Sony Arouje

a programmer's log

Archive for the ‘JavaScript’ Category

Slack App to track our expenses hosted in a Raspberry Pi

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At 4Mans Land we keep struggling to track our expenses. We normally note the expenses in Whatsapp and later move to a shared excel sheet. But this is always have difficulties, there will be lot of noises in the whatsapp with ongoing discussions. We also use slack for discussions, so I decided to integrate an expense app and evaluated some. Most of them are paid and don’t want to pay for an app at this stage. One night decided to write an app for slack and by morning finished the basic app that can store expenses in a mongodb. This whole experiment started as a fun to play with some thing new and also understand the slack api.

Wrote the server in nodejs and choose mongo db for persistence. For testing the slack integration, I used ngrok to create a local tunnel. also evaluated which is a free version, but very unstable. ngrok is good but we have to pay $5 per month for license.  Started evaluating other alternatives to host my server, heroku was another alternative and used it several times earlier. At the moment we wanted to spend less for hosting and infrastructure. At last decided to host the server at my home, I have a really good stable internet connection with more than 80mbps speed and a Gigabit router. Added a port forwarding at my router,  expected to access the port immediately but to my surprise it’s not working. Done port forwarding so many times earlier and could access stuffs inside my network without any issues, my ISP was different that time. Then called up my ISP support, they informed me that without a static ip I wont be able to do port forwarding, for static IP I have to pay a very minimal fee and is life long unless I switch the provider. Paid the amount and in 2 days got my static IP and could do port forwarding successfully. Also set up dynamic dns at to give a good name to my IP. With all these settings done, changed the url in slack app and used the one I setup at Run the nodejs server at my dev machine and fired a command from slack app, viola received the command to the server running in my laptop. The server is ready and is running in my laptop, but required a system which could run 24/7. The cheap option came to my mind was to host the nodejs server in one of the Raspberrypi lying in my table, one night I decided to setup the pi with the latest Raspbian stretch.

Setting up the Raspberry pi

Expected to finish the whole setup in less than an hour, as did this several times earlier but not that day. After installing the stretch, apt-get update started throwing hash sum error, reinstalled the os couple of times. Same error again and again. This error sent me for a wild goose chase, reading one forum after another and tried all the suggestions but nothing changed. At last came across this stackoverflow post which fixed the issue and could update the os, phew.

Next installing the nodejs, used nodejs version maintained here and issue the ubuntu command, for e.g. to install nodejs 10 issue the below command from your raspberry pi

curl sL | sudo -E bash – sudo aptget install y nodejs

Next task is installing Mongodb, apt-get install mongodb installed an earlier version of mongodb and is not suitable for the mongoose orm which I am using in the code, either I have to use an older version of mongoose or try to find a way to install a new version of Mongodb. I choose the later and try hunting for some clues to install some newer version of mongodb. At the end, come accross this post, which has all the details of installing mongodb in Rpi jessie, which is good enough in stretch as well, also he provided a link for stretch mongo binaries. Followed the instructions and at the end mongodb started running in my machine.

When I try to connect from Compass to rpi’s mongodb instance, it’s not getting connected. Reading through some docs and forums realized that I have to comment bind_ip in /etc/mongodb.conf, commented out that config and able to connect from compass.

Before going to bed at 2am, copied the nodejs code to rpi, did some testing and all went well. Could post expenses from slack to the service running in my pi. Went to bed with peace of mind.

What this app does?

The main focus of this app is to capture the expense, for now it uses slack command to forward text to the service. Initially created a strict pattern to record expense for e.g.

/expense spent 4000 INR on Jill to fetch a pail of water by Jack

Here spent should be first word followed by amount, after ‘on’ specify the description and after ‘by’ specified who paid the amount. The nodejs service will parse them and place them in separate fields in mongodb collection. Then to query the expense, some thing like

/expense query date today

/expense query date 05/12/2018 – 05/14/2018

So here ‘spent’ and ‘query’ is a keyword, based on this keyword different handling logics will kicks in and complete the task.

I felt the syntax is more restrictive, started analyzing options to process the sentence more naturally. I come across natural, a NLP library for nodejs. Using natural’s BayesClassifier trained the system to categorize the input text and derive the right keyword, which again calls the different logic and get the task done. After the classification training, the system can take inputs like

/expense Jack paid 4000 by Card for ‘Jill to fetch a pail of water’ on 05/16/2018

The above code will classified as spent, then added some code to extract relevant part from the text. Not pure NLP approach, any thing inside single quotes will be considered as expense. Any date in the text is considered as the payment date and so on. I am learning NLP, in future I might achieve a better translation of text.

Querying command is modified as shown below

/expense today

/expense between 05/12/2018 – 05/14/2018

Can also query and return expenses in csv format

/expense today csv  will return the expense in comma seperated format.

Slack output


After each expense created successfully, it returns the expense with the ID and the actual text we passed to the expense command. For e.g to create first expense passed the text like

/expense Jack paid 4000 to ‘Jill to fetch a pail of water’

Here is the output for querying todays expense, issue a command like

/expense today



In csv format (/expense today csv)


We can also delete an expense, only the expense you created can be deleted.

/expense delete today: delete all the expense you entered today

/expense delete 116: delete the expense with id 116

Had a great fun during this experiment and learned few things.

Happy coding…


Written by Sony Arouje

May 18, 2018 at 5:17 pm

react, redux and cycle – Introduction

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Last couple of months we were working mostly in react js to develop a flexible platform for one of the product we are working. I am planning to make a couple of post to explain how to start developing in react with redux and cycle. To setup my dev environment, I used the react boilerplate created by my friend Sendhil. This is a basic template to jumbstart react js development with linting.

I am not going in depth of redux or redux-cycle, it’s just an attempt to help setup the initial phase of the development. If you are not familiar with redux or why we need redux, better learn it from the creator.

Let’s use the template and incrementally add more features to it. I created a new github repository with some initial code to start with.

Below are the new npm dependencies added to package.json

  • react-redux: "^5.0.4",
  • redux: "^3.6.0",
  • @cycle/http: "^13.3.0",
  • @cycle/run: "^3.1.0",
  • @cycle/time: "^0.8.0",
  • redux-cycles: "^0.4.1",
  • xstream: "^10.9.0",
  • prop-types: "^15.5.10"

For any redux application we need to setup a store. I created a store as well, see the code below.

import { applyMiddleware, createStore, compose } from 'redux'; import { createCycleMiddleware } from 'redux-cycles'; import { run } from '@cycle/run'; import { makeHTTPDriver } from '@cycle/http'; import { timeDriver } from '@cycle/time'; import logger from 'redux-logger'; // combined all the reducers in the application import reducers from './reducers'; // combined all the cycles in the application import cycles from './cycles'; //create cycle middleware to attach to redux store. const cycleMiddleware = createCycleMiddleware(); const { makeActionDriver, makeStateDriver } = cycleMiddleware; //we might use multiple middleware, here we used a logger //and cycle. We can add more middleware by adding them to //the below array. const middleWare = [ logger, cycleMiddleware, ]; const initState = {}; // more about compose here let composeEnhancers = compose; // adding redux dev tool to visualize the store state. // should be enabled only in development. if (process.env.NODE_ENV !== 'production') { const composeWithDevToolsExtension = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__; if (typeof composeWithDevToolsExtension === 'function') { composeEnhancers = composeWithDevToolsExtension; } } const store = createStore( reducers, // all the available reducers combined initState, // initial state of the reducers composeEnhancers( // adding store enchancers applyMiddleware(...middleWare), // attaching the middleware ), ); // calling cycle's run() we are activating the cycles that we created // here all the different cycles are combined to one. run(cycles, { ACTION: makeActionDriver(), STATE: makeStateDriver(), Time: timeDriver, HTTP: makeHTTPDriver(), }); export default store;


Added some inline comments to the code and hopefully it’s pretty self explanatory. Once we have the store created, we need to pass down the store to other components, so that they can access state or dispatch actions.

Let’s edit index.jsx and add the below code.

import React from 'react'; import { render } from 'react-dom'; import { Provider } from 'react-redux'; import store from './store/create-store'; import App from './App'; render( <Provider store={store}> <App /> </Provider> , document.getElementById('root'));


Great, we created a basic react app with redux. In next post I will cover how to create reducer and handle side effects using redux-cycle.


Happy coding…

Written by Sony Arouje

September 22, 2017 at 6:32 pm

Posted in JavaScript, React

Tagged with , ,

RF Communication using nrf24L01 and Nodejs addon

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Recently I started experimenting with radio communication with low cost nrf24L01 modules. These modules are very cheap compare to XBee modules which I used earlier. With these nrf24 modules we could enable wireless communication between Arduinos and Raspberry pi very effectively and economically. For my experiment I used two nrf24 modules, one connected to an Arduino Uno and another to a Raspberry pi 1.  Here is the pin connection details

Seq NRF24L01 RPi Arduino Uno
1 GND 25 (GND) GND
2 VCC 17 (3.3v) 3.3v
3 CE 15 7
4 CSN 24 8
5 SCK 23 13
6 MOSI 19 11
7 MISO 21 12


For testing the communication, I used the RF24Network library, which is very good and has good documentation. Also it comes with e.g for both Arduino and RPi. So I didn’t write any single code just used the e.g and able to see the communication working, initially I had some troubles and at the end every thing worked well, I can see the data coming from Arduino in RPi. 

My intention is to use these modules in RPi and write code in nodejs. Unfortunately there is no nodejs support for this library. So last night I decided to write a nodejs addon for this C/C++ library. I didn’t had any experience in writing a nodejs addon, I spend an hour understanding the Nan and creating very simple addons. Then I started writing the addon for RF24Network, this task was very hard than trying with simple hello world addons.

Node-gyp was keep on failing when it tries to compile the RFNetwork modules. In my searches I realized that node-gyp uses make utility and I need to add the C/C++ files of this library. At the end I could compile the node addon. See the binding.gyp file

{ "targets": [ { "target_name": "nrf24Node", "sources": [ "", "RF24/RF24.cpp", "RF24/utility/RPi/spi.cpp", "RF24/utility/RPi/bcm2835.c", "RF24/utility/RPi/interrupt.cpp", "RF24Network/RF24Network.cpp", "RF24Network/Sync.cpp" ], "include_dirs": [ "<!(node -e \"require('nan')\")", "RF24Network", "RF24" ], "link_settings": { "libraries": [ "-RF24", "-RFNetwork" ] } } ] }


I should say, I am just a beginner in node-gyp and this binding.gyp might need some improvements. Anyway with this gyp file, the compilation succeeded.

Next is to create the addon file. Here I had to learn more about the data types of Nan and Callbacks. I started simple functions to begin with and compile again, then moved on to next. I took more time in understanding callbacks which allows the addon to call javascript callback functions. Also spend a lot of time in understanding threading and creating a module to continuous listening of incoming messages and trigger the callback function, so that nodejs can process those incoming messages. I use libuv for threading, it seems more easy to understand than Async worker modules in Nan.

That whole night I spend learning and writing and refactoring the addon, I finished the module by early morning. By that time I could write a nodejs app and could listen to incoming messages.

Here is the sample code in node js to listen and acknowledge the message back to the sender.

var rf24 = require('./build/Release/nrf24Node.node'); rf24.begin(90,00); rf24.printDetails(); rf24.write(1,"Ack"); rf24.readAsync(function(from, data){ console.log(from); console.log(data); rf24.write(from,"Ack"); }); process.on('SIGINT', exitHandler); function exitHandler() { process.exit(); rf24.close(); }


Here is the complete addon. The code is uploaded to github, with the steps to compile and use it your own nodejs applications.

#include <nan.h> #include <v8.h> #include <RF24.h> #include <RF24Network.h> #include <iostream> #include <ctime> #include <stdio.h> #include <time.h> #include <string> using namespace Nan; using namespace v8; RF24 radio(RPI_V2_GPIO_P1_15, BCM2835_SPI_CS0, BCM2835_SPI_SPEED_8MHZ); RF24Network network(radio); Nan::Callback *cbPeriodic; uv_async_t* async; struct payload_t { // Structure of our payload char msg[24]; }; struct payload_pi { uint16_t fromNode; char msg[24]; }; //-------------------------------------------------------------------------- //Below functions are just replica of RF24Network functions. //No need to use these functions in you app. NAN_METHOD(BeginRadio) { radio.begin(); } NAN_METHOD(BeginNetwork){ uint16_t channel = info[0]->Uint32Value(); uint16_t thisNode = info[0]->Uint32Value(); network.begin(channel,thisNode); } NAN_METHOD(Update) { network.update(); } NAN_METHOD(Available) { v8::Local<v8::Boolean> status = Nan::New(network.available()); info.GetReturnValue().Set(status); } NAN_METHOD(Read) { payload_t payload; RF24NetworkHeader header;,&payload,sizeof(payload)); info.GetReturnValue().Set(Nan::New(payload.msg).ToLocalChecked()); } //-------------------------------------------------------------------------------- NAN_METHOD(Begin){ if (info.Length() < 2) return Nan::ThrowTypeError("Should pass Channel and Node id"); uint16_t channel = info[0]->Uint32Value(); uint16_t thisNode = info[1]->Uint32Value(); radio.begin(); delay(5); network.begin(channel, thisNode); } NAN_METHOD(Write){ if (info.Length() < 2) return Nan::ThrowTypeError("Should pass Receiver Node Id and Message"); uint16_t otherNode = info[0]->Uint32Value(); v8::String::Utf8Value message(info[1]->ToString()); std::string msg = std::string(*message); payload_t payload; strncpy(payload.msg, msg.c_str(),24); RF24NetworkHeader header(otherNode); bool ok = network.write(header,&payload, sizeof(payload)); info.GetReturnValue().Set(ok); } void keepListen(void *arg) { while(1) { network.update(); while (network.available()) { RF24NetworkHeader header; payload_t payload;,&payload,sizeof(payload)); payload_pi localPayload; localPayload.fromNode = header.from_node; strncpy(localPayload.msg, payload.msg, 24); async->data = (void *) &localPayload; uv_async_send(async); } delay(2000); } } void doCallback(uv_async_t *handle){ payload_pi* p = (struct payload_pi*)handle->data; v8::Handle<v8::Value> argv[2] = { Nan::New(p->fromNode), Nan::New(p->msg).ToLocalChecked() }; cbPeriodic->Call(2, argv); } NAN_METHOD(ReadAsync){ if (info.Length() <= 0) return Nan::ThrowTypeError("Should pass a callback function"); if (info.Length() > 0 && !info[0]->IsFunction()) return Nan::ThrowTypeError("Provided callback must be a function"); cbPeriodic = new Nan::Callback(info[0].As<Function>()); async = (uv_async_t*)malloc(sizeof(uv_async_t)); uv_async_init(uv_default_loop(), async, doCallback); uv_thread_t id; uv_thread_create(&id, keepListen, NULL); uv_run(uv_default_loop(), UV_RUN_DEFAULT); } NAN_METHOD(PrintDetails) { radio.printDetails(); } NAN_METHOD(Close){ uv_close((uv_handle_t*) &async, NULL); } NAN_MODULE_INIT(Init){ Nan::Set(target, New<String>("beginRadio").ToLocalChecked(), GetFunction(New<FunctionTemplate>(BeginRadio)).ToLocalChecked()); Nan::Set(target, New<String>("beginNetwork").ToLocalChecked(), GetFunction(New<FunctionTemplate>(BeginNetwork)).ToLocalChecked()); Nan::Set(target, New<String>("update").ToLocalChecked(), GetFunction(New<FunctionTemplate>(Update)).ToLocalChecked()); Nan::Set(target, New<String>("printDetails").ToLocalChecked(), GetFunction(New<FunctionTemplate>(PrintDetails)).ToLocalChecked()); Nan::Set(target, New<String>("available").ToLocalChecked(), GetFunction(New<FunctionTemplate>(Available)).ToLocalChecked()); Nan::Set(target, New<String>("read").ToLocalChecked(), GetFunction(New<FunctionTemplate>(Read)).ToLocalChecked()); Nan::Set(target, New<String>("readAsync").ToLocalChecked(), GetFunction(New<FunctionTemplate>(ReadAsync)).ToLocalChecked()); Nan::Set(target, New<String>("write").ToLocalChecked(), GetFunction(New<FunctionTemplate>(Write)).ToLocalChecked()); Nan::Set(target, New<String>("close").ToLocalChecked(), GetFunction(New<FunctionTemplate>(Close)).ToLocalChecked()); Nan::Set(target, New<String>("begin").ToLocalChecked(), GetFunction(New<FunctionTemplate>(Begin)).ToLocalChecked()); } NODE_MODULE(nrf24Node, Init)

All the credit goes to the developers of RF24 and RF24Network library, I just created an addon for the great library. Along the way I learned a lot and could finish the nodejs addon.


Happy coding…

Written by Sony Arouje

February 5, 2017 at 4:57 pm

Communication between Raspberry Pi and Arduino using XBee

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Recently I was doing some experiments to establish a wireless communication between a Raspberry pi and Arduino. To establish wireless communication I used XBee Pro Series 2 from Digi International. The idea behind this test setup is to test, whether I can control devices like motor or read different sensors remotely.

One of the biggest advantage of using XBee is, you can find a lot of tutorials and libraries for any kind of system and programming languages. For this test app, I used Node js in RPi and C in Arduino.

Test Setup

XBee: I configured two xbee, one as Coordinator and another as Router. Both in API mode 2 (AP =2). I used XCTU to configure both the device. Only reason to choose API 2 is because the Arduino library I used only support API mode 2.

Raspberry pi: connected Coordinator XBee to one of my RPi. You can see more about the connection in one of my earlier post.

Arduino Uno: connected the Router xbee to one of my Arduino. The connection is pretty simple as below.

  • XBee Rx –> Arduino Tx
  • XBee Tx -> Arduino Rx
  • XBee 3.3v-> Arduino 3.3v
  • XBee Gnd –>Arduino Gnd


Raspberry Pi Node js code

Modules used

  • xbee-api: npm install xbee-api
  • serialport: npm install serialport


var util = require('util'); var SerialPort = require('serialport').SerialPort; var xbee_api = require('xbee-api'); var C = xbee_api.constants; var xbeeAPI = new xbee_api.XBeeAPI({ api_mode: 2 }); var serialport = new SerialPort("/dev/ttyAMA0", { baudrate: 9600, parser: xbeeAPI.rawParser() }); var frame_obj = { type: 0x10, id: 0x01, destination64: "0013A200407A25AB", broadcastRadius: 0x00, options: 0x00, data: "MTON" }; serialport.on("open", function () { serialport.write(xbeeAPI.buildFrame(frame_obj)); console.log('Sent to serial port.'); }); // All frames parsed by the XBee will be emitted here xbeeAPI.on("frame_object", function (frame) { console.log(">>", frame); if(!== undefined) console.log('utf8')); });



Arduino Sketch

This sketch uses a XBee library, to add the library, goto Sketch->Include Library->Manage Libraries. From the window search for XBee and install the library. I am using Arduino IDE 1.6.7.

I use SoftwareSerial to establish serial communication with XBee, Pin 2 is Arduino Rx and Pin 3 is Arduino Tx.


#include <Printers.h> #include <XBee.h> #include <SoftwareSerial.h> unsigned long previousMillis = 0; const long interval = 4000; // the interval in mS XBee xbee = XBee(); // XBee's DOUT (TX) is connected to pin 2 (Arduino's Software RX) // XBee's DIN (RX) is connected to pin 3 (Arduino's Software TX) SoftwareSerial soft(2,3);// RX, TX Rx16Response rx16 = Rx16Response(); ZBRxResponse rx = ZBRxResponse(); XBeeAddress64 addr64 = XBeeAddress64(0x0013a200,0x407a25b5); char Buffer[128]; char RecBuffer[200]; void setup() { // put your setup code here, to run once: soft.begin(9600); Serial.begin(9600); xbee.setSerial(soft); } void print8Bits(byte c){ uint8_t nibble = (c >> 4); if (nibble <= 9) Serial.write(nibble + 0x30); else Serial.write(nibble + 0x37); nibble = (uint8_t) (c & 0x0F); if (nibble <= 9) Serial.write(nibble + 0x30); else Serial.write(nibble + 0x37); } void print32Bits(uint32_t dw){ print16Bits(dw >> 16); print16Bits(dw & 0xFFFF); } void print16Bits(uint16_t w){ print8Bits(w >> 8); print8Bits(w & 0x00FF); } void loop() { // put your main code here, to run repeatedly: xbee.readPacket(); if (xbee.getResponse().isAvailable()) { if (xbee.getResponse().getApiId() == ZB_RX_RESPONSE) { xbee.getResponse().getZBRxResponse(rx); if (rx.getOption() == ZB_PACKET_ACKNOWLEDGED) { // the sender got an ACK Serial.println("got ACK"); } else { // we got it (obviously) but sender didn't get an ACK Serial.println("not got ACK"); } Serial.print("Got an rx packet from: "); XBeeAddress64 senderLongAddress = rx.getRemoteAddress64(); print32Bits(senderLongAddress.getMsb()); Serial.print(" "); print32Bits(senderLongAddress.getLsb()); Serial.println(' '); // this is the actual data you sent Serial.println("Received Data: "); for (int i = 0; i < rx.getDataLength(); i++) { print8Bits(rx.getData()[i]); Serial.print(' '); } //Received data as string to serial Serial.println(' '); Serial.println("In string format"); for (int i = 0; i < rx.getDataLength(); i++) { if (iscntrl(rx.getData()[i])) RecBuffer[i] =' '; else RecBuffer[i]=rx.getData()[i]; } Serial.println(RecBuffer); String myString = String((char *)RecBuffer); if(myString=="MTON"){ Serial.println("Switching on Motor"); } else if(myString=="MTOFF"){ Serial.println("Switching off Motor"); } } //clear the char array, other wise data remains in the //buffer and creates unwanted results. memset(&RecBuffer[0], 0, sizeof(RecBuffer)); memset(&Buffer[0], 0, sizeof(Buffer)); } //Send a packet every 4 sec. unsigned long currentMillis = millis(); if (currentMillis - previousMillis >= interval) { // save the last time you blinked the LED previousMillis = currentMillis; strcpy(Buffer,"RSLOW"); uint8_t payload[20]= "RSLOW"; // ZBTxRequest zbtx = ZBTxRequest(addr64,(uint8_t *)Buffer,sizeof(Buffer)); ZBTxRequest zbtx = ZBTxRequest(addr64,payload,sizeof(payload)); xbee.send(zbtx); } }


Burn the sketch to Arduino.


Run node js code in RPi and you start receiving the frames from Arduino.



Happy coding….

Written by Sony Arouje

January 21, 2016 at 12:06 am

VS2013 Multi-Device Hybrid Apps and Network Error in Windows8

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Last couple of days I was working on Node js REST service running in one of my Raspberry Pi. The idea is to do certain stuffs remotely via mobile devices. Later I will write a post explaining the project in detail. I completed Phase 1 of the application running in Raspberry pi. So next task was creating a mobile app, I decided to use Cordova with VS 2013 Multi Device Hybrid app template.

Yesterday night I started working on the Hybrid app in VS 2013 for Windows 8. First thing I wanted to test was the connectivity to the REST service running in Raspberry pi. I used Angular js $http to connect to the REST service. To my surprise what ever I do, the app is throwing error while doing http post with status 0. The same code works successfully if I run as a web app.

I spend a hell lot of time to figure out the issue but no success. Then I decided to use fiddler to test the traffic, when fiddler is running the app could able to communicate with the REST service. I got a hint, when we run Fiddler in Win8, it adds apps to AppContainer Loopback exemption. If I exempt my windows 8 app then http request starts failing. This stage I realized that, the error is because of some app configuration issue. Also in VS Java Script console I could see the error as shown below.

XMLHttpRequest: Network Error 0x2efd, Could not complete the operation due to error 00002efd.

All my google search return nothing. After a long hours of desperate research I came to know that to access private network I need to add Private Network capability to windows 8 app. But I didn’t know how to add it for Hybrid app as there is no Capabilities section in the config.xml. Some more search leads me to the Faq page of Multi device hybrid app template. As per the FAQ page we can override the default AppManifest.xml as shown below.

1. Create a Package.appxmanifest file under res/cert/windows8. Create a windows8 solution folder if not exist.

2. Open the project folder and go to bld/windows-AnyCpu/Debug and open AppxManifest.xml in notepad, copy the content and paste it in the above Package.appxmanifest file.

3. Double click on Package.appxmanifest file then goto Capabilities tab and choose ‘Private Networks (Client & Server)’.

4. Save it and run the app again, this time it worked I could connect to my Node js REST api.


Hope this will help some one to solve the XMLHttpRequest issue.


Happy Coding…

Written by Sony Arouje

October 29, 2014 at 3:50 pm

Bind JSON REST result using Knockout

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Last couple of hours I was trying to bind json data from a WCF service to a simple HTML UI using Knockout js. This is a very simple application I created to learn Knockout. This application is also a tracer to test  whether I can bind json result from the service directly to the UI, without creating an elaborate javascript view model at the client side. In real world services returns complex json, so it’s not possible to create the same model at the client side.


Knockout provides mapping as a plugin, you can see more details here. Please  go through the link before you proceed.

So let’s see how I created my view model and the html UI.

I created a js file named customerviewmodel.js and added the  below code.

function customerViewModel() {
    var self = this;

    self.customerList = ko.observableArray();

    self.getCustomers = function () {
            type: 'GET',   
            url: '',
            contentType: "application/javascript",
            dataType: "jsonp",
            success: function(data) {
                var observableData = ko.mapping.fromJS(data);
                var array = observableData();
            error:function(jq, st, error){

$(document).ready(function () {
    ko.applyBindings(new customerViewModel());

And the html UI. For this tracer app, I created a MVC4 web application and removed all the html code from the Views/Home/index.cshtml and replaced it with the below code.

<script src="~/Scripts/jquery-1.8.2.js"></script>
<script src="~/Scripts/knockout-2.2.0.debug.js"></script>
<script src="~/Scripts/knockout.mapping-latest.debug.js"></script>
<script src="~/MyScripts/customerviewmodel.js"></script>

    <tbody data-bind="foreach: customerList">
            <td data-bind="text: Id"></td>
            <td data-bind="text: Name"></td>

<input type="button" id="btnGetCustomers" value="Get Customers" data-bind="click: getCustomers">


customerList is a ko.observablearray and the data will get filled when the user clicks the button. I was able to call the WCF  REST api and get the json but unable to populate customerList or show the data to the  UI.  I fixed the issue with the  help of a post from Stackoverflow, see the code snippet below.


            success: function(data) {
                var observableData = ko.mapping.fromJS(data);
                var array = observableData();
WCF Configuration changes

As you can see, my WCF REST service is running in a different machine, and when I do an ajax call with datatype:json I am getting some errors. After some googling I came to know that I have to call the service with datatype:jsonp. So I changed it to jsonp and started getting the below error.


jQuery18206380491638767738_1396378264364 was not called


So I modified the  WCF service configuration as shown below to work with jsonp request.


          <binding name="webHttpBindingJson" crossDomainScriptAccessEnabled="true" />
        <behavior name="ServicesBehavior">
           <serviceMetadata httpGetEnabled="true"/>
        <behavior name="webby">
          <webHttp helpEnabled="true" />

I configured the service as shown below. I use a custom hosting, so need to provide baseaddresses.

      <service name="WCFRestTest.Services.CustomerService" behaviorConfiguration="ServicesBehavior">
            <add baseAddress=""/>
        <endpoint name="customerServiceRest" address="" 
               bindingConfiguration="webHttpBindingJson" binding="webHttpBinding" 
               contract="WCFRestTest.Services.ICustomerService" behaviorConfiguration="webby"/>


After this WCF configuration changes I could able to get json from the REST  api and bind the result to html UI using Knockout.

Let me know if you have any questions.


Happy coding…

Written by Sony Arouje

April 2, 2014 at 12:46 am

Posted in JavaScript

Tagged with , , ,

DDPClient.NET–.NET client for Meteor’s Distributed Data Protocol

with 3 comments

Last couple of hours I was working on a small .NET client library to connect to Meteor js application using Distributed Data Protocol (DDP). This post will give some insight to the library I am working on. You can see more details of DDP here.

Using DDPClient.NET you can subscribe to published items or call a Meteor method and display the same in your ASP.NET or Desktop applications.

First let’s go through the server code in my meteor application.

    Meteor.publish("allproducts", function(){
        return Products.find();
        console.log("starting Point of sale application.....");

        addProduct: function (prodCode, prodDesc) {
            return "Product Name: " + prodDesc + " Product Code: " + prodCode;


From the Meteor application we are publishing an item called ‘allproducts’ and have a server method called ‘addProduct’ that takes two parameters. Now let’s see how to subscribe to published item and call the server method using DDPClient.NET.

Subscribe to Published items


class Program
    static void Main(string[] args)
        IDataSubscriber subscriber = new Subscriber();
        DDPClient client = new DDPClient(subscriber);


public class Subscriber:IDataSubscriber
    public void DataReceived(dynamic data)
            if (data.type == "sub")
                Console.WriteLine(data.prodCode + ": " + data.prodName + 
                                         ": collection: " + data.collection);
        catch(Exception ex)


As you can see it’s very easy to connect to Meteor application using DDPClient.NET. Just call the Connection function with the url. Then call the subscribe function to subscribe to any published item in Meteor application.

In the above code I subscribed to ‘allproducts’ item. After you subscribed successfully to the meteor application, we will receive all the products stored in the db. Once our client is subscribed any insert/delete/update will streamed to the .NET client. You can test it by adding a some products via the web application and you can see the newly added product get displayed in the console.


How to call a Meteor Method?

class Program
    static void Main(string[] args)
        IDataSubscriber subscriber = new Subscriber();
        DDPClient client = new DDPClient(subscriber);

        client.Call("addProduct", "NS5", "IRobot");
public class Subscriber:IDataSubscriber
    public void DataReceived(dynamic data)
            if (data.type == "method")
        catch(Exception ex)

As you can see the Meteor method ‘addProduct’ take two arguments prodCode and prodDesc. So when we call the method we have to pass the parameter as well. We can do that by invoking the ‘Call’ function with the method name and arguments as shown below.

client.Call(“addProduct”, “NS5”, “IRobot”);


Also you will get notification if any data get deleted from the database. You can check the same as shown below.

else if (data.type == "unset")
    Console.WriteLine("deleleted item with id: " +; 

so you will get the id of the data it deleted, you can search for the product with this id and remove or do what ever you wanted to do.


DDPClient.NET is checked into Github. The meteor code I referred here is added to the one I used in  Getting Started with meteor.

Written by Sony Arouje

September 22, 2012 at 6:17 pm

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