reflect: require slash-delimited Any type URLs

.changes/unreleased/fixed-20261003-211406.yaml

@@ -0,0 +1,3 @@
+kind: Fixed
+body: Reject reflective Any type URLs without a slash-delimited message name when unpacking or converting to and from JSON.
+time: 2026-10-03T21:14:06.552245+02:00

buffa-descriptor/src/reflect/dynamic.rs

@@ -1519,8 +1519,8 @@ impl DynamicMessage {
     ///
     /// - [`AnyError::NotAny`] if this message is not a `google.protobuf.Any`.
     /// - [`AnyError::MissingTypeUrl`] if the `Any` has no `type_url`.
-    /// - [`AnyError::UnknownType`] if the `type_url` names a type the pool
-    ///   doesn't carry.
+    /// - [`AnyError::UnknownType`] if the `type_url` has no non-empty name
+    ///   after a `/`, or names a type the pool doesn't carry.
     /// - [`AnyError::Decode`] if the wrapped bytes are malformed. Note that
     ///   an `Any` whose `value` is absent or empty is **not** an error: it
     ///   decodes to a default-valued message of the resolved type, per the
@@ -1541,13 +1541,9 @@ impl DynamicMessage {
             Some(Value::Bytes(b)) => b,
             _ => &[],
         };
-        let type_name = type_url.rsplit('/').next().unwrap_or(type_url);
-        let idx = self
-            .pool
-            .message_index(type_name)
-            .ok_or_else(|| AnyError::UnknownType {
-                type_url: type_url.to_owned(),
-            })?;
+        let idx = resolve_any_type(&self.pool, type_url).ok_or_else(|| AnyError::UnknownType {
+            type_url: type_url.to_owned(),
+        })?;
         DynamicMessage::decode(Arc::clone(&self.pool), idx, value).map_err(|source| {
             AnyError::Decode {
                 type_url: type_url.to_owned(),
@@ -1633,6 +1629,15 @@ impl DynamicMessage {
 /// The fully-qualified name of `google.protobuf.Any`.
 const ANY_FULL_NAME: &str = "google.protobuf.Any";
 
+/// Resolve an Any URL whose last `/` is followed by a non-empty type name.
+pub(super) fn resolve_any_type(pool: &DescriptorPool, type_url: &str) -> Option<MessageIndex> {
+    let (_, name) = type_url.rsplit_once('/')?;
+    if name.is_empty() {
+        return None;
+    }
+    pool.message_index(name)
+}
+
 /// An error from [`DynamicMessage::unpack_any`] or
 /// [`DynamicMessage::pack_any`].
 #[derive(Clone, Debug)]
@@ -1649,7 +1654,8 @@ pub enum AnyError {
     AnyNotRegistered,
     /// The `Any` has no `type_url` (field 1 absent, empty, or not a string).
     MissingTypeUrl,
-    /// The `Any`'s `type_url` names a type the pool does not carry.
+    /// The `Any`'s `type_url` has no non-empty name after a `/`, or names a
+    /// type the pool does not carry.
     UnknownType {
         /// The unresolvable type URL.
         type_url: String,

buffa-descriptor/src/reflect/json_wkt.rs

@@ -505,7 +505,7 @@ fn serialize_any<S: Serializer>(
         // Empty Any → empty object.
         return s.serialize_map(Some(0))?.end();
     }
-    let Some(inner_idx) = resolve_any_type(pool, type_url) else {
+    let Some(inner_idx) = super::dynamic::resolve_any_type(pool, type_url) else {
         return Err(S::Error::custom(format!(
             "Any type_url {type_url:?} not registered in the descriptor pool"
         )));
@@ -577,7 +577,7 @@ fn deserialize_any<'de, D: Deserializer<'de>>(
     let Some(serde_json::Value::String(type_url)) = obj.remove("@type") else {
         return Err(D::Error::custom("Any object missing string \"@type\""));
     };
-    let Some(inner_idx) = resolve_any_type(&pool, &type_url) else {
+    let Some(inner_idx) = super::dynamic::resolve_any_type(&pool, &type_url) else {
         return Err(D::Error::custom(format!(
             "Any type_url {type_url:?} not registered in the descriptor pool"
         )));
@@ -650,14 +650,6 @@ fn deserialize_any<'de, D: Deserializer<'de>>(
     ))
 }
 
-/// Resolve a `type_url` to a [`MessageIndex`]. Accepts `type.googleapis.com/`
-/// and any other prefix; the type name is the segment after the last `/`.
-fn resolve_any_type(pool: &DescriptorPool, type_url: &str) -> Option<MessageIndex> {
-    let name = type_url.rsplit('/').next()?;
-    pool.message_index(name)
-}
-
-
 // ── Timestamp / Duration / FieldMask formatting ─────────────────────────────
 //
 // The shared formatting and parsing primitives live in

buffa-descriptor/tests/options_any_symbol_e2e.rs

@@ -132,6 +132,80 @@ fn any_json_spreads_payload_extensions() {
     assert_eq!(parsed.unpack_any().unwrap(), opts);
 }
 
+#[cfg(feature = "json")]
+#[test]
+fn empty_any_json_preserves_empty_object() {
+    let p = pool();
+    let any_idx = p.message_index("google.protobuf.Any").unwrap();
+    let any = DynamicMessage::new(Arc::clone(&p), any_idx);
+    assert_eq!(any.to_json().unwrap(), "{}");
+    for input in ["{}", r#"{"@type":""}"#] {
+        let strict = DynamicMessage::from_json(Arc::clone(&p), any_idx, input);
+        let lenient = DynamicMessage::from_json_ignoring_unknown(Arc::clone(&p), any_idx, input);
+        if input == "{}" {
+            assert_eq!(strict.unwrap(), any);
+            assert_eq!(lenient.unwrap(), any);
+        } else {
+            assert!(strict.is_err());
+            assert!(lenient.is_err());
+        }
+    }
+}
+
+#[cfg(feature = "json")]
+#[test]
+fn any_json_requires_a_slash_and_non_empty_type_name() {
+    let p = pool();
+    let any_idx = p.message_index("google.protobuf.Any").unwrap();
+
+    for type_url in [
+        "type.googleapis.com/reflect.opt.Annotated",
+        "company.example/v1/reflect.opt.Annotated",
+        "/reflect.opt.Annotated",
+    ] {
+        let input = format!(r#"{{"@type":"{type_url}"}}"#);
+        let parsed = DynamicMessage::from_json(Arc::clone(&p), any_idx, &input)
+            .unwrap_or_else(|err| panic!("{type_url}: {err}"));
+        assert_eq!(parsed.to_json().unwrap(), input);
+        assert_eq!(
+            DynamicMessage::from_json_ignoring_unknown(Arc::clone(&p), any_idx, &input)
+                .unwrap()
+                .to_json()
+                .unwrap(),
+            input
+        );
+    }
+
+    for type_url in [
+        "reflect.opt.Annotated",
+        "type.googleapis.com/",
+        "company.example/v1/reflect.opt.Annotated/",
+        "/",
+        "type.googleapis.com/no.Such",
+    ] {
+        let input = format!(r#"{{"@type":"{type_url}"}}"#);
+        assert!(
+            DynamicMessage::from_json(Arc::clone(&p), any_idx, &input).is_err(),
+            "unexpectedly parsed {type_url:?}"
+        );
+
+        assert!(
+            DynamicMessage::from_json_ignoring_unknown(Arc::clone(&p), any_idx, &input).is_err(),
+            "unexpectedly parsed {type_url:?} in lenient mode"
+        );
+
+        let mut any = DynamicMessage::new(Arc::clone(&p), any_idx);
+        any.set(
+            p.message(any_idx).field(1).unwrap(),
+            Value::String(type_url.to_owned()),
+        );
+        assert!(
+            any.to_json().is_err(),
+            "unexpectedly serialized {type_url:?}"
+        );
+    }
+}
+
 /// Read a custom option off a re-encoded options message: decode it as a
 /// `DynamicMessage` of `options_type` and pull the extension's value. This
 /// is the documented generic flow for reading a custom option by name when
@@ -224,6 +298,44 @@ fn any_pack_unpack_round_trip() {
     assert_eq!(back, ann);
 }
 
+#[test]
+fn any_unpack_requires_a_slash_and_non_empty_type_name() {
+    let p = pool();
+    let any_idx = p.message_index("google.protobuf.Any").unwrap();
+    let any_md = p.message(any_idx);
+
+    for type_url in [
+        "type.googleapis.com/reflect.opt.Annotated",
+        "company.example/v1/reflect.opt.Annotated",
+        "/reflect.opt.Annotated",
+    ] {
+        let mut any = DynamicMessage::new(Arc::clone(&p), any_idx);
+        any.set(any_md.field(1).unwrap(), Value::String(type_url.to_owned()));
+        let unpacked = any
+            .unpack_any()
+            .unwrap_or_else(|err| panic!("{type_url}: {err}"));
+        assert_eq!(
+            unpacked.message_descriptor().full_name(),
+            "reflect.opt.Annotated"
+        );
+    }
+
+    for type_url in [
+        "reflect.opt.Annotated",
+        "type.googleapis.com/",
+        "company.example/v1/reflect.opt.Annotated/",
+        "/",
+        "type.googleapis.com/no.Such",
+    ] {
+        let mut any = DynamicMessage::new(Arc::clone(&p), any_idx);
+        any.set(any_md.field(1).unwrap(), Value::String(type_url.to_owned()));
+        match any.unpack_any().unwrap_err() {
+            AnyError::UnknownType { type_url: actual } => assert_eq!(actual, type_url),
+            other => panic!("unexpected error for {type_url:?}: {other}"),
+        }
+    }
+}
+
 #[test]
 fn any_errors() {
     let p = pool();