code: public OkRequest<T> part(final String name, final String filename,
                               final String contentType, final InputStream part) throws IOException {
  
          try {
              startPart();
              writePartHeader(name, filename, contentType);
              copy(part, mOutput);
          } catch (IOException ex) {
              throw ex;
          } catch (Exception ex) {
              VolleyLog.e(ex, "error on part");
          }
  
  
          return this;
      }
docs: Write part of a multipart request to the request body
  
  @param name
  @param filename
  @param contentType value of the Content-Type part header
  @param part
  @return this request