Here at Pushe we have a server which we frequently send messages to from our IOS applications. However, the server code is full of bugs and we often lose the message data if it fails to handle a request successfully. And no one here is willing to fix it!!
In this challenge you are going to help us resolve this problem. Don't worry though, you won't have to debug our server code. Instead we want you to develop a reliable-messaging library for IOS which will guarantee that our requests are received and processed successfully.
Our server is hosted at https://challenge.ronash.co/reliable-messaging. The server accepts HTTP POST requests. If it succeeds in handling a request it will respond with a 200 status code and if it fails it will respond with 500.
For this challenge you will need to implement a reliable-messaging library and a sample application which utilizes the library.
The library should provide a simple API method which we will call to send messages to a server. The method should accept as parameters the URL which we want to send our message to and the message data we want to send (as a dictionary). It will then send a POST request to the URL with the provided message data. The API method should work asynchronously, meaning once it is called it should not wait for the data to be sent successfully and instead should return immediately.
Once the message is given to the library, it should guarantee that it will be sent to and handled by the server. For this purpose, if your initial POST request was unsuccessful you should retry until you receive a successful response (a 200 status code).
The following should also be taken into consideration:
- Retry attempts should be delayed with an exponential backoff policy.
- The library should be able to handle multiple messages, i.e., it should accept new messages even if the previous ones have not been successfully sent yet.
- The messages should be persisted, i.e., if the application closes before the messages are successfully sent then the messages should be attempted again once the application opens.
- [Optional] Provide a way for the application to be informed once a message has successfully been sent by the library (e.g., using callbacks, Future/Promise).
- [Optional] For the main part of the challenge we only require that you implement the functionality for when the app is in the foreground. However, as a bonus you may also implement sending messages when the app is in the background. In this case if the app goes into the background before the messages have successfully been sent, they should be retried even while the app is in the background.
You should also write tests to show that your library works as intended. Use the testing framework of your choice.
Create a sample application to show how to use your library. The application should contain a single screen which includes a text field and a button and it should use the library to send the contents of the text field to the server every time the button is clicked.
- You may implement the challenge using either Objective-C or Swift.
- You may use third-party libraries (e.g., for HTTP requests, ReactiveX, ...) as long as they were not designed specifically for the problem defined in the challenge.
- Clean, readable and maintainable code is an important factor in our evaluation.
- There is no time constraint for the challenge. However, we do not want it to take too much of your time. If you feel like you have spent sufficient time and it is not yet complete you may still send it to us and we will review it. In this case let us know how much time you managed to put for the challenge.
- Fork this repository and start coding.
- Commit and push your code to your new repository.
- Once complete, send a pull request and we will review your code and get back to you.