code: private MultipartContent createContent(final ProblemInput input, final File output, final File source) throws IOException {
  		final HttpMediaType type = new HttpMediaType(MEDIA_TYPE);
  		type.setParameter(BOUNDARY, createBoundary());
  		// Submission from Chrome through contest website sends fake path for security,
  		// which presumes the server only uses the last token to generate the downloadable
  		// zip. It is possible to submit real path here (source.getAbsolutePath) but to
  		// preserve user privacy a fake path will do source.getName() might be sufficient
  		// as well but it's not tested using a fake path is the safest option since that's
  		// what Chrome does.
  		final String sourceFilePath = new StringBuilder(PATH_PREFIX)
  			.append(source.getName())
  			.toString();
  		final MultipartContent content = new MultipartContent()
  			.setMediaType(type)
  			.addPart(HttpRequestExecutor.buildDataPart(CSRF_PARAMETER_NAME, values.getToken()))
  			.addPart(HttpRequestExecutor.buildFilePart(ANSWER_PARAMETER, output))
  			.addPart(HttpRequestExecutor.buildFilePart(SOURCE_FILE_PARAMETER, source))
  			.addPart(HttpRequestExecutor.buildDataPart(SOURCE_FILE_NAME_PARAMETER, sourceFilePath))
  			.addPart(HttpRequestExecutor.buildDataPart(COMMAND_PARAMETER_NAME, SUBMIT_COMMAND))
  			.addPart(HttpRequestExecutor.buildDataPart(PROBLEM_PARAMETER_NAME, input.getProblem().getId()))
  			.addPart(HttpRequestExecutor.buildDataPart(INPUT_ID_PARAMETER_NAME, String.valueOf(input.getNumber())))
  			.addPart(HttpRequestExecutor.buildDataPart(NUM_SOURCE_FILE_PARAMETER, DEFAULT_NUM_SOURCE_FILE))
  			.addPart(HttpRequestExecutor.buildDataPart(AGENT_PARAMETER_NAME, DEFAULT_AGENT));
  		return content;
  	}
docs: <p>Created and returns a valid {@link MultipartContent} instance
  that contains data required for submission.</p>
  
  @param input Input file to submit solution for.
  @param output Output file produced by the algorithm.
  @param source Source code file of the algorithm to submit.
  @return Created multipart content.