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42 lines
1.5 KiB
JavaScript
42 lines
1.5 KiB
JavaScript
// About base64: https://en.wikipedia.org/wiki/Base64
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/**
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* Converts an array of bytes to base64 encoding
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* @param {ArrayBuffer} binaryData An ArrayBuffer which represents an array of bytes
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* @returns {string} A string containing the base64 encoding of `binaryData`
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*/
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function bufferToBase64 (binaryData) {
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// The base64 encoding uses the following set of characters to encode any binary data as text
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const base64Table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/'
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// Every 3 bytes translates to 4 base64 characters, if we have less than 3 bytes we must append '=' chars as padding
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const padding = 3 - (binaryData.byteLength % 3)
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// Create an instance of Uint8Array, to read from the binaryData array buffer
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const byteView = new Uint8Array(binaryData)
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let result = ''
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// Loop through all bytes in the buffer, in increments of 3 bytes
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for (let i = 0; i < byteView.byteLength; i += 3) {
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// Get the index for the next 4 base64 chars
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const char1 = (byteView[i] & 252) >> 2
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const char2 = ((byteView[i] & 3) << 4) + ((byteView[i + 1] & 240) >> 4)
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const char3 = ((byteView[i + 1] & 15) << 2) + ((byteView[i + 2] & 192) >> 6)
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const char4 = byteView[i + 2] & 63
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result +=
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base64Table[char1] +
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base64Table[char2] +
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base64Table[char3] +
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base64Table[char4]
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}
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// Add padding '=' chars if needed
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if (padding !== 3) {
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const paddedResult = result.slice(0, result.length - padding) + '='.repeat(padding)
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return paddedResult
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}
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return result
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}
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export { bufferToBase64 }
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