siiky / etherscan_payments

EtherscanPayments

The Etherscan API key has to be set in the config/etherscan_key.exs file for the project to work.

Problem Statement

Please write a new Elixir Phoenix application capable of performing the following flow of tasks:

1. Have a web page that allows a user to enter an ETH transaction hash (tx_hash). This will simulate a payment throughout the challenge.
2. Receive the tx_hash and treat that as a sign that payment was received.
3. Perform confirmation of the payment. This can be done in a number of ways, but integrating with the Etherscan API or scrapping the specific tx_hash page are good starting points.
4. Once there are at least two block confirmations of the transaction, mark the payment as complete.

Other relevant points:

• There should be at least a test that exercises the submission of payment, feel free to add more.
• If you want to use a frontend framework for the web portion of the challenge, please use React. Using or not a frontend framework is completely up to you.
• Any styling should not use any frameworks such as Bootstrap or Foundation

Project Overview

Most of the files automatically created by Phoenix are "stock", not changed at all. The only routes are GET / and POST /:

page_path	GET /	EtherscanPaymentsWeb.PageController	:get
page_path	POST /	EtherscanPaymentsWeb.PageController	:post

The GET / endpoint just shows a form where a user may input a transation hash, with a submit action that POSTs said hash. The POST / endpoint simulates the transaction hash being received and handled (even though right now no action "requires" a POST).

Both routes are handled by the (default) page Page:

• lib/etherscan_payments_web/controllers/page_controller.ex
• lib/etherscan_payments_web/views/page_view.ex
• lib/etherscan_payments_web/templates/page/get.html.eex (corresponding to the GET endpoint)
• lib/etherscan_payments_web/templates/page/post.html.eex (corresponding to the POST endpoint)

The heart of the project is in the PageController, where the Etherscan API is called to get info for the received transaction hash. The Etherscan API documentation is very incomplete, and it took me several tries to learn of the relevant endpoints -- and even then, I haven't found where or how to obtain the number of block confirmations from the API. Another pain point was that the wanted info was spread across 3 different endpoints. With a rate limit of 5 API calls per second on Etherscan's end, one easily gets back "Max rate limit reached" replies. To fight this, I wrapped the required calls with a rate limiting library (can be found in the lib/etherscan_payments/EtherscanAPI.ex file). There's much to improve in this wrapper, but it serves its simple purpose as an MVP.

Errors were largely ignored for simplicity's sake. And so was CSRF protection.