Error Handling & Validation

use serde::Deserialize;
 
#[derive(Debug, Deserialize)]
struct Input {
    #[serde(deserialize_with = "bounded_string")]
    name: String,
}
 
fn bounded_string<'de, D: serde::Deserializer<'de>>(d: D) -> Result<String, D::Error> {
    let s = String::deserialize(d)?;
    if s.len() > 256 { return Err(serde::de::Error::custom("name too long")); }
    Ok(s)
}

use serde::Deserialize;
 
#[derive(Debug, Deserialize)]
#[serde(deny_unknown_fields)]
struct Signup {
    email: String,
    age: u8,
}
 
#[derive(Debug)]
enum ParseError {
    Serde(serde_json::Error),
    Business(&'static str),
}
 
fn parse_signup(raw: &str) -> Result<Signup, ParseError> {
    let body: Signup = serde_json::from_str(raw).map_err(ParseError::Serde)?;
    if !body.email.contains('@') {
        return Err(ParseError::Business("invalid email"));
    }
    if body.age < 18 {
        return Err(ParseError::Business("too young"));
    }
    Ok(body)
}
 
fn main() {
    let ok = parse_signup(r#"{"email":"a@b.co","age":21}"#).unwrap();
    assert_eq!(ok.email, "a@b.co");
 
    let extra = parse_signup(r#"{"email":"a@b.co","age":21,"admin":true}"#);
    assert!(extra.is_err());
}

// Map serde errors to HTTP 400
fn bad_request(err: serde_json::Error) -> ApiError {
    ApiError::BadRequest(err.to_string())
}