code: def _retrieve_download_url():
      
      try:
          # Try to obtain the url from the Open Hydrology json config file.
          with urlopen(config['nrfa']['oh_json_url'], timeout=10) as f:
              remote_config = json.loads(f.read().decode('utf-8'))
          # This is just for testing, assuming a relative local file path starting with ./
          if remote_config['nrfa_url'].startswith('.'):
              remote_config['nrfa_url'] = 'file:' + pathname2url(os.path.abspath(remote_config['nrfa_url']))
  
          # Save retrieved config data
          _update_nrfa_metadata(remote_config)
  
          return remote_config['nrfa_url']
      except URLError:
          # If that fails (for whatever reason) use the fallback constant.
          return config['nrfa']['url']
docs: Retrieves download location for FEH data zip file from hosted json configuration file.
  
      :return: URL for FEH data file
      :rtype: str