Input validation is a critical part of any application, whether it be a web app, mobile app, or desktop app. Without proper input validation, an application is vulnerable to all sorts of attacks, including SQL injection, cross-site scripting (XSS), and man-in-the-middle (MITM) attacks.
In this article, we'll take a look at some best practices for input validation in Kotlin, as well as some common pitfalls to avoid.
There are many different libraries and frameworks available for input validation in Kotlin. It's important to choose the right one for the job, based on the requirements of the project.
For example, the kotlinx.html library provides a set of functions and objects for validating HTML input. The kotlinx.validation library provides a set of functions and objects for validating XML input.
Before starting to code, it's important to define the validation rules that need to be implemented. This will help to avoid duplication of code and will make the code easier to maintain.
When defining validation rules, it's best to use explicit types. For example, instead of using the Any type, it's better to use the specific type, such as String or Int.
Nullable types should be avoided when possible, as they can lead to unexpected results. If a nullable type is absolutely necessary, it's best to use a library that provides null-safety, such as the kotlinx.validation library.
When writing validation code, it's best to use positive assertions. In other words, the validation code should check for the presence of a particular value, rather than the absence of a value.
Kotlin's short-circuiting behaviour can lead to unexpected results when used in conjunction with input validation. For example, consider the following code:
fun validateInput(input: String): Boolean {
// Validation code here
}
fun main() {
val input = "test"
if (validateInput(input) && input.isNotEmpty()) {
// Do something with the input
}
}
In this code, the validateInput() function is called first, and then the input.isNotEmpty() function is called. However, due to Kotlin's short-circuiting behaviour, the input.isNotEmpty() function will never be called if the validateInput() function returns false.
To avoid this issue, it's best to use the let() function, as follows:
fun validateInput(input: String): Boolean {
// Validation code here
}
fun main() {
val input = "test"
input.let {
if (validateInput(it) && it.isNotEmpty()) {
// Do something with the input
}
}
}
In this code, the let() function is used to invoke the validateInput() function and the input.isNotEmpty() function. This ensures that both functions are always called, regardless of the return value of the validateInput() function.
One of the most common mistakes made when coding is not validating input. This can lead to all sorts of security issues, as well as data corruption.
It's important to always validate input, even if it's coming from a trusted source.
Another common mistake is to rely on client-side validation, such as HTML5 form validation. While client-side validation can be useful, it should never be used as the sole means of validation.
This is because client-side validation can be bypassed by malicious users. Therefore, it's important to always validate input on the server-side as well.
A common pitfall when validating input is to only check for specific characters, such as alphanumeric characters. However, this can lead to security issues, as malicious users can bypass the validation by using other characters.
It's important to always validate input against a whitelist of allowed characters, rather than a blacklist of disallowed characters.
Another common mistake is to forget to sanitize output. This can lead to security issues, such as cross-site scripting (XSS) attacks.
It's important to always sanitize output before displaying it to the user.
A common mistake when using regular expressions (regex) for input validation is to use a single regex for all input. However, this can lead to performance issues, as the regex will need to be re-compiled for each input.
It's best to use a different regex for each input, or to compile the regex beforehand.
Input validation is a critical part of any application. In this article, we've covered some best practices for input validation in Kotlin, as well as some common pitfalls to avoid.