There are three things a software developer can watch forever: fire, water, and request validators. In the previous blog post, I demonstrated how to develop a simple REST API application with http4s. But that app has a drawback — the user can send any invalid data to the API and it will be processed with no error messages.
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The Problem
The main problem of 99.99 percent of web apps is that they have users (and feel free to tweet this). As a result, there is a huge human factor, which leads to a tremendous amount of inappropriate interactions with web applications. One of my favorites is invalid data input. For example, the user may enter "blablabla" in an email field, "MyNickName" in a phone number field or even leave a form field empty when it's required.