"use strict";
/**
* Implementation of atob() according to the HTML and Infra specs, except that
* instead of throwing INVALID_CHARACTER_ERR we return null.
*/
function atob(data) {
if (arguments.length === 0) {
throw new TypeError("1 argument required, but only 0 present.");
}
// Web IDL requires DOMStrings to just be converted using ECMAScript
// ToString, which in our case amounts to using a template literal.
data = `${data}`;
// "Remove all ASCII whitespace from data."
data = data.replace(/[ \t\n\f\r]/g, "");
// "If data's length divides by 4 leaving no remainder, then: if data ends
// with one or two U+003D (=) code points, then remove them from data."
if (data.length % 4 === 0) {
data = data.replace(/==?$/, "");
}
// "If data's length divides by 4 leaving a remainder of 1, then return
// failure."
//
// "If data contains a code point that is not one of
//
// U+002B (+)
// U+002F (/)
// ASCII alphanumeric
//
// then return failure."
if (data.length % 4 === 1 || /[^+/0-9A-Za-z]/.test(data)) {
return null;
}
// "Let output be an empty byte sequence."
let output = "";
// "Let buffer be an empty buffer that can have bits appended to it."
//
// We append bits via left-shift and or. accumulatedBits is used to track
// when we've gotten to 24 bits.
let buffer = 0;
let accumulatedBits = 0;
// "Let position be a position variable for data, initially pointing at the
// start of data."
//
// "While position does not point past the end of data:"
for (let i = 0; i < data.length; i++) {
// "Find the code point pointed to by position in the second column of
// Table 1: The Base 64 Alphabet of RFC 4648. Let n be the number given in
// the first cell of the same row.
//
// "Append to buffer the six bits corresponding to n, most significant bit
// first."
//
// atobLookup() implements the table from RFC 4648.
buffer <<= 6;
buffer |= atobLookup(data[i]);
accumulatedBits += 6;
// "If buffer has accumulated 24 bits, interpret them as three 8-bit
// big-endian numbers. Append three bytes with values equal to those
// numbers to output, in the same order, and then empty buffer."
if (accumulatedBits === 24) {
output += String.fromCharCode((buffer & 0xff0000) >> 16);
output += String.fromCharCode((buffer & 0xff00) >> 8);
output += String.fromCharCode(buffer & 0xff);
buffer = accumulatedBits = 0;
}
// "Advance position by 1."
}
// "If buffer is not empty, it contains either 12 or 18 bits. If it contains
// 12 bits, then discard the last four and interpret the remaining eight as
// an 8-bit big-endian number. If it contains 18 bits, then discard the last
// two and interpret the remaining 16 as two 8-bit big-endian numbers. Append
// the one or two bytes with values equal to those one or two numbers to
// output, in the same order."
if (accumulatedBits === 12) {
buffer >>= 4;
output += String.fromCharCode(buffer);
} else if (accumulatedBits === 18) {
buffer >>= 2;
output += String.fromCharCode((buffer & 0xff00) >> 8);
output += String.fromCharCode(buffer & 0xff);
}
// "Return output."
return output;
}
/**
* A lookup table for atob(), which converts an ASCII character to the
* corresponding six-bit number.
*/
const keystr =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
function atobLookup(chr) {
const index = keystr.indexOf(chr);
// Throw exception if character is not in the lookup string; should not be hit in tests
return index < 0 ? undefined : index;
}
module.exports = atob;