How to Handle Untrusted Input Safely in Rust

Handle untrusted input by validating and sanitizing it before use, typically by parsing strings into safe types or using libraries that enforce constraints. In Rust, avoid directly using raw input from std::io::stdin() for logic; instead, parse it with parse() or use crates like validator to ensure safety.

use std::io;

fn main() {
    println!("Please input your guess.");
    let mut guess = String::new();
    io::stdin()
        .read_line(&mut guess)
        .expect("Failed to read line");

    let guess: u32 = guess.trim().parse()
        .expect("Please type a number!");

    println!("You guessed: {guess}");
}

Untrusted input is any data coming from outside your program, like user keystrokes or network requests, which could be malicious or malformed. You must check this data to ensure it fits your expected format before using it, similar to a security guard checking IDs before letting people into a building. Rust helps by forcing you to handle potential errors during this conversion process.