Saturday, November 30, 2019

How to do iOS Receipt Validation in Objective-C

Until you do it yourself, receipt validation might feel like one of the most unclear topic, when it comes to verifying In App Purchases (IAP) on iOS platform for an App Developer.

This post documents the exact steps and code needed to perform receipt validation with AppStore.

The Receipt

As soon as the app is installed or updated, Apple puts a purchase receipt (signed by Apple via AppStore) in the main bundle of the app.

Think of the receipt as the trusted record of a purchase. It also includes any in-app purchases that the user might have made.

Receipt Validation

By verifying the receipts, App Developers can protect their revenue and enforce their business model directly in their application. Receipt Validation plays a key role in verifying whether the auto-renewing subscription is currently active or not.

Here are the steps needed to validate the receipt.
  • First step in the process is to load the receipt from apps main bundle
  • If the receipt is not found, we could refresh the receipt using SKReceiptRefreshRequest
    • This is especially helpful during development and debugging.
  • Refreshing the receipt tells the system that the application needs to retrieve a new receipt

  • Before we could send the receipt information to AppStore, we will need the App's Shared Secret.
  • To get this, log on to itunesconnect and navigate to My Apps -> Click on your App -> Click on Features 
  • Click on the In-App Purchases section. On the right side you will see the link App-Specific Shared Secret, click this link to generate the App-Specific Shared Secret. It will pop up a dialog where you could generate a new secret or view the existing secret.
  • Note down the generate secret somewhere, we need to pass this value to AppStore for receipt verification.

  • Next, we need send the receipt details along with App-Specific Shared Secret to AppStore. We have to hit different URL based on whether the app is running in the sandbox environment or production environment.
  • Now we need to send the Base 64 encoded receipt information along with App-Specific shared secret to the AppStore API. The response of this API is a JSON object with details about various purchases user has made on the app.
  • Full list of receipt fields found in this JSON response can be found here
  • "latest_receipt_info" field is part of the JSON response. It is an Array containing the details of IAP and Subscription purchases made by the user on the app. 
  • Each purchase holds information like
    • Which product was purchased: "product_id"
    • When was the purchase made: "original_purchase_date"
    • Whether or not the auto-renewing subscription is running the trial period: "is_trial_period"
    • The date of the auto-renewing subscription expires: "expires_date"
    • What was the intent behind the subscription expiration: "expiration_intent"
  • Now all that is left is to parse the JSON response and iterate through the contents of "latest_receipt_info" field. Here's the code that does it.

Thats about all that is needed to perform receipt validation.

However, please note that, since we can't build a trusted connection between a user’s device and the App Store directly, we should should always call AppStore receipt validation API from a trusted server. Details of how to do that, is out of scope of this post.

Thursday, October 31, 2019

How to upgrade PostgreSQL to 11.4 from 10 on MacOS

I recently updated my PostgreSQL to version 11.4 from 10.0. After the upgrade, I realised that I wasn't able to start my PostgreSQL server. It kept giving me the following error:

The data directory was initialized by PostgreSQL version 10.0, which is not compatible with this version 11.4.

I had to follow bunch of steps to get back my old databases to work with PostgreSQL 11.4. This post is an attempt to document those steps for future reference.

The Solution

  • Install the older version of PostgreSQL using the following command
  • Output would be very similar to these messages
  • Unlink the newly installed older version of PostgreSQL. Brew will spit out the message confirming that the unlinking was successful.
  • Link the latest version of PostgreSQL. As before, brew will spit out the message stating that the linking was successful.
  • Move the data directory from default location to another location
  • Use initdb to initialise a new and empty data directory.
  • Output might look somewhat like this
  • Copy over the timezone and timezonesets directory to /usr/local/share/postgresql10
  • Upgrade the data directory using the following command
  • It will do bunch of things and might spit out messages like these
  • Moment of truth, start the PostgreSQL server
  • If everything goes through fine, you should see a message that states that PostgreSQL server was started successfully.
  • Cleanup steps
Thats about it! We have successfully upgraded PostgreSQL to 11.4 from 10.

Sunday, September 29, 2019

How to setup an Alarm when RDS is running on low free disk space

Yea, that happened to me!

The Problem

My RDS instance suddenly ran out of space and some of our applications started failing left, right and centre. It was a disaster and a fair bit of fire fighting was involved.

I told to myself, how did this happen? I should have put checks in place to ensure this didn't happen. I should have added some sort of alarm to warn when free disk space is low.

To deal with this, we wanted to first setup an alarm to notify the team when RDS instance is running on low free disk space. Looked at AWS console to create the alarm, but - I must admit - we were a bit surprised to see that there isn't like a straightforward way to create this type of an alarm.

The Solution

After a little googling, we found the way to setup the Alarm. This post is to document the steps involved in getting this done so that, I do not forget them :D

We basically need to do the following

  • Create an SNS topic to that can send emails
  • Subscribe the team email address to the SNS topic
  • Confirm the email subscription by clicking on the link that AWS sends.
  • Create a cloud watch alarm to send the alert when the RDS free disk space is lesser than the chosen threshold

That's all there is to it!

Saturday, August 31, 2019

How to restart AWS Elastic BeanStalk instances on a schedule

We wanted to restart all AWS Elastic BeanStalk instances at a given time during the day, every day. To perform this task, there are many solutions. Some of them involve, setting up a lambda function and writing some code etc, what we wanted was something quick and not a maintenance nightmare.

Hence, I thought, all we need to do is re-start the instance on a schedule, whats the best way to do it? Cron jobs flashed as a possible answer!

The Problem

The environment we were talking about was an Elastic BeanStalk Auto-Scaling environment, which meant that EC2 instances will be added and removed on demand.

If we were going to use cron jobs, we needed to make sure that whatever instances are currently in service, they all honour the cron job at all times. This means, new instances that get added on demand, in service should automatically have the cron jobs setup on them too!

The Solution

To do this in the easiest possible way, we ended up using the Advanced Environment Customization with Configuration Files (.ebextensions). AWS Elastic BeanStalk has a feature where we could provide configuration files bundled with our web application source code. These files are basically configuration files under the directory named ".ebextensions".

Now, to setup the cron job reliably on Elastic BeanStalk instances, all we needed to do was to add the "cron-linux.config" file under the ".ebextensions" directory and bundle it with the application source code which gets deployed to the environment.

The folder structure would look like this

The cron-linux.config will be YAML file. Here are sample contents of the cron-linux.config file, this setup re-starts the Elastic BeanStalk instance every day at 0530 hrs.

Thats about it, deploying this along with you source bundle on the environment ensures that the environment instances are restarted every day at 0530 hrs without fail!

Wednesday, July 31, 2019

Majestic Meghalaya - Part 3

This is the last post that will cover the remainder of our mesmerising trip to Meghalaya. If you haven't already checked out the Part 1 and Part 2 of this series, I would strongly encourage you to do so right away.

After a full day trek to the Double Decker Living Root Bridge it was time to relax and spend the evening at the hotel. Next day we visited the beautiful town of Cherrapunji. It has got some breath taking scenery. We saw a tall waterfall called the NohKalikai waterfall. It's a very tall waterfall with beautiful stream of water falling throughout the year. It also has an interesting back story to it on why it was named NohKalikai, I am not going to tell the story because locals do an amazing job at narrating it and I don't want to spoil the fun.


After breathing in the beauty of NohKalikai waterfall, we moved on to visit the Mawsmai Cave. The caves are beautiful well maintained. At some points you will have to cross natural water, while at others you have to pass through very narrow zone, overall a great experience.



Next we visited one of the lesser know places called the Garden of Caves near Cherrapunji, it's a beautiful place with lots of things to see in it. We also drank the medicinal mountain water and collected a bit of it in a lush green bamboo stick to carry it along with us.


It was now time to say good bye to Cherrapunji and move on to the last destination in our trip. The formidable Kaziranga National Park.  By late evening we reached our hotel at the Kaziranga National Park. We were all very excited for the next day, especially because in the morning we will be visiting the Park for an Elephant back safari!

Next day, we all woke up very early and reached the Kaziranga National Park gate well in time. Before this I had been to many Jeep and Bus Safaris, but an Elephant Back Safari was a first time event for me. It is one of a kind experience! You basically get to sit on the elephant and mahout takes us in the jungle to see Rhino's, Tiger's, Deer's, Bird's and other wild creatures. 

A funny incident happened during our ride, our elephant decided to race with other elephant nearby and for a good minute or so we were forced participants to our very first elephant race! It was both funny and adventurous at the same time :D

After this safari, we did 2 more Jeep safari one in the evening and another in the morning the next day.
 In addition to the wild animals, Kaziranga National Park is filled with rich flora and fauna.
In the evenings, after the safari we saw the traditional north east cultural program. Lots of talented artists can be seen performing, while wearing traditional north east attire. I would strongly recommend everyone to see it at least once.


Truly, the trip to Meghalay was majestic and mesmerizing. We came back with our hearts filled with joy and lots of love for the beautiful state and its lovely people!

Sunday, June 30, 2019

Majestic Meghalaya - Part 2

In this post, I will cover the remainder of our mesmerising trip to Meghalaya. If you haven't already checked out the Part 1 of this series, I would strongly encourage you to do so right away.

After visiting the beautiful Umngot river, we visited a true natural wonder. The single decker living root bridge, its a natural marvel and I was blown away looking at its awesomeness! 

These wonderful structures have meticulously grown over a period of time and are among the biggest attractions in Meghalaya. In fact I would say this, if you could only see one natural wonder in your life then, do visit the natural wonder of Living Root Bridges in Meghalaya.

No photograph or written literature can justify its beauty, it's one of those things, "You got to see it, to believe it!"
Single Decker Living Root Bridge
We trekked a bit to see the beautiful bamboo tree top structure which watches over the India-Bangladesh border. We reached there at the right time to see the beautiful evening sky.

Evening Sky at India-Bangladesh border view point
After a satisfying day filled with beautiful experiences we were ready to crash into our home stay cottage at Mawlynnong - Asia's cleanest village.

The village is extremely clean, the best thing about this place is, you cannot find any barren piece of land. Every lane, every corner is covered with beautiful greenery. 

We had an enchanting experience while doing our morning walk in the village.



After our hearts were filled with beautiful memories of Mawlynnong, it was time to start moving towards Cherrapunji.

Cherrapunji is also called "Scotland of the East" and it does full justice to this title. Its one of the most beautiful places I have ever visited. On the day when we reached Cherrapunji we decided to do a trek to see the beautiful Double Decker Living Root Bridge. It takes about 8 hrs to go to and fro, but it's well worth the time. One has to climb up/down about 3000 steps one way before you can reach the Double Decker Living Root Bridge. 

The journey itself is extremely beautiful, you pass through beautiful waterfalls filled with turquoise water


You also pass through a couple of hanging bridge, while walking on them you can clearly see whats below you and its quite a thrilling experience.


After the trek and enjoying beautiful nature all along, we finally reached the Double Decker Living Root Bridge and boy what a sight it was!

Double Decker Living Root Bridge


Seeing the Single Decker Living Root Bridge is a marvel in itself, looking at a Double Decker version is beyond words. Near the Bridge there is a small waterfall a water pool. In the pool there are hundreds of small fishes which give you free foot pedicure!


I had initially though, I would fully describe the remainder of our Meghalaya trip in this post, but there is just so much to see and so much to share, it deserves a few more posts!

Sunday, May 26, 2019

Majestic Meghalaya - Part 1

We were looking out for next holiday destination for a family vacations. After evaluating a few options, we narrowed it down to Meghalaya. We had already been to Sikkim earlier and we were extremely impressed with its beauty and overall we had a very memorable experience. We were expecting the same and more from Meghalaya. We booked the customised itinerary via Travel Triangle

I was in for a very pleasant surprise, Meghalaya is not only culturally very rich but also extremely beautiful. The mountains, picturesque villages, beautiful water bodies, lovely landscapes, you name it and its there!

We landed in Gangtok and went straight to the famous Kamakhya Temple. It's a beautiful temple with rich history.

Kamakhya Temple

We reached Shillong pretty late in the evening so we decided crash at the hotel. Next morning, we were greeted with jaw dropping landscapes, beautiful cherry blossoms in full bloom, and beautiful gardens.






Cherry Blossoms

Wards Lake

One important thing that we noticed as soon as we entered Meghalaya is the amount of cleanliness maintained by each and every individual, this is I think a common sight in the entire north east. Sikkim was super clean too!

Next day, we continued our journey towards Dawki and Umgot, on the way you can see some majestic views of mountains with full green cover.


At Dawki you can see the India-Bangladesh border and the friendship gate.

Next we went for a boating trip on the Umgot river.


Umgot river is a beautiful river, you can see the bottom of the river bed through the crystal clear water!



By this time, we were truly mesmerised by the beauty of Meghalaya. In the next post, I will cover the remainder of our trip.

Have some Fun!