We Keep Coding

firebase transaction and if-then-else behaviour

I have some changes in my requirements:
Not only Create/Request/Cancel an entire Offer but do some actions on Offer's details:
Here is an offer in the activeOffers list:
activeOffers
-LKohyZ58cnzn0vCnt9p
details
direction: "city"
seatsCount: 2
timeToGo: 5
uid: "-ABSIFJ0vCnt9p8387a" ---- offering user
A user should be able to 'ask for seats' and if it's successful the Offer record should look like this:
activeOffers
-LKohyZ58cnzn0vCnt9p
details
direction: "city"
seatsCount: 1 ----- reduced count
timeToGo: 5
uid: "-ABSIFJ0vCnt9p8387a"
deals
-GHFFJ0vCnt9p8345b ----- the userId of asking user
seatsCount: 1
status: "asked"
But I have 3 problems after executing the source shown below:
(as shown above offer has 2 seats and a user asks for 1 seat)
After execution in my log I have BOTH "Reducing seats count by 1" and "Not enought seats"... i.e: the 'then' and 'else' part of 'if-then-else' :o
function result is [] - i.e. no deal created.
I'm not sure how to do the TODO: part - to add child (the new deal object) under dealsRef using asking userId as KEY because I think I don't need an autogenerated key here.
input data has the following structure:
data
"uid": "-GHFFJ0vCnt9p8345b", ----- the userId of asking user
"id": "-LKohyZ58cnzn0vCnt9p", ----- the id of offer
"details":
"seatsCount": 1
And here is my code:
dealSeats = function(data) {
const TAG = '[dealSeats]: ';
var details = data.details;
var info = data.info;
var entryRef = db.ref('activeOffers/' + data.id);
var entryDetailsRef = entryRef.child('details');
var seatsCountRef = entryDetailsRef.child('seatsCount');
var success = false;
return seatsCountRef.transaction((current)=>{
var value = current;
if (value >= details.seatsCount) {
success = true;
value = value - details.seatsCount;
console.log(TAG + 'Reducing seats count by ' + details.seatsCount);
} else {
console.log(TAG + 'Not enought seats');
}
return value;
})
.then(()=>{
var deal = [];
if (success) {
console.log(TAG + 'Succes');
deal.seatsCount = details.seatsCount;
deal.status = 'asked';
// TODO: here should add the new deal to dealsRef
return deal;
} else {
console.log(TAG + 'Failure');
return deal;
}
})
}
And as you can see - I'm not sure what is the right way to check if transaction is succeeded...

The reference documentation for DatabaseReference.transaction says:
... until your write succeeds without conflict or you abort the transaction by not returning a value from your update function.
So the way to abort the transaction is by not returning any value from your update function. That means the entire first block can be simplified to:
seatsCountRef.transaction((current)=>{
if (current >= details.seatsCount) {
return value - details.seatsCount;
}
})
Now it either returns the new value, or it returns nothing. The latter will then make Firebase abort the transaction.
To detect the final output of a transaction, I find it easiest to work with a completion callback (instead of a Promise), since it gives you all parameters in one call:
seatsCountRef.transaction((current)=>{
if (current >= details.seatsCount) {
return value - details.seatsCount;
}
}, function(error, committed, snapshot) {
if (error) {
console.log('Transaction failed abnormally!', error);
} else if (!committed) {
console.log('We aborted the transaction, because there are not enough seats.');
} else {
console.log('Seat count updated');
}
})
The most common cause for that first error condition will be that the transaction had to be retried too frequently, meaning that too many users are trying to claim seats at the same time. A typical solution here would be to back off, i.e. have the client retry later.

Dynamically adjust object names based on parameter

I'm running a script on an apache webserver on a linux box. Based on the parameter I want to change the name of variable(or set it)
The idea is that humDev(lines 11 and 14) is named humDev21 for example. Where devId is the number 21 in this example.
My script looks like this:
function getHumDev(devId){
$.ajax({
async: false,
url: "/url" + devId,
success: function(result) {
var array = result["Device_Num_" + devId].states;
function objectFindByKey(array, key, value) {
for (var i = 0; i < array.length; i++) {
if (array[i][key] === value) {
humDev = array[i].value;
}
}
return humDev;
};
objectFindByKey(array, 'service', 'some');
}
});
};
If Im looking in the wrong direction, please do let me know. Maybe its bad practice what Im trying. The reason I want to have the object a unique name is because this function is called several times by another function, based on the content of an array. But when I have the humDev object named without the number suffix to make it unique, the content of the object is getting mixed up between the different calls.

I may be off base but I am making some assumptions based on what I understand of what you are trying to do.
First, you need to understand how to do file I/O in node.js. So lets start there:
var pathToFile, //set with file path string
fs = require('fs'), //require the file i/o module API
bunchOfHumDevs = {},
fileContents; //we'll cache those here for repeated use
fs.readFile(pathToFile, function(err, result) {
if (err) {
throw new Error(); //or however you want to handle errors
} else {
fileContents = JSON.parse(result); //assumes data stored as JSON
}
});
function getHumDev(devId) {
//first make sure we have fileContents, if not try again in 500ms
if (!fileContents) {
setTimeout(function() {
getHumDev(devId);
}, 500);
} else {
var array = fileContents["Device_Num_" + devId].states,
i = array.length,
//if 'service' and 'some' are variable, make them params of
//getHumDev()
while (i--) {
if (array[i]['service'] === 'some') {
//store uniquely named humDev entry
bunchOfHumDevs['humDev' + devId.toString()] = array[i].value;
break; //exit loop once a match is found
}
}
}
return null;
}
getHumDev(21);
assuming a match is found for the devId 21, bunchOfHumdevs will now have a property 'humDev21' that is the object (value?) in question. Also, the fileContents are now cached in the program so you don't have to reopen it every time you call the function.

Batch requests in Node.js

My program is communicating with a web service that only accepts ~10 requests per second. From time to time, my program sends 100+ concurrent requests to the web service, causing my program to crash.
How do I limit concurrent requests in Node.js to 5 per second? Im using the request library.
// IF EVENT AND SENDER
if(data.sender[0].events && data.sender[0].events.length > 0) {
// FIND ALL EVENTS
for(var i = 0; i < data.sender[0].events.length; i++) {
// IF TYPE IS "ADDED"
if(data.sender[0].events[i].type == "added") {
switch (data.sender[0].events[i].link.rel) {
case "contact" :
batch("added", data.sender[0].events[i].link.href);
//_initContacts(data.sender[0].events[i].link.href);
break;
}
// IF TYPE IS "UPDATED"
} else if(data.sender[0].events[i].type == "updated") {
switch (data.sender[0].events[i].link.rel){
case "contactPresence" :
batch("updated", data.sender[0].events[i].link.href);
//_getContactPresence(data.sender[0].events[i].link.href);
break;
case "contactNote" :
batch("updated", data.sender[0].events[i].link.href);
// _getContactNote(data.sender[0].events[i].link.href);
break;
case "contactLocation" :
batch("updated", data.sender[0].events[i].link.href);
// _getContactLocation(data.sender[0].events[i].link.href);
break;
case "presenceSubscription" :
batch("updated", data.sender[0].events[i].link.href);
// _extendPresenceSubscription(data.sender[0].events[i].link.href);
break;
}
}
};
And then the homegrown batch method:
var updated = [];
var added = [];
var batch = function(type, url){
console.log("batch called");
if (type === "added"){
console.log("Added batched");
added.push(url);
if (added.length > 5) {
setTimeout(added.forEach(function(req){
_initContacts(req);
}), 2000);
added = [];
}
}
else if (type === "updated"){
console.log("Updated batched");
updated.push(url);
console.log("Updated length is : ", updated.length);
if (updated.length > 5){
console.log("Over 5 updated events");
updated.forEach(function(req){
setTimeout(_getContactLocation(req), 2000);
});
updated = [];
}
}
};
And an example of the actual request:
var _getContactLocation = function(url){
r.get(baseUrl + url,
{ "strictSSL" : false, "headers" : { "Authorization" : "Bearer " + accessToken }},
function(err, res, body){
if(err)
console.log(err);
else {
var data = JSON.parse(body);
self.emit("data.contact", data);
}
}
);
};

Using the async library, the mapLimit function does exactly what you want. I can't provide an example for your specific use case as you did not provide any code.
From the readme:
mapLimit(arr, limit, iterator, callback)
The same as map only no more than "limit" iterators will be simultaneously
running at any time.
Note that the items are not processed in batches, so there is no guarantee that
the first "limit" iterator functions will complete before any others are
started.
Arguments
arr - An array to iterate over.
limit - The maximum number of iterators to run at any time.
iterator(item, callback) - A function to apply to each item in the array.
The iterator is passed a callback(err, transformed) which must be called once
it has completed with an error (which can be null) and a transformed item.
callback(err, results) - A callback which is called after all the iterator
functions have finished, or an error has occurred. Results is an array of the
transformed items from the original array.
Example
async.mapLimit(['file1','file2','file3'], 1, fs.stat, function(err, results){
// results is now an array of stats for each file
});
EDIT: Now that you provided code, I see that your use is a bit different from what I assumed. The async library is more useful when you know all the tasks to run up front. I don't know of a library off hand that will easily solve this for you. The above note is likely still relevant to people searching this topic so I'll leave it in.
Sorry, I don't have time to restructure your code, but this is an (un-tested) example of a function that makes an asynchronous request while self-throttling itself to 5 requests per second. I would highly recommend working off of this to come up with a more general solution that fits your code base.
var throttledRequest = (function () {
var queue = [], running = 0;
function sendPossibleRequests() {
var url;
while (queue.length > 0 && running < 5) {
url = queue.shift();
running++;
r.get(url, { /* YOUR OPTIONS HERE*/ }, function (err, res, body) {
running--;
sendPossibleRequests();
if(err)
console.log(err);
else {
var data = JSON.parse(body);
self.emit("data.contact", data);
}
});
}
}
return function (url) {
queue.push(url);
sendPossibleRequests();
};
})();
Basically, you keep a queue of all the data to be asynchronously processed (such as urls to be requested) and then after each callback (from a request) you try to launch off as many remaining requests as possible.

This is precisely what node's Agent class is designed to address. Have you done something silly like require('http').globalAgent.maxSockets = Number.MAX_VALUE or passed agent: false as a request option?
With Node's default behavior, your program will not send more than 5 concurrent requests at a time. Additionally, the Agent provides optimizations that a simple queue cannot (namely HTTP keepalives).
If you try to make many requests (for example, issue 100 requests from a loop), the first 5 will begin and the Agent will queue the remaining 95. As requests complete, it starts the next.
What you probably want to do is create an Agent for your web service requests, and pass it in to every call to request (rather than mixing requests in with the global agent).
var http=require('http'), svcAgent = http.Agent();
request({ ... , agent: svcAgent });

Casper JS waitForResource with a restful API

We are having a little problem with a functional test with casper.js.
We request the same resource twice, first with the GET and then with POST method.
Now when waiting for the second resource (POST) it matches the first resource and directly goes to the "then" function.
We would like to be able to check for the HTTP method in the "test" function, that way we can identify the resource properly. For now we use the status code (res.status), but that doesn't solve our problem fully, we really need the http method.
// create new email
this.click(xPath('//div[#id="tab-content"]//a[#class="button create"]'));
// GET
this.waitForResource('/some/resource',
function then() {
this.test.assertExists(xPath('//form[#id="email_edit_form"]'), 'Email edit form is there');
this.fill('form#email_edit_form', {
'email_entity[email]': 'test.bruce#im.com',
'email_entity[isMain]': 1
}, true);
// POST
this.waitForResource(
function test(res) {
return res.url.search('/some/resource') !== -1 && res.status === 201;
},
function then() {
this.test.assert(true, 'Email creation worked.');
},
function timeout() {
this.test.fail('Email creation did not work.');
}
);
},
function timeout() {
this.test.fail('Email adress creation form has not been loaded');
});
Or maybe there is a better way to test this scenario? Although since this is a functional test we need to keep all those steps in one test.

You can try to alter the form action url to add some query string, therefore generating a new resource appended to the stack. Could be done this way:
casper.thenEvaluate(function() {
var form = __utils__.findOne('#email_edit_form');
form.setAttribute('action', form.getAttribute('action') + '?plop');
});
That's a hack though, and functional testing should never be achieved that way. Let's hope more information will be added to the response objects in the future.

The res parameter that is passed to the test function has an ID. I created a helper that tests against this ID and blacklists it, so the same resource won't get accepted a second time.
var blackListedResourceIds = [],
testUniqueResource = function (resourceUrl, statusCode) {
return function (res) {
// check if resource was already loaded
var resourceFound = res.url.search(resourceUrl) !== -1;
// check statuscode
if (statusCode !== undefined) {
resourceFound = resourceFound && res.status === statusCode;
}
// check blacklisting
if (!resourceFound || blackListedResourceIds[res.id] !== undefined) {
return false;
} else {
blackListedResourceIds[res.id] = true;
return true;
}
};
};

How to extract partial JSON from API response?

Load when the browser is open
Thats my previous question related to this topic.
My problem is that the server api i use has added a new item to the list and as i stated in the previous question im not very skilled with API's or jQuery, therefore i would like to know what can you recomend me to read about this and also pratical solutions. I need to make it so the field that the js uses is only {"name":"Arthas","slug":"arthas","build":"12340","status":1} and not the rest.
Many thanks in advance.
This is the api -> http://api.neverendless-wow.com/server-status
{"servers":[{"name":"Arthas","slug":"arthas","build":"12340","status":1},{"name":"Deathwing","slug":"deathwing","build":"13623","status":1}],"alerts":[]}
This is my current js
function checkStatus()
{
jQuery.getJSON("http://api.neverendless-wow.com/server-status",function(data){
if (data.status == '1') {jQuery('#ServStat').addClass('online').removeClass('offline').attr('label','Online');}
else {jQuery('#ServStat').addClass('offline').removeClass('online').attr('label','Offline');}});
}
checkStatus();
{
setInterval(changeState, 300000)
}

You need to use data as array (data[0]) and hence your code will be as follows:
function checkStatus()
{
jQuery.getJSON("http://api.neverendless-wow.com/server-status",function(data){
if (data.servers[0].status == '1') {
jQuery('#ServStat').addClass('online').removeClass('offline').attr('label','Online');
}
else {
jQuery('#ServStat').addClass('offline').removeClass('online').attr('label','Offline');
}
});
}
checkStatus();
{
setInterval(changeState, 300000)
}

I would probably go with something like this:
// check server status
function checkStatus()
{
$.getJSON(server_url, function(data) {
// reset
var mode = "Offline";
$('.status').removeClass('online').addClass('offline');
// is available?
if (data !== null && data.servers !== null && data.servers[0].status === 1) {
mode = "Online";
$('.status').removeClass('offline').addClass('online');
}
// Extract data from received JSON string is exists
extractData(data);
// set needed attributes
$('.status')
.attr('label', mode)
.text('Servers are ' + mode);
});
}
Live demo available on JsBin