Rust: wrapper for jsonwebtoken and serde Deserialize

April 2, 2022

I am writing a Rust wrapper to sign and decode a given struct.

The create_token method seems to work: but the decode_token return an error on compile time about the lifetimes:

use jsonwebtoken::{decode, encode, Algorithm, DecodingKey, EncodingKey, Header, Validation};
use serde::{Deserialize, Serialize};

const JWT_SECRET: &[u8] = b"secret";

pub struct TokenService;

impl<'de> TokenService {
  pub fn create_token<T: Serialize>(data: T) -> String {
    let header = Header::new(Algorithm::HS512);

    let token = encode(&header, &data, &EncodingKey::from_secret(JWT_SECRET)).unwrap();

    token
  }

  pub fn decode_token<T: Deserialize<'de>>(data: &str) -> T {
    let decoded = decode::<T>(&data, &DecodingKey::from_secret(JWT_SECRET), &Validation::new(Algorithm::HS512)).unwrap();
    //                     ^ Error here
    decoded
  }
}

the trait bound `for<'de> T: types::errors::_::_serde::Deserialize<'de>` is not satisfied

the trait `for<'de> types::errors::_::_serde::Deserialize<'de>` is not implemented for `T`

note: required because of the requirements on the impl of `rocket::serde::DeserializeOwned` for `T`

I am not sure where should I add this missing lifetime. Any help will be welcome.

>Solution :

Usually T would need to be constrained to DeserializeOwned:

pub fn decode_token<T: DeserializeOwned>(data: &str) -> T {
    let decoded = decode::<T>(&data, &DecodingKey::from_secret(JWT_SECRET), &Validation::new(Algorithm::HS512)).unwrap();
    decoded
}