37 lines
1.4 KiB
JavaScript
37 lines
1.4 KiB
JavaScript
import { alphabetByEncoding, bitsPerByte, bitsPerLetter } from "./constants.browser";
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export const fromBase64 = (input) => {
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let totalByteLength = (input.length / 4) * 3;
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if (input.slice(-2) === "==") {
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totalByteLength -= 2;
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}
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else if (input.slice(-1) === "=") {
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totalByteLength--;
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}
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const out = new ArrayBuffer(totalByteLength);
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const dataView = new DataView(out);
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for (let i = 0; i < input.length; i += 4) {
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let bits = 0;
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let bitLength = 0;
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for (let j = i, limit = i + 3; j <= limit; j++) {
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if (input[j] !== "=") {
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if (!(input[j] in alphabetByEncoding)) {
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throw new TypeError(`Invalid character ${input[j]} in base64 string.`);
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}
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bits |= alphabetByEncoding[input[j]] << ((limit - j) * bitsPerLetter);
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bitLength += bitsPerLetter;
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}
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else {
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bits >>= bitsPerLetter;
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}
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}
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const chunkOffset = (i / 4) * 3;
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bits >>= bitLength % bitsPerByte;
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const byteLength = Math.floor(bitLength / bitsPerByte);
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for (let k = 0; k < byteLength; k++) {
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const offset = (byteLength - k - 1) * bitsPerByte;
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dataView.setUint8(chunkOffset + k, (bits & (255 << offset)) >> offset);
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}
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}
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return new Uint8Array(out);
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};
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