How to make a Drive API batch request with UrlFetc

I would like to know how to make a Drive API batch request with UrlFetchApp in Google Apps Script. I've read the google documentation but it still isn't clear to me. I want to convert the code below into a batch request accepting multiple file IDs.

var url = 'https://www.googleapis.com/drive/v2/files/FILEID/permissions';

var data = {
    "role":"owner",
    "type":"user",
    "value": NEWOWNER
  };

var response = UrlFetchApp.fetch(url, {
  headers: {
    Authorization: 'Bearer ' + AUTHORIZATIONTOKEN
  },
  method: 'post',
  contentType: 'application/json',
  payload: JSON.stringify(data),
});
var result = JSON.parse(response.getContentText());

I tried using https://www.googleapis.com/drive/v2/files?id=FILEID1&id=FILEID2/permissionsbut it seemed to be not working. I just saw description of nesting each file request to a batch request, but so far I have not found a syntax example for doing it correctly.

Some insight would be helpful. Thanks!

How about this sample script? When I saw this document, I could find that the API calls you want to do batch request are sent using multipart/mixed. By this, I could create a sample script for Google Apps Script as follows.

Sample script :

function myFunction() {
  var body = [
    {
      method: "POST",
      endpoint: "https://www.googleapis.com/drive/v3/files/### fileId 1 ###/permissions",
      requestBody: {
       "role": "owner",
       "type": "user",
       "emailAddress": NEWOWNER
      }
    },
    {
      method: "POST",
      endpoint: "https://www.googleapis.com/drive/v3/files/### fileId 2 ###/permissions",
      requestBody: {
       "role": "owner",
       "type": "user",
       "emailAddress": NEWOWNER
      }
    }
  ];

  var boundary = "xxxxxxxxxx";
  var contentId = 0;
  var data = "--" + boundary + "\r\n";
  for (var i in body) {
        data += "Content-Type: application/http\r\n";
        data += "Content-ID: " + ++contentId + "\r\n\r\n";
        data += body[i].method + " " + body[i].endpoint + "\r\n";
        data += body[i].requestBody ? "Content-Type: application/json; charset=utf-8\r\n\r\n" : "\r\n";
        data += body[i].requestBody ? JSON.stringify(body[i].requestBody) + "\r\n" : "";
        data += "--" + boundary + "\r\n";
  }
  var payload = Utilities.newBlob(data).getBytes();
  var options = {
    method: "post",
    contentType: "multipart/mixed; boundary=" + boundary,
    payload: payload,
    headers: {'Authorization': 'Bearer ' + ScriptApp.getOAuthToken()},
    muteHttpExceptions: true,
  };
  var res = UrlFetchApp.fetch("https://www.googleapis.com/batch", options).getContentText();
  Logger.log(res);
}

Note :

Please modify this sample script for your environment.
If you want more APIs, please add the elements to the array of "body".
It supposes that you have already enabled Drive API.
Drive API can be used the maximum of 100 calls in one batch request. This is a limitation.
For the batch request, each API call is no guaranteed ordering.

In my environment, I confirmed that this works. But if this didn't work in your environment, please tell me. I would like to modify.