Protobuf C++ required fields are not checked/enforced - c++

Question

I am new to Protocol Buffers and currently I see the following problem:
We use proto2 syntax with Protocol Buffers 3.2.0 library and observe that required fields are not enforced during the serialization.
Here a basic example with Catch C++ tests:
syntax = "proto2";
package simple_test;
message SimpleMessage
{
required string field1 = 1;
required string field2 = 2;
}
#include "simple.pb.h"
#include <catch.hpp>
#include <string>
SCENARIO("Verify that serialization with missing required fields fails", "[protobuf]")
{
GIVEN("a message")
{
simple_test::SimpleMessage m;
WHEN("field1 is set and field2 is not and both are required")
{
m.set_field1("aaa");
THEN("serializing this message to string buffer must fail")
{
std::string buffer;
CHECK_FALSE(m.SerializeToString(&buffer));
REQUIRE(buffer.empty());
}
}
}
}
m.SerializeToString(&buffer) returns true and buffer.empty() is false.
What I know
required fields were removed in Protobuf v3.
My Questions
Is there a setting or any kind of config switch that I can enforce these checks with Protobuf v3?
What happens with the use case:
proto2 Message compiled with Protobuf v3 compiler. This message ends up with partially filled required fields and is going to be send to Protobuf v2 enpoint which enforces the required fields. Does this effectively mean that there were just bytes sent for nothing, because the message is invalid and will be rejected?
Should I downgrade from v3.2.0 to 2.x to disallow sending of incomplete messages at client side?

Answer 1

I came along this documentation which I've overseen before:
Standard Message Methods and there is the documentation for:
Standard Message Methods
Each message class also contains a number of other methods that let you check or manipulate the entire message, including:
bool IsInitialized() const;: checks if all the required fields have been set.
This is what I needed! Protobuf are great again!

Answer 2

Is there a setting or any kind of config switch that I can enforce these checks with Protobuf v3?
Have you tried building protobuf in debug config? I think you'll find that it'll assert in this case.
What happens with the use case:
proto2 Message compiled with Protobuf v3 compiler. This message ends up with partially filled required fields and is going to be send to Protobuf v2 enpoint which enforces the required fields. Does this effectively mean that there were just bytes sent for nothing, because the message is invalid and will be rejected?
In this case, the receiver can ParsePartialFromXXX to received what was sent. He can test message validity with message.has_xxx()
Should I downgrade from v3.2.0 to 2.x to disallow sending of incomplete messages at client side?
I wouldn't. Perhaps write a checker for each message type to assert that each required field is present. Better yet, think about it the proto3 way and treat a missing field as a default value in the receiver. The protobuf documentation advises never adding required fields to an existing message type and suggests 'thinking very carefully' before making fields required. You could take this to mean 'oops, the concept of required fields was an error'.