67 lines
1.7 KiB
JavaScript
67 lines
1.7 KiB
JavaScript
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"use strict";
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/**
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* btoa() as defined by the HTML and Infra specs, which mostly just references
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* RFC 4648.
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*/
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function btoa(s) {
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let i;
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// String conversion as required by Web IDL.
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s = `${s}`;
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// "The btoa() method must throw an "InvalidCharacterError" DOMException if
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// data contains any character whose code point is greater than U+00FF."
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for (i = 0; i < s.length; i++) {
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if (s.charCodeAt(i) > 255) {
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return null;
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}
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}
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let out = "";
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for (i = 0; i < s.length; i += 3) {
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const groupsOfSix = [undefined, undefined, undefined, undefined];
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groupsOfSix[0] = s.charCodeAt(i) >> 2;
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groupsOfSix[1] = (s.charCodeAt(i) & 0x03) << 4;
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if (s.length > i + 1) {
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groupsOfSix[1] |= s.charCodeAt(i + 1) >> 4;
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groupsOfSix[2] = (s.charCodeAt(i + 1) & 0x0f) << 2;
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}
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if (s.length > i + 2) {
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groupsOfSix[2] |= s.charCodeAt(i + 2) >> 6;
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groupsOfSix[3] = s.charCodeAt(i + 2) & 0x3f;
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}
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for (let j = 0; j < groupsOfSix.length; j++) {
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if (typeof groupsOfSix[j] === "undefined") {
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out += "=";
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} else {
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out += btoaLookup(groupsOfSix[j]);
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}
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}
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}
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return out;
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}
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/**
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* Lookup table for btoa(), which converts a six-bit number into the
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* corresponding ASCII character.
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*/
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function btoaLookup(idx) {
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if (idx < 26) {
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return String.fromCharCode(idx + "A".charCodeAt(0));
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}
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if (idx < 52) {
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return String.fromCharCode(idx - 26 + "a".charCodeAt(0));
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}
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if (idx < 62) {
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return String.fromCharCode(idx - 52 + "0".charCodeAt(0));
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}
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if (idx === 62) {
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return "+";
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}
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if (idx === 63) {
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return "/";
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}
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// Throw INVALID_CHARACTER_ERR exception here -- won't be hit in the tests.
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return undefined;
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}
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module.exports = btoa;
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