第一个实现

让我们看一下现在的请求处理程序:

//! src/routes/subscriptions.rs
#[derive(serde::Deserialize)]
pub struct FormData {
    email: String,
    name: String,
}

#[tracing::instrument(
    name = "Adding a new subscriber",
    skip(form, pool),
    fields(
        subscriber_email = %form.email,
        subscriber_name = %form.name,
    )
)]
pub async fn subscribe(form: web::Form<FormData>, pool: web::Data<PgPool>) -> HttpResponse {
    match insert_subscriber(&pool, &form).await {
        Ok(_) => HttpResponse::Ok().finish(),
        Err(_) => HttpResponse::InternalServerError().finish(),
    }
}
// [...]

我们的新验证应该放在哪里?

第一个草图可能看起来像这样:

// An extension trait to provide the `graphemes` method
// on `String` and `&str`
use unicode_segmentation::UnicodeSegmentation;

pub async fn subscribe(form: web::Form<FormData>, pool: web::Data<PgPool>) -> HttpResponse {
    if !is_valid_name(&form.name) {
        return HttpResponse::BadRequest().finish();
    }
    match insert_subscriber(&pool, &form).await {
        Ok(_) => HttpResponse::Ok().finish(),
        Err(_) => HttpResponse::InternalServerError().finish(),
    }
}

/// Returns `true` if the input satisfies all our validation constrains
/// on subscriber names, `false` otherwise.
pub fn is_valid_name(s: &str) -> bool {
    // `.trim()` returns a view over the input `s` without trailing
    // whitespace-like characters.
    // `.is_empty` checks if the view contains any character.
    let is_empty_or_whitespace = s.trim().is_empty();
    
    // A grapheme is defined by the Unicode standard as a "user-perceived"
    // character: `å` is a single grapheme, but it is composed of two characters
    // (`a` and `̊`).
    //
    // `graphemes` returns an iterator over the graphemes in the input `s`.
    // `true` specifies that we want to use the extended grapheme definition set,
    // the recommended one.
    let is_too_long = s.graphemes(true).count() > 256;

    // Iterate over all characters in the input `s` to check if any of them matches
    // one of the characters in the forbidden array.
    let forbidden_characters = ['/', '(', ')', '"', '<', '>', '\\', '{', '}'];
    let contains_forbidden_characters = s.chars().any(|g| forbidden_characters.contains(&g));
   
    // Return `false` if any of our conditions have been violated
    !(is_empty_or_whitespace || is_too_long || contains_forbidden_characters)
}

为了成功编译新函数，我们必须将 unicode-segmentation crate 添加到我们的依赖项中:

cargo add unicode-segmentation

虽然它看起来是一个完美的解决方案（假设我们添加一堆测试），但像 is_valid_name 这样的函数会给我们一种虚假的安全感。