Implement OptionalFromRequest for the Json extractor (#3142)

axum/CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 # Unreleased
 
+- **added:** Implement `OptionalFromRequest` for `Json` ([#3142])
+
+[#3142]: https://github.com/tokio-rs/axum/pull/3142
+
 # 0.8.0
 
 ## since rc.1

axum/src/json.rs

@@ -1,5 +1,6 @@
 use crate::extract::Request;
 use crate::extract::{rejection::*, FromRequest};
+use axum_core::extract::OptionalFromRequest;
 use axum_core::response::{IntoResponse, Response};
 use bytes::{BufMut, Bytes, BytesMut};
 use http::{
@@ -112,6 +113,28 @@ where
     }
 }
 
+impl<T, S> OptionalFromRequest<S> for Json<T>
+where
+    T: DeserializeOwned,
+    S: Send + Sync,
+{
+    type Rejection = JsonRejection;
+
+    async fn from_request(req: Request, state: &S) -> Result<Option<Self>, Self::Rejection> {
+        let headers = req.headers();
+        if headers.get(header::CONTENT_TYPE).is_some() {
+            if json_content_type(headers) {
+                let bytes = Bytes::from_request(req, state).await?;
+                Ok(Some(Self::from_bytes(&bytes)?))
+            } else {
+                Err(MissingJsonContentType.into())
+            }
+        } else {
+            Ok(None)
+        }
+    }
+}
+
 fn json_content_type(headers: &HeaderMap) -> bool {
     let content_type = if let Some(content_type) = headers.get(header::CONTENT_TYPE) {
         content_type