Implement FileReader.readAsArrayBuffer

[Logan Stucki]

Description

FileReader.readAsArrayBuffer is not implemented.

Reproducible Demo

https://github.com/facebook/react-native/blob/master/Libraries/Blob/FileReader.js#L83-L85

I plan on working towards implementing this if approved.

[React Native Bot]

We are automatically closing this issue because it does not appear to follow any of the provided issue templates.

Please make use of the bug report template to let us know about a reproducible bug or regression in the core React Native library.

If you'd like to propose a change or discuss a feature request, there is a repository dedicated to Discussions and Proposals you may use for this purpose.

[MGS Creativa]

Hi! I need readAsArrayBuffer implementation too, is there any workaround to use this with expo? I'm using expo to avoid using a mac in the development process.

Thanks!

[Adriano Ruberto]

Hello,
I manage to make it work by using readAsDataURL:

FileReader.prototype.readAsArrayBuffer = function (blob) {
	if (this.readyState === this.LOADING) throw new Error("InvalidStateError");
	this._setReadyState(this.LOADING);
	this._result = null;
	this._error = null;
	const fr = new FileReader();
	fr.onloadend = () => {
		const content = atob(fr.result.substr("data:application/octet-stream;base64,".length));
		const buffer = new ArrayBuffer(content.length);
		const view = new Uint8Array(buffer);
		view.set(Array.from(content).map(c => c.charCodeAt(0)));
		this._result = buffer;
		this._setReadyState(this.DONE);
	};
	fr.readAsDataURL(blob);
}

// from: https://stackoverflow.com/questions/42829838/react-native-atob-btoa-not-working-without-remote-js-debugging
const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=';
const atob = (input = '') => {
	let str = input.replace(/=+$/, '');
	let output = '';

	if (str.length % 4 == 1) {
		throw new Error("'atob' failed: The string to be decoded is not correctly encoded.");
	}
	for (let bc = 0, bs = 0, buffer, i = 0;
		buffer = str.charAt(i++);

		~buffer && (bs = bc % 4 ? bs * 64 + buffer : buffer,
			bc++ % 4) ? output += String.fromCharCode(255 & bs >> (-2 * bc & 6)) : 0
	) {
		buffer = chars.indexOf(buffer);
	}

	return output;
}

[James Seigel]

Is there a way to re-open this issue or do we have to create a new issue?