2021-06-19 12:34:42 +02:00
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//! Example showing how to convert errors into responses and how one might do
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//! dependency injection using trait objects.
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2021-08-02 23:09:09 +02:00
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//!
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//! Run with
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//!
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//! ```not_rust
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//! cargo run --example error_handling_and_dependency_injection
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//! ```
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2021-06-19 12:34:42 +02:00
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#![allow(dead_code)]
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2021-07-09 21:36:14 +02:00
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use axum::{
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2021-06-19 12:34:42 +02:00
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async_trait,
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extract::{Extension, Json, UrlParams},
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prelude::*,
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response::IntoResponse,
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AddExtensionLayer,
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};
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use http::StatusCode;
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use serde::{Deserialize, Serialize};
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use serde_json::json;
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use std::{net::SocketAddr, sync::Arc};
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use uuid::Uuid;
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#[tokio::main]
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async fn main() {
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2021-08-01 22:01:33 +02:00
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tracing_subscriber::fmt::init();
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2021-06-19 12:34:42 +02:00
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// Inject a `UserRepo` into our handlers via a trait object. This could be
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// the live implementation or just a mock for testing.
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let user_repo = Arc::new(ExampleUserRepo) as DynUserRepo;
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// Build our application with some routes
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let app = route("/users/:id", get(users_show))
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.route("/users", post(users_create))
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// Add our `user_repo` to all request's extensions so handlers can access
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// it.
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2021-06-19 14:06:49 +02:00
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.layer(AddExtensionLayer::new(user_repo));
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2021-06-19 12:34:42 +02:00
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// Run our application
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let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
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tracing::debug!("listening on {}", addr);
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2021-08-04 15:38:51 +02:00
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axum::Server::bind(&addr)
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2021-06-19 12:50:33 +02:00
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.serve(app.into_make_service())
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.await
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.unwrap();
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2021-06-19 12:34:42 +02:00
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}
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/// Handler for `GET /users/:id`.
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///
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/// Extracts the user repo from request extensions and calls it. `UserRepoError`s
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/// are automatically converted into `AppError` which implements `IntoResponse`
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/// so it can be returned from handlers directly.
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async fn users_show(
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UrlParams((user_id,)): UrlParams<(Uuid,)>,
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Extension(user_repo): Extension<DynUserRepo>,
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) -> Result<response::Json<User>, AppError> {
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let user = user_repo.find(user_id).await?;
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Ok(user.into())
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}
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/// Handler for `POST /users`.
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async fn users_create(
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Json(params): Json<CreateUser>,
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Extension(user_repo): Extension<DynUserRepo>,
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) -> Result<response::Json<User>, AppError> {
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let user = user_repo.create(params).await?;
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Ok(user.into())
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}
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/// Our app's top level error type.
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enum AppError {
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/// Something went wrong when calling the user repo.
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UserRepo(UserRepoError),
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}
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/// This makes it possible to use `?` to automatically convert a `UserRepoError`
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/// into an `AppError`.
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impl From<UserRepoError> for AppError {
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fn from(inner: UserRepoError) -> Self {
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AppError::UserRepo(inner)
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}
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}
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impl IntoResponse for AppError {
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fn into_response(self) -> http::Response<Body> {
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let (status, error_json) = match self {
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AppError::UserRepo(UserRepoError::NotFound) => {
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(StatusCode::NOT_FOUND, json!("User not found"))
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}
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AppError::UserRepo(UserRepoError::InvalidUsername) => {
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(StatusCode::UNPROCESSABLE_ENTITY, json!("Invalid username"))
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}
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};
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let mut response = response::Json(json!({
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"error": error_json,
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}))
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.into_response();
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*response.status_mut() = status;
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response
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}
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}
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/// Example implementation of `UserRepo`.
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struct ExampleUserRepo;
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#[async_trait]
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impl UserRepo for ExampleUserRepo {
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async fn find(&self, _user_id: Uuid) -> Result<User, UserRepoError> {
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unimplemented!()
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}
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async fn create(&self, _params: CreateUser) -> Result<User, UserRepoError> {
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unimplemented!()
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}
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}
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/// Type alias that makes it easier to extract `UserRepo` trait objects.
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type DynUserRepo = Arc<dyn UserRepo + Send + Sync>;
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/// A trait that defines things a user repo might support.
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#[async_trait]
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trait UserRepo {
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/// Loop up a user by their id.
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async fn find(&self, user_id: Uuid) -> Result<User, UserRepoError>;
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/// Create a new user.
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async fn create(&self, params: CreateUser) -> Result<User, UserRepoError>;
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}
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#[derive(Debug, Serialize)]
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struct User {
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id: Uuid,
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username: String,
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}
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#[derive(Debug, Deserialize)]
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struct CreateUser {
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username: String,
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}
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/// Errors that can happen when using the user repo.
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#[derive(Debug)]
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enum UserRepoError {
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NotFound,
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InvalidUsername,
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}
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