Implement FileReader.readAsArrayBuffer

[Smarticles101]

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]

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

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[mgscreativa]

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!

[AdrianoRuberto]

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;
}

[seigel]

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