Post a file with urlFetchApp to a google web app - google-apps-script

Question

I am trying to post any type of file using Google Apps Script to a web app but I am not familiar with doPost.
My code looks like this:
function call(){
var file = getFile('/2.html'); //gets a file from my Google Drive (no point in posting all the code here for that)
var options = {
'method' : 'post',
'payload' : {file : file}
};
var response = UrlFetchApp.fetch('https://script.google.com/macros/s/AKfycbx0aIU_XjOHPXh0P6y2dTMmvGpI6WAuac_Cq5BOGw7nDLRlodT-/exec',options)
Logger.log(response)
This seems to work, although I have read I need to base64 encode a file for it to work properly. That's something I don't really understand.
On the web app side I made a doPost(e) but no matter what I tried to do with 'e' I can't work out what kind of object it is and how to process it. All I want to do really is to save it to Google Drive.
You may be wondering why I am going to these lengths to post the file to disk via a web app when I could save it directly. The reason is I am trying to do the process asynchronously using UrlFetchApp.fetchAll() so I can speed up the process of writing many files to disk at once.

Answer 1

If variable file is of type File, Get Blob from File and base64 encode it:
var options = {
'method' : 'post',
'payload' : Utilities.base64EncodeWebSafe(file.getBlob().getBytes())
};
On receiver web -app, Decode it back:
const doPost = e => {
const file = DriveApp.createFile(
Utilities.newBlob(
Utilities.base64DecodeWebSafe(
e.postData.contents
)
)
)
}

Answer 2

Thanks to #TheMaster. I made some modifications to the code because it resulted in an error because a file name was needed. you'll need your own apps script web app url to go here [APPS SCRIPT WEB APP URL]:
const doPost = e => {
const file = DriveApp.createFile(
Utilities.newBlob(
Utilities.base64DecodeWebSafe(
e.parameter.file
),e.parameter.contentType,e.parameter.fileName
)
)
}
function sendFile(file){
var fileName = file.getName();
var contentType = file.getBlob().getContentType();
var url = "[APPS SCRIPT WEB APP URL]";
var payload = {
fileName: fileName,
contentType : contentType,
file: Utilities.base64EncodeWebSafe(file.getBlob().getBytes())
};
var options = {
method: "POST",
payload: payload,
muteHttpExceptions : true,
};
var res = UrlFetchApp.fetch(url, options).getContentText();
}