This exists to encapsulate a number of common patterns when returning errors from Axum routes. These patterns include:

• wanting to return error responses as a JSON object
• to automatically convert errors raised in the route hander into that standardised JSON response
• provide appropriate default error messages for public use, which takes into account the status code in use
• a need to optionally add extra data to the error JSON output

A basic tutorial

Below is a mock example route to download a User object:

```rust use ::axum::extract::State; use ::axumrouteerror::RouteError; use ::sea_orm::DatabaseConnection;

pub async fn routegetuser( State(ref db): State, Path(username): Path ) -> Result { // If this errors, then a RouteError::new_internal_server() is returned. let user = getuserfrom_database(db, &username).await?;

Ok(user)

} ```

If the get_user_from_database function returns an error, then the handler will return a Response. The Response will have a 500 status code (for an internal error), and return the following output:

json { "error": "An unexpected error occurred" }

Different RouteError types

Let's presume get_user_from_database returns a Result<Option, Error>. We want to return a 500 if it returns an error (like above), and change the code to return a 404 if the user is not found.

```rust use ::axum::extract::State; use ::axumrouteerror::RouteError; use ::sea_orm::DatabaseConnection;

pub async fn routegetuser( State(ref db): State, Path(username): Path ) -> Result { let user = getuserfromdatabase(db, &username).await? // This additional line will return a 404 if the user is not found. .okorelse(|| RouteError::newnot_found())?;

Ok(user)

} ```

If the user is not found (get_user_from_database returns None), then this will return a 404 Response with the following JSON:

json { "error": "The resource was not found" }

Adding additional error data

Next let's add extra information to the error. Something more than just an error message.

This can be done by making a new type that serializes using Serde, and then adding this to the RouteError.

```rust use ::axum::extract::State; use ::axumrouteerror::RouteError; use ::sea_orm::DatabaseConnection; use ::serde::Deserialize; use ::serde::Serialize;

// The additional error information needs to derive these three traits.

[derive(Deserialize, Serialize, Debug)]

pub struct UserErrorInformation { pub username: String }

pub async fn routegetuser( State(ref db): State, Path(username): Path // The RouteError needs the additional data marked here ) -> Result> { let user = getuserfromdatabase(db, &username).await? .okorelse(move || { // Then you can add the data through method chaining RouteError::newnotfound() .seterror_data(UserErrorInformation { username, }) })?;

Ok(user)

} ```

If the user is not found (get_user_from_database returns None), then this will return a 404 Response with the following JSON:

json { "error": "The resource was not found", "username": "<the-username>" }