Base85 (Ascii85) encode and decode functionality
npm install base85
Base85 encoder/decoder written in native javascript.
Where base64 [adds approximately 1/3][Base64], base85 only [adds about
1/4][Base85]. 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][Base85] specification contains
quotes (' and ") which needs escaping in many programming languages, and
the [ZeroMQ][Base85ZeroMQ] specification contains < and > which need
escaping in most (all?) [SGML][SGML] languages.
IPv6 encoding 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) require [according to the specification][Base85ZeroMQ])
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][Base85]
* [btoa][Base85]
* [ZeroMQ][Base85ZeroMQ]
* [IPv6][Base85IPv6]
npm install base85
var base85 = require('base85');
var z85 = base85.encode('Hello, world!!!!');
console.log(z85); // nm=QNz.92Pz/PV8aT50L
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!!
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
> 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][NodeBuffer].
>
> 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][IPAddress]).
>
> returns
>> A String with the encoded data.
> 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()][NodeBufferToString] utility.
>
> data
>> The data to decode. May be a String or a [Buffer][NodeBuffer].
>> 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][NodeBuffer] 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][JSCompare] ('===' or '!==').
>
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.)
[IPv6 encoding specification (RFC1924)][Base85IPv6] 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][Base85IPv6]: "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.
[Base64]: http://en.wikipedia.org/wiki/Base64
[Base85]: http://en.wikipedia.org/wiki/Ascii85
[NodeBuffer]: http://nodejs.org/api/buffer.html
[NodeBufferToString]: http://nodejs.org/api/buffer.html#buffer_buf_tostring_encoding_start_end
[Base85ZeroMQ]: http://rfc.zeromq.org/spec:32
[Base85IPv6]: http://tools.ietf.org/html/rfc1924
[JSCompare]: http://stackoverflow.com/questions/359494/does-it-matter-which-equals-operator-vs-i-use-in-javascript-comparisons
[SGML]: https://en.wikipedia.org/wiki/Standard_Generalized_Markup_Language
[IPAddress]: https://www.npmjs.com/package/ip-address