Applications with Rullst I · Lesson 06 / 14

Validate at the right boundary

A direct request does not pass through form rules.

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1
NewMission describes the expected shape; Deserialize reads JSON and deny_unknown_fields rejects extra fields. Then validate applies domain rules. Converting JSON into a struct does not prove an empty title or priority 9 makes sense.
2
The title is trimmed, must contain 1–80 Unicode code points and rejects control characters such as newlines. chars().count() counts neither bytes nor necessarily perceived symbols: some emoji combine several code points. Priority must be between 1 and 3.
3
Predict results for an all-space title, 80 é letters, 81 x letters and priority 0. Run cargo test --locked title_and_priority_boundaries. The é test distinguishes code points from UTF-8 bytes; also use an emoji example to explain the measure’s limit.
4
In the handler, validate comes before store.create. Failure returns 422 with an error code and inserts no record. The HTTP test calls the API directly, without relying on browser required, and checks that the count did not change.

Your application workbench

The kit includes a complete app to investigate and modify. The excerpt below explains this step; the editor contains the indicated file. Rullst Academy does not compile or run this server in your browser.

File to study and modify

src/validation.rs

let title = input.title.trim().to_owned();
if !(1..=80).contains(&title.chars().count()) {
    return Err("invalid_title");
}

Extract the kit to a new folder and open a terminal beside Cargo.toml. Use Rust 1.96+; the first build may download dependencies and take time. Then open http://127.0.0.1:3010. Stop with Ctrl+C and run again after editing.

cargo test --locked
cargo run --locked

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Official links and next step

✦

YOUR MISSION

Test boundaries and reject invalid input before changing the database.

Take it with you

In a copy, change the limit to 60. Update the rule, new-schema CHECK, interface explanation and 60/61 tests. Use a new test database: CREATE TABLE IF NOT EXISTS does not alter an existing table. Explain why changing text alone is insufficient.

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My code or notes

use serde::Deserialize;

#[derive(Deserialize)]
#[serde(deny_unknown_fields)]
pub struct NewMission {
    pub title: String,
    pub priority: i64,
}

#[derive(Deserialize)]
#[serde(deny_unknown_fields)]
pub struct Completion {
    pub done: bool,
}

pub fn validate(input: NewMission) -> Result<NewMission, &'static str> {
    let title = input.title.trim().to_owned();
    if !(1..=80).contains(&title.chars().count()) || title.chars().any(char::is_control) {
        return Err("invalid_title");
    }
    if !(1..=3).contains(&input.priority) {
        return Err("invalid_priority");
    }
    Ok(NewMission {
        title,
        priority: input.priority,
    })
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn title_and_priority_boundaries() {
        for title in ["", "   ", "line\nbreak", &"x".repeat(81)] {
            assert!(
                validate(NewMission {
                    title: title.into(),
                    priority: 1
                })
                .is_err()
            );
        }
        for priority in [0, 4, -1] {
            assert!(
                validate(NewMission {
                    title: "Orbit".into(),
                    priority
                })
                .is_err()
            );
        }
        let input = validate(NewMission {
            title: format!(" {} ", "é".repeat(80)),
            priority: 3,
        })
        .unwrap();
        assert_eq!(input.title.chars().count(), 80);
        assert_eq!(input.priority, 3);
    }
}

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Validate at the right boundary

Let's discover together

Your application workbench

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Decide before running

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