How can I create a file object through byte array

Question

I got this array from file[0] -> blob.slice -> filereader.asArrayBuffer -> Uint8Array

array = [37, 80, 68, 70, 45, 49, 46, 51, 13, 10, 37, 226, 227, 207, 211, 13, 10, 13, 10, 49, 32, 48, 32, 111, ...]

How could I do the reverse engineer? Create a new File Object from the above array?

I'm creating a file object through

bytes = [37, 80, 68, 70, 45, 49, 46, 51, 13, 10, 37, 226, 227, 207, 211, 13, 10, 13, 10, 49, 32, 48, 32, 111, 98, 106, 13, 10, 60, 60, 13, 10, 47, 84, 121, 112, 101, 32, 47, 67, 97, 116, 97, 108, 111, 103, 13, 10, 47, 79, 117, 116, 108, 105, 110, 101, 115, 32, 50, 32, 48, 32, 82, 13, 10, 47, 80, 97, 103, 101, 115, 32, 51, 32, 48, 32, 82, 13, 10, 62, 62, 13, 10, 101, 110, 100, 111, 98, 106, 13, 10, 13, 10, 50, 32, 48, 32, 111, 98, 106]

let testFile = new File([bytes],"application/pdf")

let testFile = new File(bytes,"application/pdf")

Is my code making sense? If not, how do I convert those bytes into a correct one?

Uncaught TypeError: Cannot read property 'toString' of undefined

content = Uint8Array.from([37, ... 106])

file = new File([content])

reader.readAsArrayBuffer(file);

reader.onload = function (e) {
    const fileType = doTask(e.target.result);
    
}

function doTask(arrBuffer) {
    const byteArray = [];
    for (let i = 0; i < 4; i++) {
        byteArray.push(arrayBuffer[i]);
    }
    let headerContent = '';

    // Create the headerContent
    for (let i = 0; i < byteArray.length; i++) {
        headerContent += byteArray[i].toString(16);
    }
    // Uncaught TypeError: Cannot read property 'toString' of undefined

}

@JonasWilms Actually thats exactly what new File needs, as long as the inner bytes is a typed array. — Bergi
– Bergi, Commented Oct 18, 2019 at 23:16
@bergi oh, I had an instinct ... seems I was completely wrong .. — Jonas Wilms
– Jonas Wilms, Commented Oct 18, 2019 at 23:17
@newBike you're probably looking for bytes = Uint8Array.from([ … ]); return new File([bytes], …) — Bergi
– Bergi, Commented Oct 18, 2019 at 23:18
I'm afraid you're solution is wrong. Please see my update. I could not do it reverse way which means the conversion is not correct. — newBike
– newBike, Commented Oct 18, 2019 at 23:36

marcus.salinas · Accepted Answer · 2021-12-29 21:09:44Z

2

I believe I resolved this. In my situation, I have a Google App Script project I'm working on and the DriveApp Blob class has a .getBytes() function.

What you need to do is take that Byte[] and convert it to an unsigned 8 bit array and pass that to the File constructor. Be sure to also include the second required argument of filename as well.

One example from App Script

var file = DriveApp.getFileById(fileId);
var bytes = file.getBlob().getBytes();
new File([new Uint8Array(bytes)], 'filename', {type: 'mimeType'})

So for anyone else, simply get your byte array data in a variable called bytes. Type is optional, but useful.

new File([new Uint8Array(bytes)], 'filename', {type: 'mimeType'})

answered Dec 29, 2021 at 21:09

marcus.salinas

1,0636 silver badges9 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

How can I create a file object through byte array

Uncaught TypeError: Cannot read property 'toString' of undefined

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Uncaught TypeError: Cannot read property 'toString' of undefined

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related