Question

First off, I’ll say I’m not the most competent C++ programmer, but I’m learning, and enjoying the power of Thrift.

I’ve implemented a Thrift Service with some basic functions that return void, i32, and list. I’m using a Python client controlled by a Django web app to make RPC calls and it works pretty well. The generated code is pretty straight forward, except for list returns:

.thrift description file:

namespace cpp Remote

enum N_PROTO {
        N_TCP,
        N_UDP,
        N_ANY
}

service Rcon {
    i32 ping()
    i32 KillFlows()
    i32 RestartDispatch()
    i32 PrintActiveFlows()
    i32 PrintActiveListeners(1:i32 proto)
    list<string> ListAllFlows()
}

The generated signatures from Rcon.h:

  int32_t ping();
  int32_t KillFlows();
  int32_t RestartDispatch();
  int32_t PrintActiveFlows();
  int32_t PrintActiveListeners(const int32_t proto);
  int64_t ListenerBytesReceived(const int32_t id);
  void ListAllFlows(std::vector<std::string> & _return);

As you see, the ListAllFlows() function generated takes a reference to a vector of strings. I guess I expect it to return a vector of strings as laid out in the .thrift description.

I’m wondering if I am meant to provide the function a vector of strings to modify and then Thrift will handle returning it to my client despite the function returning void.

I can find absolutely no resources or example usages of Thrift list<> types in C++. Any guidance would be appreciated.

Answer 1

Ok, I’ve figured it out. It’s pretty simple really.

void ListAllFlows(std::vector<std::string> & _return)
{
    for(int x = 0; x < 5; x++)
    {
        _return.push_back(std::string("hi"));
    }
}

Then the Python client just calls it as it looks in the .thrift file:

result = client.ListAllFlows()
print result # ['hi', 'hi', 'hi', 'hi', 'hi']