C++, JsonCpp, libcurl and UTF-8 woes

Question

I had some problems making libcurl work with C++ JsonCpp library and, after a lot of research, I came up with this code:

int post(const string& call, const string& key, const string& value) {
  // (...)

  char* char_data=NULL; 
  struct curl_slist *headers=NULL;

  headers = curl_slist_append(headers, "Content-Type: application/json; charset=UTF-8");

  Json::Value root;
  root[key] = value;

  Json::StyledWriter writer;
  string data = writer.write(root);

  char_data = (char*) malloc((strlen(data.c_str())+1) * sizeof(char));
  strcpy(char_data, data.c_str());

  curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headers); 
  curl_easy_setopt(curl, CURLOPT_POSTFIELDS, char_data);
  curl_easy_setopt(curl, CURLOPT_POSTFIELDSIZE, (long)strlen(char_data));

  // (...)
}

This works fine, as long as the data (C++ std::string that holds the JSON string representation) doesn't have any non-ascii chars. When it does, I get an error from the backend (written in Rails 3):

Started POST "/deployments/4c904f607d7c4249cf00002c/log.json" for 67.23.79.89 at Wed Sep 15 00:45:40 -0400 2010
  Processing by DeploymentsController#log as JSON
  Parameters: {"log"=>"0 upgraded, 0 newly \214\211K########talled, 0 to remove and 46 not upgraded.\n", "id"=>"4c904f607d7c4249cf00002c"}
Completed   in 6ms

BSON::InvalidStringEncoding (String not valid UTF-8):
  app/models/deployment.rb:161:in `log'
  app/models/deployment.rb:160:in `each'
  app/models/deployment.rb:160:in `log'
  app/controllers/deployments_controller.rb:54:in `log'

What is the best way to take a C++ sctring (in this case data), and safely convert it UTF-8, and then to a *char variable that would play nice with libcurl?

Answer 1

I found the problem. It wasn't on that part of code. I was actually doing a string split that was causing the problem.