blob-utils-module.js
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blob-utils-module.js
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	// @flow

	import { requireNativeModule } from 'expo-modules-core';
	import RNBlob from 'react-native/Libraries/Blob/Blob.js';
	import BlobManager from 'react-native/Libraries/Blob/BlobManager.js';
	import type { BlobData } from 'react-native/Libraries/Blob/BlobTypes.js';

	const BlobUtilsModule: {
	+copyBlobToTypedArray: (blob: BlobData, destination: Uint8Array) => void,
	+blobFromTypedArray: (data: $TypedArray) => string,
	} = requireNativeModule('BlobUtils');

	function arrayBufferFromBlob(blob: Blob): ArrayBuffer {
	// $FlowFixMe: react-native Blob type is incompatible with global Blob type
	const rnBlob = (blob: RNBlob);
	if (!(rnBlob instanceof RNBlob)) {
	throw new Error(
	'Given blob is not a React Native blob. Missing "data" property.',
	);
	}
	const blobData = rnBlob.data;

	const resultArray = new Uint8Array(blob.size);
	BlobUtilsModule.copyBlobToTypedArray(blobData, resultArray);
	return resultArray.buffer;
	}

	function blobFromArrayBuffer(arrayBuffer: ArrayBuffer, type?: string): Blob {
	const typedArray = new Uint8Array(arrayBuffer);
	const blobID = BlobUtilsModule.blobFromTypedArray(typedArray);
	const reactNativeBlob = BlobManager.createFromOptions({
	blobId: blobID,
	offset: 0,
	size: arrayBuffer.byteLength,
	type: type \|\| '',
	lastModified: Date.now(),
	});

	// $FlowFixMe: react-native Blob type is incompatible with global Blob type
	// $FlowFixMe: even though they have the same properties
	return (reactNativeBlob: Blob);
	}

	export { arrayBufferFromBlob, blobFromArrayBuffer };