Implement the Fuzz Target

Now that we know what a slice is, we can implement our function. Remember our function skeleton from our lib.rs:

#![allow(unused)]
fn main() {
pub fn decode(mut encoded_input: &[u8]) -> Vec<u8> {
    Vec::new()
}
}

We'll implement a simple decoder for URL-encoded text. URL-encoding looks something like This%20string%20is%20URL%20encoded. We want to have a bug in this program that causes it to crash, so we will use a bit of unsafe Rust. You can read all about unsafe Rust here but basically the unsafe keyword lets you:

• Dereference a raw pointer
• Call an unsafe function or method
• Access or modify a mutable static variable
• Implement an unsafe trait
• Access fields of unions

We'll use it to program like we're writing C/C++. You don't need to do this (there's a perfectly good safe implementation of URL decoding), we're just doing it for an example of a fuzz target that will actually crash.