base85

Base85 encoder/decoder written in native javascript.

Where base64 adds approximately 1/3, base85 only adds about 1/4. Of course there's a tradeoff. The Base85 alphabet includes characters that might not be as friendly as the base64 alphabet. While it's still only printable characters, the Ascii85 specification contains quotes (' and ") which needs escaping in many programming languages, and the ZeroMQ specification contains < and > which need escaping in most (all?) SGML languages.

IPv6 encoding is implemented, even though RFC 1924 was published on April 1st. It should only be used for encoding IPv6 addresses. When using IPv6, input for encoding must always be 16 bytes, and input for decoding must always be 20 bytes.

ZeroMQ's version (z85) requires according to the specification) string input to be divisible by 5, and binary input to be divisible by 4. This module includes a z85pad version which uses the same alphabet but does not enforce, or indeed require, this restriction.

The ascii85 encoding frames the base85 string between <~ and ~>. Use the alternate a85 version if you don't want that.

Supported encoding specifications

• Ascii85
• btoa
• ZeroMQ
• IPv6

Installation

npm install base85

Usage

Encoding:

var base85 = require('base85');

var z85 = base85.encode('Hello, world!!!!');
console.log(z85); // nm=QNz.92Pz/PV8aT50L

Decoding:

var base85 = require('base85');

var decoded = base85.decode('vqG:5Cw?IqayPd#az#9uAbn%daz>L5wPF#evpK6}vix96y?$k6z*rGH');
console.log(decoded.toString('utf8')); // all work and no play makes jack a dull boy!!

IPv6 (RFC1924), can take any correctly formatted IPv6 address:

var base85 = require('base85');

var ipv6 = base85.encode('2001:db8:100:f101::1', 'ipv6');
console.log(ipv6); // 9R}vSQZ1W=8fRv3*HAqn

var decoded = base85.decode('9R}vSQZ1W=8fRv3*HAqn', 'ipv6');
console.log(decoded); // 2001:db8:100:f101::1

API

encode(data [, encoding])

Encodes the specified data. If encoding is ascii85, the encoded data will be prepended with <~ and appended with ~>.

data

The data to encode, may be a String or a Buffer.

encoding

Which specification to use when encoding data. Valid values are: ascii85, z85 or ipv6. Default is z85.

For ipv6, if data is a buffer, it is expected to be the binary representation of an IPv6 address (16 bytes). It cannot be a textual representation. If it is a string, it can be on any valid IPv6 form (e.g. ::1 or 1080:0:0:0:8:800:200c:417a, parsing is done using ip-address).

returns

A String with the encoded data.

decode(data [, encoding])

Decodes the specified data. If encoding is ascii85, the data is expected to start with <~ and and end with ~>. No checks are actually made for this, but output will be unexpected if this is not the case. If encoding is ipv6, the length of data must be exactly 20 bytes. ipv6 encoding cannot be used with arbitrary data.

A buffer is always returned as data may not be representable in a string. If you know it is, you can easily convert it to a string using the Buffer.toString() utility.

data

The data to decode. May be a String or a Buffer. If ascii85, it is expected to be enclosed in <~ and ~>.

encoding

Which specification data is encoded with. Valid values are: ascii85, z85 or ipv6. Default is z85.

returns

A Buffer With the decoded data, or boolean false if the buffer could not be decoded. When testing if the result succeeded, always use operators with 3 characters ('===' or '!==').

Which specification to use?

ZeroMQ appears to be a better specification for most applications. It doesn't include quotes in its alphabet which makes it useful in many quoted languages (such as C, C++, JavaScript, Java, Python, Perl, Ruby... the list goes on). Neither does it add the 4 extra enclosing bytes Ascii85 does. There may, however, be some problems using it in SGML and its derivatives since both less-than < and greater-than > are part of the alphabet. But then again, Ascii85 has that as well.

Ascii85 appears to be the most used of the base85 specifications however. As for why completely eludes me. This may very well be the only reason to pick Ascii85.

If you control both decoding and encoding side, use ZeroMQ, or the z85pad version if your buffers may not be a multiple of 4 bytes long.

If you need interoperability with Ascii85, use that.

As IPv6 encoding only supports exactly 128 bits (16 bytes), this is not very useful for arbitrary data. Only use IPv6 if you're actually encoding IPv6 addresses. (Also note the issuance date of RFC 1924.)

History

This module was originally written by Alexander Olsson [email protected], published here. This fork adds streamlined setup code, more alphabets, and options for non-4-byte-aligned ZMP encoding.

I plan to fold this back into Alexander's code, if possible.

Bugs

This module is intended to be a functional superset of all other base85 codecs on NPM. If anything is missing, please file a bug.

IPv6 encoding specification (RFC1924) requires 128-bit arithmetic, which is rather problematic. I'm thrilled to see that the author of the RFC took this in consideration, specifically - quote from the RFC: "This is not considered a serious drawback in the representation, but a flaw of the processor designs." Silly processor designers. Currently, this is implemented using an arbitrary precision algorithm, it's slow but it does the job. Now let's poke those processor designers for 128-bit processors.