Is the Thrift serialization compatible both directions?

[Jean Rodier]

Hi,

Is this statement true, especially the last part?  (from: 
https://diwakergupta.github.io/thrift-missing-guide/)

Any new fields that you add should be optional. This means that any messages 
serialized by code using your "old" message format can be parsed by your new 
generated code, as they won’t be missing any required elements. Similarly, 
messages created by your new code can be parsed by your old code: old binaries 
simply ignore the new field when parsing. However, the unknown fields are not 
discarded, and if the message is later serialized, the unknown fields are 
serialized along with it — so if the message is passed on to new code, the new 
fields are still available.

I tested is using the following files in C++ and apparently it is not…

File msg1.thrift
--------------------
namespace cpp msg1
struct msgStruct {
    1:                        i32 version,
    2:                        i64 time
}

File msg2.thrift
--------------------
namespace cpp msg2
struct msgStruct {
    1:                        i32 version,
    2:                        i64 time,
    3: optional i32 flag
}

File main.cpp
------------------
/*
Build commands:
   thrift --gen cpp msg1.thrift
   thrift --gen cpp msg2.thrift

   g++ main.cpp -o test -lthrift -lthriftz
*/

#include <vector>
using namespace std;

#include <thrift/Thrift.h>
#include <thrift/protocol/TProtocol.h>
#include <thrift/protocol/TCompactProtocol.h>
#include <thrift/protocol/TJSONProtocol.h>
#include <thrift/transport/TTransport.h>

#include "gen-cpp/msg1_types.h"      // Thrift generated
#include "gen-cpp/msg2_types.h"      // Thrift generated

template<typename T>
void serialize(const T & obj, vector<uint8_t> & s) {
   ::boost::shared_ptr<apache::thrift::transport::TMemoryBuffer> buffer(new 
apache::thrift::transport::TMemoryBuffer());
   //::boost::shared_ptr<apache::thrift::protocol::TCompactProtocol> 
protocol(new apache::thrift::protocol::TCompactProtocol(buffer));
   ::boost::shared_ptr<apache::thrift::protocol::TJSONProtocol> protocol(new 
apache::thrift::protocol::TJSONProtocol(buffer));

   obj.write(protocol.get());

   uint8_t * buf;
   uint32_t sz;

   buffer.get()->getBuffer(&buf, &sz);
   s.resize(sz);
   s.assign(buf, buf + sz);
}

template<typename T>
void deserialize(const vector<uint8_t> & s, T & obj) {
   ::boost::shared_ptr<apache::thrift::transport::TMemoryBuffer> buffer(new 
apache::thrift::transport::TMemoryBuffer((uint8_t*)s.data(), s.size()));
   //::boost::shared_ptr<apache::thrift::protocol::TCompactProtocol> 
protocol(new apache::thrift::protocol::TCompactProtocol(buffer));
   ::boost::shared_ptr<apache::thrift::protocol::TJSONProtocol> protocol(new 
apache::thrift::protocol::TJSONProtocol(buffer));

   obj.read(protocol.get());
}

int main(int argc, char** argv) {
   msg2::msgStruct m2;
   m2.__set_version(123);
  m2.__set_time(456);
   m2.__set_flag(789);

   vector<uint8_t> buf;
   serialize<msg2::msgStruct>(m2, buf);

   string output(buf.begin(), buf.end());
   cout << output << endl;
   // {"1":{"i32":123},"2":{"i64":456},"3":{"i32":789}}

   msg1::msgStruct m1;
   deserialize<msg1::msgStruct>(buf, m1);

   vector<uint8_t> buf2;
   serialize<msg1::msgStruct>(m1, buf2);

   string output2(buf2.begin(), buf2.end());
   cout << output2 << endl;
   // {"1":{"i32":123},"2":{"i64":456}} expecting 
{"1":{"i32":123},"2":{"i64":456},"3":{"i32":789}}

   msg2::msgStruct m2_2;
   deserialize<msg2::msgStruct>(buf2, m2_2);

   vector<uint8_t> buf3;
   serialize<msg2::msgStruct>(m2_2, buf3);

   string output3(buf3.begin(), buf3.end());
   cout << output3 << endl;
   // {"1":{"i32":123},"2":{"i64":456}} expecting 
{"1":{"i32":123},"2":{"i64":456},"3":{"i32":789}}
}

#include "gen-cpp/msg1_types.cpp"      // Thrift generated
#include "gen-cpp/msg1_constants.cpp"  // Thrift generated
#include "gen-cpp/msg2_types.cpp"      // Thrift generated
#include "gen-cpp/msg2_constants.cpp"  // Thrift generated