how to return error as a Json from FromParam #2714

mtumilowicz · 2024-01-27T17:25:48Z

What kind of documentation problem are you reporting?

Technical Problem

Where is the issue found?

https://api.rocket.rs/v0.5/rocket/request/trait.FromParam.html

What's wrong?

what I would like to have: returning error in json format from FromParam

expectations

something like this, but using FromParam:

#[derive(Serialize)]
pub struct ErrorApiOutput(HashMap<&'static str, Vec<Cow<'static, str>>>);

pub fn for_key(key: &'static str, message: Cow<'static, str>) -> ErrorApiOutput {
    let mut data = HashMap::new();
    data.insert(key, vec![message]);

    ErrorApiOutput::new(data)
}

fn parse_customer_id(customer_id: &str) -> Result<CustomerId, Custom<Json<ErrorApiOutput>>> {
    match Uuid::parse_str(customer_id) {
        Ok(uuid) => Ok(CustomerId::new(uuid)),
        Err(_) => {
            let output = ErrorApiOutput::for_key("customer_id", Cow::Borrowed("is not a correct uuid"));
            Err(Custom(Status::UnprocessableEntity, Json(output)))
        }
    }
}

so: to parse correctly CustomerId or to return UnprocessableEntity with json body:

{
    "customer_id": [
        "is not a correct uuid"
    ]
}

code:

use rocket::{get, launch, routes};
use rocket::http::{ContentType, Status};
use rocket::local::blocking::Client;
use rocket::request::FromParam;
use rocket::response::status::NotFound;
use rocket::serde::json::{Json, json};
use rocket::serde::uuid::Uuid;

struct CustomerId(Uuid);

#[derive(Debug)]
struct ErrorApiOutput {
    error: String
}

impl<'r> FromParam<'r> for CustomerId {
    type Error = Json<ErrorApiOutput>;

    fn from_param(param: &'r str) -> Result<Self, Self::Error> {
        match Uuid::parse_str(param) {
            Ok(uuid) => Ok(CustomerId(uuid)),
            Err(_) => Err(Json(ErrorApiOutput { error: "malformed uuid".to_string() })),
        }
    }
}

#[get("/customers/<customer_id>")]
pub fn get_customer(customer_id: Uuid) -> Result<String, NotFound<String>> {
    Ok(customer_id.to_string())
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/api", routes![get_customer])
}

#[test] // working
fn test_get_customer_correct_uuid() {
    let client = Client::tracked(rocket()).expect("valid Rocket instance");

    let response = client.get("/api/customers/550e8400-e29b-41d4-a716-446655440000").dispatch();

    assert_eq!(response.status(), Status::Ok);
    assert_eq!(
        response.into_string(),
        Some("550e8400-e29b-41d4-a716-446655440000".to_string())
    );
}

#[test] // not working
fn test_get_customer_incorrect_uuid() {
    let client = Client::tracked(rocket()).expect("valid Rocket instance");

    let response = client.get("/api/customers/invalid-uuid").dispatch();

    assert_eq!(response.status(), Status::UnprocessableEntity);
    assert_eq!(response.content_type(), Some(ContentType::JSON));
    assert_eq!(
        response.into_string(),
        Some(json!({"error": "malformed uuid"}).to_string())
    );
}

problem

I specified FromParam to parse String into CustomerId(Uuid); when it is not correct I want to show appropriate error as a Json

as I checked with curl: curl http://localhost:8000/api/customers/550e8400-e29b-41d4-a716-44665544000

html is returned, and it does not contain appropriate error message

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta name="color-scheme" content="light dark">
    <title>422 Unprocessable Entity</title>
</head>
<body align="center">
    <div role="main" align="center">
        <h1>422: Unprocessable Entity</h1>
        <p>The request was well-formed but was unable to be followed due to semantic errors.</p>
        <hr />
    </div>
    <div role="contentinfo" align="center">
        <small>Rocket</small>
    </div>
</body>
</html>

what is more - documentation does not specify how to return Json for that case

System Checks

I confirmed that the issue still exists on master on GitHub.
I was unable to find a previous report of this problem.

The text was updated successfully, but these errors were encountered:

SergioBenitez · 2024-01-30T17:25:56Z

The easiest thing to do is this:

type ApiResult<T> = Result<T, Custom<Json<ErrorApiOutput>>>;

#[get("/customers/<customer_id>")]
pub fn get_customer(customer_id: ApiResult<CustomerId>) -> ApiResult<String> {
    let id = customer_id?;
    Ok(id.to_string())
}

mtumilowicz · 2024-01-30T19:55:12Z

working! thank u very much

@SergioBenitez do u think that we should update documentation? for me connection between FromParam and input type of param in endpoint was not clear

fully working code for ref:

use rocket::{launch};

use rocket::{get, routes};
use rocket::http::{ContentType, Status};
use rocket::local::blocking::Client;
use rocket::request::FromParam;
use rocket::response::status::{Custom};
use rocket::serde::json::{Json, json};
use rocket::serde::uuid::Uuid;
use serde_derive::Serialize;

struct CustomerId(Uuid);

#[derive(Debug, Serialize)]
struct ErrorApiOutput {
    error: String,
}

impl<'r> FromParam<'r> for CustomerId {
    type Error = Custom<Json<ErrorApiOutput>>;

    fn from_param(param: &'r str) -> Result<Self, Self::Error> {
        match Uuid::parse_str(param) {
            Ok(uuid) => Ok(CustomerId(uuid)),
            Err(_) => Err(Custom(Status::UnprocessableEntity, Json(ErrorApiOutput { error: "malformed uuid".to_string() }))),
        }
    }
}

type ApiResult<T> = Result<T, Custom<Json<ErrorApiOutput>>>;

#[get("/customers/<customer_id>")]
pub fn get_customer(customer_id: Result<CustomerId, Custom<Json<ErrorApiOutput>>>) -> Result<String, Custom<Json<ErrorApiOutput>>> {
    let id = customer_id?;
    Ok(id.0.to_string())
}

#[launch]
fn rocket() -> _ {
    rocket::build().mount("/api", routes![get_customer])
}

#[test] // working
fn test_get_customer_correct_uuid() {
    let client = Client::tracked(rocket()).expect("valid Rocket instance");

    let response = client.get("/api/customers/550e8400-e29b-41d4-a716-446655440000").dispatch();

    assert_eq!(response.status(), Status::Ok);
    assert_eq!(
        response.into_string(),
        Some("550e8400-e29b-41d4-a716-446655440000".to_string())
    );
}

#[test] // working
fn test_get_customer_incorrect_uuid() {
    let client = Client::tracked(rocket()).expect("valid Rocket instance");

    let response = client.get("/api/customers/invalid-uuid").dispatch();

    assert_eq!(response.status(), Status::UnprocessableEntity);
    assert_eq!(response.content_type(), Some(ContentType::JSON));
    assert_eq!(
        response.into_string(),
        Some(json!({"error": "malformed uuid"}).to_string())
    );
}

SergioBenitez · 2024-01-31T04:00:54Z

This is already mentioned here: https://rocket.rs/v0.5/guide/requests/#fallible-guards. But I'll keep this in mind for future iteration of the docs.

P.S: You created a type alias that you then don't use. You should use it to clean up the code a bit.

mtumilowicz added the docs Improvements or additions to documentation label Jan 27, 2024

SergioBenitez closed this as not planned Won't fix, can't repro, duplicate, stale Jan 31, 2024

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how to return error as a Json from FromParam #2714

how to return error as a Json from FromParam #2714

mtumilowicz commented Jan 27, 2024 •

edited

SergioBenitez commented Jan 30, 2024

mtumilowicz commented Jan 30, 2024 •

edited

SergioBenitez commented Jan 31, 2024

how to return error as a Json from FromParam #2714

how to return error as a Json from FromParam #2714

Comments

mtumilowicz commented Jan 27, 2024 • edited

What kind of documentation problem are you reporting?

Where is the issue found?

What's wrong?

expectations

code:

problem

System Checks

SergioBenitez commented Jan 30, 2024

mtumilowicz commented Jan 30, 2024 • edited

SergioBenitez commented Jan 31, 2024

mtumilowicz commented Jan 27, 2024 •

edited

mtumilowicz commented Jan 30, 2024 •

edited