Apache Thrift: Returning a list/container

Question

I made a simple thrift file like this:

thrifttest.thrift

namespace cpp thrifttest
namespace d thrifttest
namespace java thrifttest
namespace php thrifttest
namespace perl thrifttest

service Test {

    list<i64> ping();

}

and in shell ran "thrift --gen cpp thrifttest.thrift"

However, when I looked at gen-cpp/Test_server.skeleton.cpp it made the i64 list a parameter, not a return type:

Test_server.skeleton.cpp (excerpt)

void ping(std::vector<int64_t> & _return) {
    // Your implementation goes here
    printf("ping\n");
}

and in my server.cpp program, after I make a function ping() that returns an "std::vector &", the compiler complains that

error: cannot allocate an object of abstract type ‘TestHandler’ server.cpp:30:7: note: because the following virtual functions are pure within ‘TestHandler’:

this is the full code for server.cpp server.cpp

#include <thrift/concurrency/ThreadManager.h>
#include <thrift/concurrency/PosixThreadFactory.h>
#include <thrift/protocol/TBinaryProtocol.h>
#include <thrift/server/TSimpleServer.h>
#include <thrift/server/TThreadPoolServer.h>
#include <thrift/server/TThreadedServer.h>
#include <thrift/transport/TServerSocket.h>
#include <thrift/transport/TTransportUtils.h>

#include <iostream>
#include <stdexcept>
#include <sstream>

#include "gen-cpp/Test.h"

using namespace std;
using namespace apache::thrift;
using namespace apache::thrift::protocol;
using namespace apache::thrift::transport;
using namespace apache::thrift::server;

using boost::shared_ptr;

using namespace thrifttest;

using namespace boost;

unsigned long giant[100];

class TestHandler : virtual public TestIf {
 public:
  TestHandler() {
      for (int i = 0; i < 100; i++) {
          giant[i] = -1;
      }
  }


  std::vector<int64_t> & ping() {
        return (std::vector<int64_t> &)giant;
    }

  void ping(std::vector<int64_t> & bla) {}
};

int main(int argc, char **argv) {

  shared_ptr<TestHandler> handler(new TestHandler());
  shared_ptr<TProcessor> processor(new TestProcessor(handler));
  shared_ptr<TServerTransport> serverTransport(new TServerSocket(port));
  shared_ptr<TTransportFactory> transportFactory(new TBufferedTransportFactory());
  shared_ptr<TProtocolFactory> protocolFactory(new TBinaryProtocolFactory());

  TSimpleServer server(processor,
                       serverTransport,
                       transportFactory,
                       protocolFactory);

  printf("Starting the server...\n");
  server.serve();
  printf("done.\n");
  return 0;
}

Answer 1

I accidentally came across an article (StackOverflow: Handling Apache Thrift List Map Return Types in C) that discussed this exact issue (though the answer didn't work in my case). Turns out, thrift uses a pass-by-reference syntax, even though "Thrift uses a pass by value model" - Gupta. So here's an example:

.thrift file

service Test {

    list<string> ping();
}

Server side

void ping(std::vector<string> & _return) {
    _return.push_back("hello");    //initialize the vector _return with values "hello","world"
    _return.push_back("world");
}

Client side

std::vector<string> result;     //create vector "result" for storing the values
client.ping(result);
printf("%s %s!\n", result[0].c_str(), result[1].c_str());   //c_str() turns the vector string into a C-style string

Client output (after starting server)

hello world!

and thank you Thrift for the lack of documentation, I had a blast! #4hoursgoogling&crying