Retrieving guard error messages

[SohamGhugare]

So I have a route which basically takes in a json request and tries to bind it to a struct. I have implemented the binding using the Json data guard, however I'm having issues retrieving the error message passed in by the guard when it fails.

#[post("/create", format="json", data="<user>")]
pub async fn create_user(user: Json<CreateUser>) -> Value {
    let user = User::new(user.into_inner());
    json!({
        "status": "ok",
        "user": user
    })
}

this is my route and when it fails, this is the error thrown,

Data guard `Json < CreateUser >` failed: Parse("{}", Error("missing field `name`", line: 1, column: 2)).

now I've implemented a catcher for the 422 status errors,

#[catch(422)]
pub fn general_unprocessable_entity(_req: &Request) -> Value {
    json!({
        "status": "error",
        "detail": "unprocessable entity"
    })
}

is there a way to pass the error message in the catcher, so instead of plain "unprocessable entity" it should say "unprocessable entity: missing field `name`"

[edgarogh]

I don't think that catchers have access to failing guard errors. The best way I know to do what you want to do is to catch the error inside your request handler.

use rocket::serde::json::Error as JsonError;

// A bit of boilerplate to save characters later

#[derive(Responder)]
#[response(status = 422)]
struct JsonErrorResponse(String);

impl From<JsonError> for JsonErrorResponse {
    fn from(err: JsonError) -> Self {
        Self(err.to_string())
    }
}

// Your original handler, that extracts a Result guard this time, and returns a Result

#[post("/create", format="json", data="<user>")]
pub async fn create_user(user_res: Result<Json<CreateUser>, JsonError>) -> Result<Value, JsonErrorResponse> {
    let user = user_res?;
    [...]
}

(The code is untested, I hope it works!)