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Diffstat (limited to 'school/node_modules/abab/lib/atob.js')
-rw-r--r-- | school/node_modules/abab/lib/atob.js | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/school/node_modules/abab/lib/atob.js b/school/node_modules/abab/lib/atob.js new file mode 100644 index 0000000..c8f753a --- /dev/null +++ b/school/node_modules/abab/lib/atob.js @@ -0,0 +1,101 @@ +"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; |