Error handling with thiserror and anyhow

Cargo.lock

@@ -60,6 +60,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "anyhow"
+version = "1.0.99"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b0674a1ddeecb70197781e945de4b3b8ffb61fa939a5597bcf48503737663100"
+
 [[package]]
 name = "arraydeque"
 version = "0.5.1"
@@ -3377,6 +3383,7 @@ dependencies = [
 name = "zero2prod"
 version = "0.1.0"
 dependencies = [
+ "anyhow",
  "axum",
  "chrono",
  "claims",
@@ -3393,6 +3400,7 @@ dependencies = [
  "serde-aux",
  "serde_json",
  "sqlx",
+ "thiserror",
  "tokio",
  "tower-http",
  "tracing",

Cargo.toml

@@ -11,6 +11,7 @@ path = "src/main.rs"
 name = "zero2prod"
 
 [dependencies]
+anyhow = "1.0.99"
 axum = "0.8.4"
 chrono = { version = "0.4.41", default-features = false, features = ["clock"] }
 config = "0.15.14"
@@ -20,6 +21,7 @@ secrecy = { version = "0.10.3", features = ["serde"] }
 serde = { version = "1.0.219", features = ["derive"] }
 serde-aux = "4.7.0"
 sqlx = { version = "0.8.6", features = ["runtime-tokio-rustls", "macros", "postgres", "uuid", "chrono", "migrate"] }
+thiserror = "2.0.16"
 tokio = { version = "1.47.1", features = ["macros", "rt-multi-thread"] }
 tower-http = { version = "0.6.6", features = ["trace"] }
 tracing = "0.1.41"

src/routes/subscriptions.rs

@@ -3,7 +3,13 @@ use crate::{
     email_client::EmailClient,
     startup::AppState,
 };
-use axum::{Form, extract::State, http::StatusCode, response::IntoResponse};
+use anyhow::Context;
+use axum::{
+    Form, Json,
+    extract::State,
+    http::StatusCode,
+    response::{IntoResponse, Response},
+};
 use chrono::Utc;
 use rand::{Rng, distr::Alphanumeric};
 use serde::Deserialize;
@@ -18,6 +24,69 @@ fn generate_subscription_token() -> String {
         .collect()
 }
 
+fn error_chain_fmt(e: &impl std::error::Error, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+    writeln!(f, "{}", e)?;
+    let mut current = e.source();
+    while let Some(cause) = current {
+        write!(f, "Caused by:\n\t{}", cause)?;
+        current = cause.source();
+        if current.is_some() {
+            writeln!(f)?;
+        }
+    }
+    Ok(())
+}
+
+// #[derive(thiserror::Error)]
+// pub enum SubscribeError {
+//     #[error("Failed to store the confirmation token for a new subscriber.")]
+//     StoreToken(#[from] StoreTokenError),
+//     #[error("A database error occured.")]
+//     Database(#[from] sqlx::Error),
+//     #[error("Failed to send a confirmation email.")]
+//     SendEmail(#[from] reqwest::Error),
+//     #[error("{0}")]
+//     Validation(String),
+// }
+
+#[derive(thiserror::Error)]
+pub enum SubscribeError {
+    #[error(transparent)]
+    UnexpectedError(#[from] anyhow::Error),
+    #[error("{0}")]
+    Validation(String),
+}
+
+impl std::fmt::Debug for SubscribeError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        error_chain_fmt(self, f)
+    }
+}
+
+impl IntoResponse for SubscribeError {
+    fn into_response(self) -> Response {
+        #[derive(serde::Serialize)]
+        struct ErrorResponse<'a> {
+            message: &'a str,
+        }
+
+        tracing::error!("{:?}", self);
+
+        // let status = match self {
+        //     SubscribeError::StoreToken(_)
+        //     | SubscribeError::Database(_)
+        //     | SubscribeError::SendEmail(_) => StatusCode::INTERNAL_SERVER_ERROR,
+        //     SubscribeError::Validation(_) => StatusCode::BAD_REQUEST,
+        // };
+        let status = match self {
+            SubscribeError::UnexpectedError(_) => StatusCode::INTERNAL_SERVER_ERROR,
+            SubscribeError::Validation(_) => StatusCode::BAD_REQUEST,
+        };
+        let message = "An internal server error occured.";
+        (status, Json(ErrorResponse { message })).into_response()
+    }
+}
+
 #[tracing::instrument(
     name = "Adding a new subscriber",
     skip(connection_pool, email_client, base_url, form),
@@ -33,39 +102,32 @@ pub async fn subscribe(
         base_url,
     }): State<AppState>,
     Form(form): Form<FormData>,
-) -> impl IntoResponse {
-    let Ok(mut transaction) = connection_pool.begin().await else {
-        return StatusCode::INTERNAL_SERVER_ERROR;
-    };
-    let Ok(new_subscriber) = form.try_into() else {
-        return StatusCode::BAD_REQUEST;
-    };
-    let Ok(subscriber_id) = insert_subscriber(&mut transaction, &new_subscriber).await else {
-        return StatusCode::INTERNAL_SERVER_ERROR;
-    };
-    let subscription_token = generate_subscription_token();
-    if store_token(&mut transaction, &subscription_token, &subscriber_id)
+) -> Result<Response, SubscribeError> {
+    let mut transaction = connection_pool
+        .begin()
         .await
-        .is_err()
-    {
-        return StatusCode::INTERNAL_SERVER_ERROR;
-    }
-    if let Err(e) = send_confirmation_email(
+        .context("Failed to acquire a Postgres connection from the pool.")?;
+    let new_subscriber = form.try_into().map_err(SubscribeError::Validation)?;
+    let subscriber_id = insert_subscriber(&mut transaction, &new_subscriber)
+        .await
+        .context("Failed to insert new subscriber in the database.")?;
+    let subscription_token = generate_subscription_token();
+    store_token(&mut transaction, &subscription_token, &subscriber_id)
+        .await
+        .context("Failed to store the confirmation token for a new subscriber.")?;
+    send_confirmation_email(
         &email_client,
         &new_subscriber,
         &base_url,
         &subscription_token,
     )
     .await
-    {
-        tracing::error!("Could not send confirmation email: {:?}", e);
-        return StatusCode::INTERNAL_SERVER_ERROR;
-    }
-    if let Err(e) = transaction.commit().await {
-        tracing::error!("Failed to commit transaction: {:?}", e);
-        return StatusCode::INTERNAL_SERVER_ERROR;
-    }
-    StatusCode::OK
+    .context("Failed to send a confirmation email.")?;
+    transaction
+        .commit()
+        .await
+        .context("Failed to commit the database transaction to store a new subscriber.")?;
+    Ok(StatusCode::OK.into_response())
 }
 
 #[tracing::instrument(
@@ -87,10 +149,7 @@ pub async fn insert_subscriber(
         new_subscriber.name.as_ref(),
         Utc::now()
     );
-    transaction.execute(query).await.map_err(|e| {
-        tracing::error!("Failed to execute query: {:?}", e);
-        e
-    })?;
+    transaction.execute(query).await?;
     Ok(subscriber_id)
 }
 
@@ -111,10 +170,7 @@ async fn store_token(
         subscription_token,
         subscriber_id,
     );
-    transaction.execute(query).await.map_err(|e| {
-        tracing::error!("Failed to execute query: {:?}", e);
-        e
-    })?;
+    transaction.execute(query).await?;
     Ok(())
 }
 

src/startup.rs

@@ -62,7 +62,8 @@ pub fn app(connection_pool: PgPool, email_client: EmailClient, base_url: String)
         .route("/subscriptions", post(subscribe))
         .route("/subscriptions/confirm", get(confirm))
         .layer(
-            TraceLayer::new_for_http().make_span_with(|request: &Request<_>| {
+            TraceLayer::new_for_http()
+                .make_span_with(|request: &Request<_>| {
                     let matched_path = request
                         .extensions()
                         .get::<MatchedPath>()
@@ -76,7 +77,8 @@ pub fn app(connection_pool: PgPool, email_client: EmailClient, base_url: String)
                         request_id,
                         some_other_field = tracing::field::Empty,
                     )
-            }),
+                })
+                .on_failure(()),
         )
         .with_state(app_state)
 }

tests/api/subscriptions.rs

@@ -122,3 +122,19 @@ async fn subscribe_sends_a_confirmation_email_with_a_link() {
     let confirmation_links = app.get_confirmation_links(email_request);
     assert_eq!(confirmation_links.html, confirmation_links.text);
 }
+
+#[tokio::test]
+async fn subscribe_fails_if_there_is_a_fatal_database_error() {
+    let app = TestApp::spawn().await;
+
+    let body = "name=Alphonse&email=alphonse.paix%40outlook.com";
+
+    sqlx::query!("ALTER TABLE subscriptions DROP COLUMN email")
+        .execute(&app.connection_pool)
+        .await
+        .unwrap();
+
+    let response = app.post_subscriptions(body.into()).await;
+
+    assert_eq!(response.status().as_u16(), 500);
+}