Automated Code Change

pybind11_protobuf/check_unknown_fields.cc

@@ -95,18 +95,24 @@ bool HasUnknownFields::FindUnknownFieldsRecursive(
     const ::google::protobuf::Message* sub_message, uint32_t depth) {
   const ::google::protobuf::Reflection& reflection = *sub_message->GetReflection();
 
-  // If there are unknown fields, stop searching.
+  // Check if any unknown fields on this message correspond to extensions that
+  // are known by Python's descriptor pool (i.e., Python imported the extension,
+  // but C++ did not link the corresponding cc_proto_library).
+  // Iterate through all unknown fields, as earlier entries might be unknown
+  // regular fields or extensions not registered in Python.
   const ::google::protobuf::UnknownFieldSet& unknown_field_set =
       reflection.GetUnknownFields(*sub_message);
   if (!unknown_field_set.empty()) {
     unknown_field_parent_descriptor = sub_message->GetDescriptor();
-    unknown_field_number = unknown_field_set.field(0).number();
-
-    // Stop only if the extension is known by Python.
-    if (py_proto_api->GetDefaultDescriptorPool()->FindExtensionByNumber(
-            unknown_field_parent_descriptor, unknown_field_number)) {
-      field_fqn_parts.resize(depth);
-      return true;
+    for (int i = 0; i < unknown_field_set.field_count(); ++i) {
+      int field_num = unknown_field_set.field(i).number();
+      // Stop and report as soon as an extension known by Python is found.
+      if (py_proto_api->GetDefaultDescriptorPool()->FindExtensionByNumber(
+              unknown_field_parent_descriptor, field_num)) {
+        unknown_field_number = field_num;
+        field_fqn_parts.resize(depth);
+        return true;
+      }
     }
   }
 

pybind11_protobuf/tests/extension_module.cc

@@ -69,6 +69,15 @@ PYBIND11_MODULE(extension_module, m) {
       [](const BaseMessage& inout) -> const BaseMessage& { return inout; },
       py::arg("message"), py::return_value_policy::copy);
 
+  m.def(
+      "parse_base_message_from_bytes",
+      [](const py::bytes& bytes) -> BaseMessage {
+        BaseMessage msg;
+        msg.ParseFromString(bytes);
+        return msg;
+      },
+      py::arg("bytes"));
+
   DefReserialize<BaseMessage>(m, "reserialize_base_message");
   DefReserialize<pybind11::test::NestLevel2>(m, "reserialize_nest_level2");
   DefReserialize<pybind11::test::NestRepeated>(m, "reserialize_nest_repeated");

pybind11_protobuf/tests/extension_test.py

@@ -213,5 +213,44 @@ def test_reserialize_allow_python_unknown_fields(self):
     b = m.reserialize_base_message(a)
     self.assertEqual(a.SerializeToString(), b.SerializeToString())
 
+  def test_reserialize_multiple_unknown_fields(self):
+    # Concatenating two serialized messages places their fields into the wire
+    # stream in sequential order:
+    # 1. 'inner' contains field 2001 (AllowUnknownInnerExtension.hook), which is
+    #    unknown to both C++ and Python for BaseMessage.
+    # 2. 'msg_with_ext' contains field 1003 (MessageInOtherFile extension),
+    #    which is unknown to C++ (unlinked cc_proto_library), but is known to
+    #    Python's descriptor pool.
+    # When BaseMessage parses raw_data in C++, its UnknownFieldSet preserves
+    # this order: field(0) = 2001, field(1) = 1003.
+    inner = get_allow_unknown_inner(63)
+    msg_with_ext = get_py_message(in_other_file_value=63)
+    raw_data = inner.SerializeToString() + msg_with_ext.SerializeToString()
+
+    # When unknown_field_exception_is_expected() is True (e.g., in fast_cpp
+    # mode with unknown fields disallowed), pybind11_protobuf scans
+    # UnknownFieldSet and raises ValueError upon detecting field 1003.
+    # Otherwise (e.g., pure Python / upb or allowed mode), it falls back to
+    # serialization, allowing Python to read the extension losslessly.
+    if unknown_field_exception_is_expected():
+      with self.assertRaises(ValueError) as ctx:
+        m.parse_base_message_from_bytes(raw_data)
+      self.assertStartsWith(
+          str(ctx.exception),
+          'Proto Message of type pybind11.test.BaseMessage has an'
+          ' Unknown Field: 1003 (')
+      self.assertEndsWith(
+          str(ctx.exception),
+          'extension.proto). Please add the required `cc_proto_library` `deps`.'
+          ' Only if there is no alternative to suppressing this error, use'
+          ' `pybind11_protobuf::AllowUnknownFieldsFor('
+          '"pybind11.test.BaseMessage", "");`'
+          ' (Warning: suppressions may mask critical bugs.)')
+    else:
+      b = m.parse_base_message_from_bytes(raw_data)
+      b_value = b.Extensions[extension_in_other_file_pb2.MessageInOtherFile
+                             .message_in_other_file_extension].value
+      self.assertEqual(63, b_value)
+
 if __name__ == '__main__':
   absltest.main()