Data URI <img src=“https://travis-ci.org/dball/data_uri.png” alt=“Build Status” />¶ ↑

Data URIs allow resources to be embedded inside a URI. The URI::Data class provides support for parsing these URIs using the normal URI.parse method.

I wrote it to support embedding binary data inside JSON messages in a relatively reasonable way. If you find some other use for it, please drop me a line.

require 'data_uri'

uri = URI::Data.new('data:image/gif;base64,...')
uri.content_type # image/gif
uri.data # Base64 decoded data

Data URIs can play nicely with open-uri:

require 'open-uri'
require 'data_uri/open_uri'

open(uri) do |io|
  io.content_type # image/gif
  io.read # decoded data
end

There is no support for creating data URI strings, but it would be trivial to add if anyone’s interested.

URI.parse knows about URI::Data, but unfortunately, its regexp for splitting URIs into components maxes out at 92 characters for an opaque URI, which is far too small to be useful for data URIs.

It accepts URIs with charset MIME parameters:

data:text/html;charset=utf-8,...

and if the String object has a force_encoding method, as in ruby-1.9.x, it will call it with the value of the charset parameter on the decoded data. Other MIME parameters are parsed and stored, but are not exposed.

The base64 pseudo-parameter must appear immediately prior to the data, as per the RFC. Google Chrome apparently misbehaves in this regard, so if this causes grief to anyone, yell and I’ll relax the constraint. If base64 coding is not specified, the data are URI decoded.

Some non-authoritative documentation about data URIs state that whitespace is allowed and ignored within them. The RFC seems to contradict this interpretation, but support seems to be widespread in the browser world. URI::Data cannot parse URIs containing whitespace. If this causes grief to anyone, yell and I’ll either add a class method to URI::Data for explicit relaxed parsing, and/or figure out how to convince URI::Generic to be more open minded about the kinds of URIs it allows.

Even when using the open-uri support file, Kernel.open will not accept string data URIs, only URI::Data objects. Open-uri is opinionated about the formats of the URIs it will try to open, and it’s ambiguous to me at least if data URIs can necessarily be distinguished from filesystem paths on all platforms. Again, if this causes undue pain and suffering, we can commit minor violence to open-uri to convince it to see reason.

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Copyright © 2010 Donald Ball <donald.ball@gmail.com>

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