feat(extract::Path): add ErrorKind::DeserializeError to specialize Er…

…rorKind::Message

This commit introduces another `extract::path::ErrorKind` variant that captures the
serde error nominally captured through the `serde::de::Error` trait impl on `PathDeserializeError`.
We augment the deserialization error with the captured (key, value), allowing `extract::Path`, and wrapping
extractors, to gain programmatic access to the key name, and attempted deserialized value.

The `PathDeserializationError::custom` is used two places in addition to capture the deserialization error.
These usages should still be unaffected.

axum/src/extract/path/de.rs

@@ -94,7 +94,20 @@ impl<'de> Deserializer<'de> for PathDeserializer<'de> {
                 .got(self.url_params.len())
                 .expected(1));
         }
-        visitor.visit_borrowed_str(&self.url_params[0].1)
+        let key = &self.url_params[0].0;
+        let value = &self.url_params[0].1;
+        visitor
+            .visit_borrowed_str(value)
+            .map_err(|e: Self::Error| match e.kind {
+                ErrorKind::Message(message) => {
+                    PathDeserializationError::new(ErrorKind::DeserializeError {
+                        key: key.to_string(),
+                        value: value.as_str().to_owned(),
+                        message,
+                    })
+                }
+                kind => PathDeserializationError::new(kind),
+            })
     }
 
     fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
@@ -362,7 +375,18 @@ impl<'de> Deserializer<'de> for ValueDeserializer<'de> {
     where
         V: Visitor<'de>,
     {
-        visitor.visit_borrowed_str(self.value)
+        visitor
+            .visit_borrowed_str(self.value)
+            .map_err(|e: Self::Error| match e.kind {
+                ErrorKind::Message(message) => {
+                    PathDeserializationError::new(ErrorKind::DeserializeError {
+                        key: self.key.map(|k| k.key().to_owned()).unwrap_or_default(),
+                        value: self.value.as_str().to_owned(),
+                        message,
+                    })
+                }
+                kind => PathDeserializationError::new(kind),
+            })
     }
 
     fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, Self::Error>
@@ -608,6 +632,15 @@ enum KeyOrIdx<'de> {
     Idx { idx: usize, key: &'de str },
 }
 
+impl<'de> KeyOrIdx<'de> {
+    fn key(&self) -> &'de str {
+        match &self {
+            Self::Key(key) => key,
+            Self::Idx { key, .. } => key,
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -928,4 +961,18 @@ mod tests {
             }
         );
     }
+
+    #[test]
+    fn test_deserialize_key_value() {
+        test_parse_error!(
+            vec![("id", "123123-123-123123")],
+            uuid::Uuid,
+            ErrorKind::DeserializeError {
+                key: "id".to_string(),
+                value: "123123-123-123123".to_string(),
+                message: "UUID parsing failed: invalid group count: expected 5, found 3"
+                    .to_string(),
+            }
+        );
+    }
 }

axum/src/extract/path/mod.rs

@@ -305,6 +305,16 @@ pub enum ErrorKind {
         name: &'static str,
     },
 
+    /// Failed to deserialize the value with a custom deserialization error.
+    DeserializeError {
+        /// The key at which the invalid value was located.
+        key: String,
+        /// The value that failed to deserialize.
+        value: String,
+        /// The deserializaation failure message.
+        message: String,
+    },
+
     /// Catch-all variant for errors that don't fit any other variant.
     Message(String),
 }
@@ -347,6 +357,11 @@ impl fmt::Display for ErrorKind {
                 f,
                 "Cannot parse value at index {index} with value `{value:?}` to a `{expected_type}`"
             ),
+            ErrorKind::DeserializeError {
+                key,
+                value,
+                message,
+            } => write!(f, "Cannot parse `{key}` with value `{value:?}`: {message}"),
         }
     }
 }
@@ -371,6 +386,7 @@ impl FailedToDeserializePathParams {
     pub fn body_text(&self) -> String {
         match self.0.kind {
             ErrorKind::Message(_)
+            | ErrorKind::DeserializeError { .. }
             | ErrorKind::InvalidUtf8InPathParam { .. }
             | ErrorKind::ParseError { .. }
             | ErrorKind::ParseErrorAtIndex { .. }
@@ -385,6 +401,7 @@ impl FailedToDeserializePathParams {
     pub fn status(&self) -> StatusCode {
         match self.0.kind {
             ErrorKind::Message(_)
+            | ErrorKind::DeserializeError { .. }
             | ErrorKind::InvalidUtf8InPathParam { .. }
             | ErrorKind::ParseError { .. }
             | ErrorKind::ParseErrorAtIndex { .. }
@@ -887,4 +904,43 @@ mod tests {
         let body = res.text().await;
         assert_eq!(body, "a=foo b=bar c=baz");
     }
+
+    #[crate::test]
+    async fn deserialize_error_single_value() {
+        let app = Router::new().route(
+            "/resources/:res",
+            get(|res: Path<uuid::Uuid>| async move {
+                let _res = res;
+            }),
+        );
+
+        let client = TestClient::new(app);
+        let res = client.get("/resources/123123-123-123123").await;
+        let body = res.text().await;
+        assert_eq!(
+            body,
+            r#"Invalid URL: Cannot parse `res` with value `"123123-123-123123"`: UUID parsing failed: invalid group count: expected 5, found 3"#
+        );
+    }
+
+    #[crate::test]
+    async fn deserialize_error_multi_value() {
+        let app = Router::new().route(
+            "/resources/:res/sub/:sub",
+            get(
+                |Path((res, sub)): Path<(uuid::Uuid, uuid::Uuid)>| async move {
+                    let _res = res;
+                    let _sub = sub;
+                },
+            ),
+        );
+
+        let client = TestClient::new(app);
+        let res = client.get("/resources/456456-123-456456/sub/123").await;
+        let body = res.text().await;
+        assert_eq!(
+            body,
+            r#"Invalid URL: Cannot parse `res` with value `"456456-123-456456"`: UUID parsing failed: invalid group count: expected 5, found 3"#
+        );
+    }
 }