examples(error-handling): derive_from_request

examples/error-handling/Cargo.toml

@@ -8,6 +8,7 @@ edition = "2021"
 [dependencies]
 axum = { path = "../../axum", features=["matched-path"] }
 axum-extra = { path = "../../axum-extra" }
+axum-macros = { path = "../../axum-macros" }
 chrono = { version = "0.4", features = ["serde"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"

examples/error-handling/src/derive_from_request.rs

@@ -0,0 +1,46 @@
+use axum::{extract::rejection::JsonRejection, http::StatusCode, response::IntoResponse};
+use axum_macros::FromRequest;
+use chrono::Utc;
+use serde_json::{json, Value};
+
+pub async fn handler(Json(value): Json<Value>) -> impl IntoResponse {
+    Json(dbg!(value));
+}
+
+// create an extractor that internally uses `axum::Json` but has a custom rejection
+#[derive(FromRequest)]
+#[from_request(via(axum::Json), rejection(ApiError))]
+pub struct Json<T>(T);
+
+#[derive(Debug)]
+pub struct ApiError {
+    code: StatusCode,
+    message: String,
+}
+
+impl From<JsonRejection> for ApiError {
+    fn from(rejection: JsonRejection) -> Self {
+        let code = match rejection {
+            JsonRejection::JsonDataError(_) | JsonRejection::MissingJsonContentType(_) => {
+                StatusCode::BAD_REQUEST
+            }
+            _ => StatusCode::INTERNAL_SERVER_ERROR,
+        };
+        Self {
+            code,
+            message: rejection.to_string(),
+        }
+    }
+}
+
+impl IntoResponse for ApiError {
+    fn into_response(self) -> axum::response::Response {
+        let payload = json!({
+            "message": self.message,
+            "timestamp": Utc::now(),
+            "origin": "derive_from_request"
+        });
+
+        (self.code, axum::Json(payload)).into_response()
+    }
+}

examples/error-handling/src/main.rs

@@ -1,5 +1,6 @@
-mod with_rejection;
 mod custom_extractor;
+mod derive_from_request;
+mod with_rejection;
 
 use axum::{routing::get, Router, Server};
 use std::net::SocketAddr;
@@ -17,7 +18,8 @@ async fn main() {
     // Build our application with some routes
     let app = Router::new()
         .route("/withRejection", get(with_rejection::handler))
-        .route("/customExtractor", get(custom_extractor::handler));
+        .route("/customExtractor", get(custom_extractor::handler))
+        .route("/deriveFromRequest", get(derive_from_request::handler));
 
     // Run our application
     let addr = SocketAddr::from(([127, 0, 0, 1], 3000));