) { return room !== null });
console.log(roomlist);
socket.emit('roomList', roomlist);
});
});
}
(untested)

If you just want to wait for the room list to be fully built before emitting the response (as seems highly reasonable), and assuming Q to be available, then you should just need a few additional lines of Q magic plus a closure-forming wrapper around the inner code to maintain a reliable reference to a Q deferred at each pass of the for loop.
function roomList(socket) {
redis.select(7, function(err, res) {
var list = [],
rooms = getRooms(),
p = /pChannel_/,
promises = [];
for(var k in rooms) {
if(rooms[k] != '' && p.test(rooms[k])) {
(function(dfrd) {
promises.push(dfrd.promise);
var key = 'channel:' + rooms[k];
redis.hgetall(key, function(err, reply) {
if(reply) {
var c = io.sockets.manager.rooms[rooms[k]];
list.push( [reply['name'], c.length, reply['icon']] );
}
else {
console.log('nothing found');
}
dfrd.resolve();
});
})(Q.defer());
}
}
Q.all(promises).then(function() {
console.log(list);
socket.emit('roomList', list);
});
});
}

Related

Node.js + socket.io + MySQL correction of syntax

Considering that my server.js looks almost like this. Just send you the relevant part. I did not receive anything from the query, I do have data in the database, and "sendNotification" is triggered by the jQuery function in the client. Everything works and since var notis = []; returns an empty value and is what is shows as response. I know I have to debug SQL and that's what I'm going to do but anyway want to be sure of this other things. So my questions are:
1) Is a right syntax for node.js, considering this async behavior? (which I still don't understand )
2) The query always should be inside of the "io.sockets.on('connection')" part?
connection = mysql.createConnection({
host: 'localhost',
user: '',
password: "",
database: 'table' //put your database name
}),
...
connection.connect(function(err) {
// connected! (unless `err` is set)
console.log(err);
});
…
var sqlquery = function(uID,vs){
var notis = [];
connection.query("SELECT * FROM notification WHERE kid = ? AND v = ? ORDER BY id DESC",[uID,vs])
.on("result", function (data){
return notis.push(data);
});
};
io.sockets.on('connection', function(socket) {
...
socket.on("sendNotification", function(data) {
var roomBName = data.room_name.replace("room-",""),
found = [];
var roomSelected = _.find(rooms, function (room) { return room.id == roomBName });
for (var person in people) {
for (var i = 0, numAttending = roomSelected.peopleAttending.length; i < numAttending; i++) {
if (people[person].name == roomSelected.peopleAttending[i]) {
found.push(person);
}
}
}
for (var i = 0, numFound = found.length; i < numFound; i++) {
**result = sqlquery(9,2);**
io.to(found[i]).emit('notification', result);
};
});
Your sqlquery() function will not accomplish anything useful. Because connection.query() is asynchronous, that means it provides the response sometime LATER after sqlquery() has already finished.
The only way in node.js to use an async result is to actually use it in the callback that provides it. You don't just stuff it into some other variable and expect the result to be there for you in other code. Instead, you use it inside that callback or you call some other function from the callback and pass it the data.
Here's one way, you could change your sqlquery() function:
var sqlquery = function(uID, vs, callback){
connection.query("SELECT * FROM notification WHERE kid = ? AND v = ? ORDER BY id DESC",[uID,vs])
.on("result", function (data){
callback(null, data);
});
// need to add error handling here if the query returns an error
// by calling callback(err)
};
Then, you could use the sqlquery function like this:
found.forEach(function(person, index) {
sqlquery(..., function(err, result) {
if (err) {
// handle an error here
} else {
io.to(person).emit('notification', result);
}
});
});
And, it looks like you probably have similar async issues in other places too like in connection.connect().
In addition to #jfriend00, this could be done with new ES6 feature Promise :
var sqlquery = function(uID, vs){
return new Promise(function(resolve, reject){
connection.query("SELECT * FROM notification WHERE kid = ? AND v = ? ORDER BY id DESC",[uID,vs])
.on("result", function (data){
resolve(data);
});
});
};
Now you can use it like :
found.forEach(function(person, index) {
sqlquery(...)
.then(function(result){
io.to(person).emit('notification', result);
});
});

Trying to make my own RxJs observable

I'm trying to convert an existing API to work with RxJS... fairly new to node, and very new to RxJs, so please bear with me.
I have an existing API (getNextMessage), that either blocks (asynchronously), or returns a new item or error via a node-style (err, val) callback, when the something becomes available.
so it looks something like:
getNextMessage(nodeStyleCompletionCallback);
You could think of getNextMessage like an http request, that completes in the future, when the server responds, but you do need to call getNextMessage again, once a message is received, to keep getting new items from the server.
So, in order to make it into an observable collection, I have to get RxJs to keep calling my getNextMessage function until the subscriber is disposed();
Basically, I'm trying to create my own RxJs observable collection.
The problems are:
I don't know how to make subscriber.dispose() kill the async.forever
I probably shouldn't be using async.forever in the first place
I'm not sure I should be even getting 'completed' for each message - shouldn't that be at the end of a sequence
I'd like to eventually remove the need for using fromNodeCallback, to have a first class RxJS observable
Clearly I'm a little confused.
Would love a bit of help, thanks!
Here is my existing code:
var Rx = require('rx');
var port = require('../lib/port');
var async = require('async');
function observableReceive(portName)
{
var observerCallback;
var listenPort = new port(portName);
var disposed = false;
var asyncReceive = function(asyncCallback)
{
listenPort.getNextMessage(
function(error, json)
{
observerCallback(error, json);
if (!disposed)
setImmediate(asyncCallback);
}
);
}
return function(outerCallback)
{
observerCallback = outerCallback;
async.forever(asyncReceive);
}
}
var receive = Rx.Observable.fromNodeCallback(observableReceive('rxtest'));
var source = receive();
var subscription = source.forEach(
function (json)
{
console.log('receive completed: ' + JSON.stringify(json));
},
function (error) {
console.log("receive failed: " + error.toString());
},
function () {
console.log('Completed');
subscription.dispose();
}
);
So here's probably what I would do.
var Rx = require('Rx');
// This is just for kicks. You have your own getNextMessage to use. ;)
var getNextMessage = (function(){
var i = 1;
return function (callback) {
setTimeout(function () {
if (i > 10) {
callback("lawdy lawd it's ova' ten, ya'll.");
} else {
callback(undefined, i++);
}
}, 5);
};
}());
// This just makes an observable version of getNextMessage.
var nextMessageAsObservable = Rx.Observable.create(function (o) {
getNextMessage(function (err, val) {
if (err) {
o.onError(err);
} else {
o.onNext(val);
o.onCompleted();
}
});
});
// This repeats the call to getNextMessage as many times (11) as you want.
// "take" will cancel the subscription after receiving 11 items.
nextMessageAsObservable
.repeat()
.take(11)
.subscribe(
function (x) { console.log('next', x); },
function (err) { console.log('error', err); },
function () { console.log('done'); }
);
I realize this is over a year old, but I think a better solution for this would be to make use of recursive scheduling instead:
Rx.Observable.forever = function(next, scheduler) {
scheduler = scheduler || Rx.Scheduler.default,
//Internally wrap the the callback into an observable
next = Rx.Observable.fromNodeCallback(next);
return Rx.Observable.create(function(observer) {
var disposable = new Rx.SingleAssignmentDisposable(),
hasState = false;
disposable.setDisposable(scheduler.scheduleRecursiveWithState(null,
function(state, self) {
hasState && observer.onNext(state);
hasState = false;
next().subscribe(function(x){
hasState = true;
self(x);
}, observer.onError.bind(observer));
}));
return disposable;
});
};
The idea here is that you can schedule new items once the previous one has completed. You call next() which invokes the passed in method and when it returns a value, you schedule the next item for invocation.
You can then use it like so:
Rx.Observable.forever(getNextMessage)
.take(11)
.subscribe(function(message) {
console.log(message);
});
See a working example here

Dealing with socket.io async get/set calls

I'm trying to interrogate if any of the clients in a room have a particular property associated with them. The async nature of the socket.io get method is causing me problems. I've seen the async library, which looks like it might be what I need, but I'm having difficulties visualising how to apply that to this situation.
Here is how I'd like the function to work, assuming the get wasn't async;
/**
*
**/
socket.on('disconnect', function(data) {
socket.get('room', function(err, room) {
if(!roomHasProperty(room)) {
io.sockets.in(room).emit('status', { message: 'property-disconnect' });
}
});
});
/**
*
**/
var roomClients = function(room) {
var _clients = io.sockets.clients(room);
return _clients;
}
/**
*
**/
var roomHasProperty = function(room) {
// get a list of clients in the room
var _clients = roomClients(room);
// build up an array of tasks to be completed
var tasks = [];
// loop through each socket in the room
for(key in _clients) {
var _socket = _clients[key];
// grab the type from the sockets data store and check for a control type
_socket.get('type', function (err, type) {
// ah crap, you already went ahead without me!?
if(type == 'property') {
// found a the property type we were looking for
return true;
}
});
}
// didn't find a control type
return false;
}
Is there a better way of doing this?
Have you considered using a promises library? It makes dealing with async functions a lot easier.
If you were to use Q, you could do this: (I'm sorry, i can't check the code right now, but I'm pretty sure it should work almost with no changes)
var roomHasProperty = function(room) {
// Create the deferred object
var deferred = Q.defer();
// get a list of clients in the room
var _clients = roomClients(room);
// array of promises to check
var promises = [];
// This function will be used to ask each client for the property
var checkClientProperty = function (client) {
var deferred = Q.defer();
// grab the type from the sockets data store and check for a control type
client.get('type', function (err, type) {
// ah crap, you already went ahead without me!?
if(type == 'property') {
// found a the property type we were looking for
deferred.resolve(true);
} else {
// property wasn't found
deferred.resolve(false);
}
});
return deferred.promise;
}
// loop through each socket in the room
for(key in _clients) {
promises.push(checkClientProperty(_clients[key]));
}
Q.all(promises).then(function (results) {
deferred.resolve(results.indexOf(true) > -1);
})
// didn't find a control type
return deferred.promise;
}
You can use this like this:
checkClientProperty(client).then(function (result) {
if (result) {
console.dir('the property was found');
} else {
console.dir('the property was not found');
}
});

How to send mongodb data async from inner functions to outside callback function from a for loop?

NEW POST:
Here is the sample of the working async code without a db.
The problem is, if i replace the vars (data1_nodb,...) with the db.collection.find();
function, all needed db vars received at the end and the for() loop ends not
correct. I hope that explains my problem a bit better. OA
var calc = new Array();
function mach1(callback){
error_buy = 0;
// some vars
for(var x_c99 = 0; x_c99 < array_temp_check0.length;x_c99++){
// some vars
calc[x_c99] = new Array();
calc[x_c99][0]= new Array();
calc[x_c99][0][0] = "dummy1";
calc[x_c99][0][1] = "dummy2";
calc[x_c99][0][2] = "dummy3";
calc[x_c99][0][3] = "dummy4";
calc[x_c99][0][4] = "dummy5";
function start_query(callback) {
data1_nodb = "data1";
data2_nodb = "data2";
data3_nodb = "data3";
data4_nodb = "data4";
calc[x_c99][0][0] = data1_nodb;
calc[x_c99][0][1] = data2_nodb;
calc[x_c99][0][2] = data3_nodb;
callback(data1_nodb,data2_nodb,etc..);
}
start_query(function() {
console.log("start_query OK!");
function start_query2(callback) {
data4_nodb = "data5";
data5_nodb = "data6";
data6_nodb = "data7";
calc[x_c99][0][3] = data4_nodb;
calc[x_c99][0][4] = data5_nodb;
callback(data5_nodb,data6_nodb,etc..);
}
start_query2(function() {
console.log("start_query2 OK!");
function start_query3(callback) {
for(...){
// do something
}
callback(vars...);
}
start_query3(function() {
console.log("start_query3 OK!");
});
});
});
}
callback(calc);
};
function mach2(callback){
mach1(function() {
console.log("mach1 OK!");
for(...){
// do something
}
});
callback(calc,error_buy);
};
mach2(function() {
console.log("mach2 OK 2!");
});
OLD POST:
i try to read data from the mongodb and send them back with a callback to the next
function, that needs the infos from the db to proceed.
Without the mongodb read functions it works perfect but now i dont know how
i can send the db vars out of the two inner functions to the first callback function.
Hope someone can help me...
Thanks
var error = 0; var var1 = "yessir";
function start_query(callback) {
var db_name = "db1";
db[db_name].find({name:var1},{data1:1, data2:1, data3:1, data4:1}, function(err, data_catch,callback) {
if( err || !data_catch ) {
console.log("Problem finding data_catch:" + err);
} else {
data_catch.forEach( function(data_catch_finder,callback) {
data1_db = data_catch_finder.data1;
data2_db = data_catch_finder.data2;
data3_db = data_catch_finder.data3;
data4_db = data_catch_finder.data4;
if(data1_db == "" || data2_db == "" || data3_db == "" || data4_db == ""){error = 1; console.log("Error: data_catch_finder");}
callback(data1_db, data2_db, data3_db, data4_db, error);
});
}
});
callback(data1, data2, data3, data4, error);
}
//########################################################################
start_query(function() {
function start_query2(callback) {
console.log("DATA1 from callback:" + data1_db);
console.log("DATA2 from callback:" + data2_db);
console.log("DATA3 from callback:" + data3_db);
console.log("DATA4 from callback:" + data4_db);
var var_no_db = "testing";
//do something else and callback
callback(var_no_db);
}
start_query2(function() {
console.log("Var from callback start_query2:" + var_no_db);
console.log("The end");
});
});
your callback signature are issuing callback as a parameter.
As far as I can understand your code, you need to keep reference of the first callback, the one you receive here: function start_query(callback).
In every callback function you made the mistake to bind the variable name callback to the parameter from the mongo driver (a simple undefined i think).
You can fix it removing every reference of callback from the signature of your inner functions.
a simple example:
function async (cb) {
// params: Error, data
cb(null, 'moo');
}
function foo(callback) {
async(function(err, data, callback){
console.log(callback); // undefined
});
console.log(callback); // Moo
}
foo('Moo');
Take a look at Eloquent Javascript to better understand the JS context switching;
edit
The only way to wait the results of an async function is recall the first callback inside the last nested callback.
function ugly_nested (callback) {
dbquery('...', function(err, data_01) {
if (!! err) return callback(err);
dbquery('...', function(err, data_02) {
if (!! err) return callback(err);
dbquery('...', function(err, data_03) {
if (!! err) return callback(err);
callback(null, data_01, data_02, data_03);
});
});
});
}
ugly_nested(function(err, data01, data02, data03) {
if (!! err) throw err;
manage_data(data01, data02, data03);
});
The FOR loop is synchronous, but, the database calls are asynchronous, so, the for loop will end before the database returns his results. If you really need that for loop you can try out one of the nice flow control libraries out there

nested loops asynchronously in Node.js, next loop must start only after one gets completed

Check below algorithm...
users = getAllUsers();
for(i=0;i<users.length;i++)
{
contacts = getContactsOfUser(users[i].userId);
contactslength = contacts.length;
for(j=o;j<contactsLength;j++)
{
phones = getPhonesOfContacts(contacts[j].contactId);
contacts[j].phones = phones;
}
users[i].contacts = contacts;
}
return users;
I want to develop such same logic using node.js.
I have tried using async with foreach and concat and foreachseries functions. But all fail in the second level.
While pointer is getting contacts of one user, a value of i increases and the process is getting started for next users.
It is not waiting for the process of getting contacts & phones to complete for one user. and only after that starting the next user. I want to achieve this.
Actually, I want to get the users to object with proper
Means all the sequences are getting ruined, can anyone give me general idea how can I achieve such a series process. I am open to change my algorithm also.
In node.js you need to use asynchronous way. Your code should look something like:
var processUsesrs = function(callback) {
getAllUsers(function(err, users) {
async.forEach(users, function(user, callback) {
getContactsOfUser(users.userId, function(err, contacts) {
async.forEach(contacts, function(contact, callback) {
getPhonesOfContacts(contacts.contactId, function(err, phones) {
contact.phones = phones;
callback();
});
}, function(err) {
// All contacts are processed
user.contacts = contacts;
callback();
});
});
}, function(err) {
// All users are processed
// Here the finished result
callback(undefined, users);
});
});
};
processUsers(function(err, users) {
// users here
});
You could try this method without using async:
function getAllUserContacts(users, callback){
var index = 0;
var results = [];
var getUserContacts = function(){
getContactsOfUser(users[index].userId, function(contacts){
var index2 = 0;
var getContactsPhones = function(){
getPhonesOfContacts(contacts[index2].contactId, function(phones){
contacts[index2].phones = phones;
if(index2 === (contacts.length - 1)){
users[index].contacts = contacts;
if(index === (users.length - 1)){
callback(users)
} else {
index++;
getUserContacts();
}
}else{
index2++;
getContactsPhones();
}
});
}
getContactsPhones();
});
}
getUserContacts();
}
//calling the function
getAllUsers(function(users){
getAllUsersWithTheirContacts(users, function(usersWithContacts){
console.log(usersWithContacts);
})
})
//Asynchronous nested loop
async.eachSeries(allContact,function(item, cb){
async.eachSeries(item,function(secondItem,secondCb){
console.log(secondItem);
return secondCb();
}
return cb();
},function(){
console.log('after all process message');
});

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