Check whether a parsed Protocol Buffers (Protobuf) proto3 message is valid - c++

Question

I currently need to transfer a Protobuf message of a given type Foo over the network and handle it on reception.
I am using Protobuf 3.5.1 and the proto3 language.
On reception I do the following:
Create an empty instance of the expected type Foo (via a Factory Method, since it may change).
Parse the message from a CodedInputStream (constructed from the data received from the network).
Validate whether the parsing has been successful.
Here is a minimal code snippet illustrating the concrete problem:
// Create the empty Protobuf message of the EXPECTED type.
std::shared_ptr<google::protobuf::Message> message = std::make_unique<Foo>();
// Create the CodedInputStream from the network data.
google::protobuf::io::CodedInputStream stream{receive_buffer_.data(), static_cast<int>(bytes_transferred)};
if (message->ParseFromCodedStream(&stream) && stream.ConsumedEntireMessage() && message->IsInitialized()) {
// Message is of correct type and correctly parsed.
} else {
// Message is NOT VALID.
// TODO: This does not work if sending a message of type `Bar`.
}
Everything works flawless if the sender transfers messages of the expected type Foo, but things get weird if sending a message of another type Bar.
Both messages have a similar structure (they only difference is the oneof type which uses different types (but may use identical field identity values):
message Foo {
First first = 1;
oneof second {
A a = 2;
B b = 3;
}
}
message Bar {
First first = 1;
oneof second {
C c = 2;
D d = 3;
}
}
I haven't found a way yet, that detects whether the received Protobuf message type is "valid".
So my question is: How can I safely detect whether the parsed instance of Foo is valid and it is not an instance of another (similarly structured but completely different) Protobuf message type? Do I need to manually add the name of the message sent as a field (that would be stupid, but should work)?