base65536

Base64 is used to encode arbitrary binary data as "plain" text using a small, extremely safe repertoire of 64 (well, 65) characters. Base64 remains highly suited to text systems where the range of characters available is very small -- i.e., anything still constrained to plain ASCII. Base64 encodes 6 bits, or 3/4 of an octet, per character.

However, now that Unicode rules the world, the range of characters which can be considered "safe" in this way is, in many situations, significantly wider. Base65536 applies the same basic principle to a carefully-chosen repertoire of 65,536 (well, 65,792) Unicode code points, encoding 16 bits, or 2 octets, per character.

In theory, this project could have been a one-liner. In practice, naively taking each pair of bytes and smooshing them together to make a single code point is a bad way to do this because you end up with:

• Control characters
• Whitespace
• Unpaired surrogate pairs
• Normalization corruption
• No way to tell whether the final byte in the sequence was there in the original or not

For details of how these code points were chosen, see the base65536gen sibling project. As indicated by the leading "0." on the version number of both projects, these choices of "safe" code points are potentially subject to backwards-incompatible breaking changes which retroactively corrupt all existing Base65536 texts.

Installation

npm install base65536

Usage

var base65536 = require('base65536');
 
var buf = new Buffer("hello world"); // 11 bytes 
 
var str = base65536.encode(buf); 
console.log(str); // 6 code points, "驨ꍬ啯𒁷ꍲᕤ" 
 
var buf2 = base65536.decode(str);
console.log(buf.equals(buf2)); // true 

API

base65536.encode(buf)

Encodes a Buffer and returns a Base65536 String, suitable for passing safely through almost any "Unicode-clean" text-handling API. This string contains no special characters and is immune to Unicode normalization. The string encodes two bytes per code point.

Note

While you might expect that the length of the resulting string is half the length of the original buffer, this is only true when counting Unicode code points. In JavaScript, a string's length property reports not the number of code points but the number of 16-bit code units in the string. For characters outside of the Basic Multilingual Plane, a surrogate pair of 16-bit code units is used to represent each code point. base65536 makes extensive use of these characters.

As a worked example:

var buf = new Buffer([255, 255]);    // two bytes 
var str = base65536.encode(buf);     // "𨗿", one code point, U+285FF 
console.log(str.length);             // 2, two 16-bit code units 
console.log(str.charCodeAt(0));      // 55393 = 0xD861 
console.log(str.charCodeAt(1));      // 56831 = 0xDDFF 
console.log(str === "\uD861\uDDFF"); // true 

base65536.decode(str)

Decodes a Base65536 String and returns a Buffer containing the original binary data.

This function is currently very strict, with no tolerance for whitespace or other unexpected characters. An Error is thrown if the supplied string is not a valid Base65536 text, or if there is a "final byte" code point in the middle of the string.

Why?

Erm.

I wanted people to be able to share HATETRIS replays via Twitter.

Twitter supports tweets of up to 140 characters. "Tweet length is measured by the number of codepoints in the NFC normalized version of the text."

HATETRIS has four buttons: left, right, down and rotate. A single move in HATERIS therefore encodes two bits of information. At present, replays are encoded as hexadecimal and spaced for legibility/selectability. Although a game of HATETRIS may extend for an arbitrary number of keystrokes (simply press rotate forever), in general, the longer the game goes on, the higher one's score.

The world record HATETRIS replay (30 points) is 1,440 keystrokes = 2,880 bits long. At present, HATETRIS replays are encoded as hexadecimal, with each hexadecimal digit encoding 4 bits = 2 keystrokes, and spaces added for clarity/legibility, then presented as text, like so:

C02A AAAA AAAB 00AA AAAA AC08 AAAA AAC2 AAAA AAAA C2AA AAAA AEAA AAAA AA56 AAAA AAAA B55A AAAA AA96 AAAA AAAA D5AA AAAA A9AA AAAA AAB5 AAAA AAAA AAAA AAAA DAAA AAAA 9756 AAAA AA8A AAAA AAAB AAAA AAAB 5AAA AAAB 56AA AAAA AAAA A82A AAAA B00A AAAA A6D6 AB55 6AAA AAA9 4AAA AAA6 AAAA AD56 AAAA B56A AAAA 032A AAAA A65B F00A AAAA AA6E EFC0 2AAA AAAA EB00 AAAA AAA8 0AAA AAAA 802A AAAA AA54 AAAA AAA1 AAAA AAA0 AAAA AAA0 0AAA AAAA C02A AAAA B002 AAAA B00A AAAC 2AAA AAB0 AAAA AEAA AAA9 5AAA AAA9 D5AA AAA5 AAAA AAB5 6AAA A6AA AAAB 5AAA AAAA AAAA DAAA AAD5 56AA AA2A AAAA BAAA AAD6 AAAB 56AA AAAA 82AA AC02 AAA7 B5AA D556 AAAA 52AA A6AA B55A AB56 AA80 FCAA AAA5 583F 0AAA A9BB BF00 AAAA AE80 32AA AA82 FAAA A802 AAAA 96AA AA1A AAA8 2AAA A00A AAAB 00AA AB00 AAB0 AAAB 0AAB AAA9 5AAA AD56 AA5A AAB5 6AAC 02A9 AAAB 5AAA AAAD AAB5 5AA2 AAAE AA0A AAB2 AAD5 6AB5 AA02 AAA0 0AAA B55A AD6A BAAC 2AAB 0AA0 C2AA C02A

That's 899 characters including spaces, or 720 characters if the spaces were removed. Were the hexadecimal characters converted to binary, I would have 360 bytes, and were the binary expressed in Base64, I would have 480 characters.

Using elementary run-length encoding, with two bits of keystroke and two bits of run length, I get down to 2040 bits. That's 255 bytes, which is still 340 characters of Base64. But in Base65536 this is 128 code points! Much better.

𤇃𢊻𤄻嶜𤄋𤇁𡊻𤄛𤆬𠲻𤆻𠆜𢮻𤆻ꊌ𢪻𤆻邌𤆻𤊻𤅋𤲥𣾻𤄋𥆸𣊻𤅛ꊌ𤆻𤆱炼綻 𤋅𤅴薹𣪻𣊻𣽻𤇆𤚢𣺻赈𤇣綹𤻈𤇣𤾺𤇃悺𢦻𤂻𤅠㢹𣾻𤄛𤆓𤦹𤊻𤄰炜傼𤞻𢊻𣲻 𣺻ꉌ邹𡊻𣹫𤅋𤇅𣾻𤇄𓎜𠚻𤊻𢊻𤉛𤅫𤂑𤃃𡉌𤵛𣹛𤁐𢉋𡉻𡡫𤇠𠞗𤇡𡊄𡒌𣼻燉𣼋 𦄘炸邹㢸𠞻𠦻𡊻𣈻𡈻𣈛𡈛ꊺ𠆼𤂅𣻆𣫃𤮺𤊻𡉋㽻𣺬𣈛𡈋𤭻𤂲𣈻𤭻𤊼𢈛儛𡈛ᔺ

This fits comfortably in a Tweet, with an extravagant 12 characters left over for your comment.

And of course, the worse you are HATETRIS, the shorter your replay is, and the more you have for invective.

I haven't actually implemented this as part of HATETRIS yet but I'll get to it eventually.

License

MIT