The CFTPClient missing ability to upload data stored in memory. My proposal is the following: extend the CFTPClient with public methods:

1. bool UploadFile(read_callback_t read_callback, void* userData, const std::string &strRemoteFile, const bool &bCreateDir = false) const;
2. bool UploadFile(std::istream &isData, const std::string &strRemoteFile, const bool &bCreateDir = false) const;

First one correspond to CURLOPT_READFUNCTION and second one is useful wrapper for std::istream. Implementation of
bool UploadFile(const std::string &strLocalFile, const std::string &strRemoteFile, const bool &bCreateDir = false) const; could be updated therefore to open strLocalFile with std::ifstream and call overload 2).