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ArrayBufferToBase64.js

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// About base64: https://en.wikipedia.org/wiki/Base64

/**

* Converts an array of bytes to base64 encoding

* @param {ArrayBuffer} binaryData An ArrayBuffer which represents an array of bytes

* @returns {string} A string containing the base64 encoding of `binaryData`

*/

function bufferToBase64 (binaryData) {

// The base64 encoding uses the following set of characters to encode any binary data as text

const base64Table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'

// Every 3 bytes translates to 4 base64 characters, if we have less than 3 bytes we must append '=' chars as padding

const padding = 3 - (binaryData.byteLength % 3)

// Create an instance of Uint8Array, to read from the binaryData array buffer

const byteView = new Uint8Array(binaryData)

let result = ''

// Loop through all bytes in the buffer, in increments of 3 bytes

for (let i = 0; i < byteView.byteLength; i += 3) {

// Get the index for the next 4 base64 chars

const char1 = (byteView[i] & 252) >> 2

const char2 = ((byteView[i] & 3) << 4) + ((byteView[i + 1] & 240) >> 4)

const char3 = ((byteView[i + 1] & 15) << 2) + ((byteView[i + 2] & 192) >> 6)

const char4 = byteView[i + 2] & 63

result +=

base64Table[char1] +

base64Table[char2] +

base64Table[char3] +

base64Table[char4]

}

// Add padding '=' chars if needed

if (padding !== 3) {

const paddedResult = result.slice(0, result.length - padding) + '='.repeat(padding)

return paddedResult

}

return result

}

export { bufferToBase64 }