Jump to content

data URI scheme

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by 49.237.200.71 (talk) at 01:05, 17 April 2024 (http://blog.teamtreehouse.com/using-data-uris-speed-website|title=Using Data URIs to Speed Up Your Website|date=27 March 2014|publisher=Treehouse Blog}}</ref> and used by several browser extensions to package images as well as other multimedia content in a single HTML file for page saving.<ref>{{cite web|url=https://chrome.google.com/webstore/detail/singlefile/mpiodijhokgodhhofbcjdecpffjipkle|title=SingleFile - Chrome Web Store|website=Chrome Web Store|access-date=25 August 2018}}</ref><ref>{...). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

The data URI scheme is a uniform resource identifier (URI) scheme that provides a way to include data in-line in Web pages as if they were external resources. It is a form of file literal or here document. This technique allows normally separate elements such as images and style sheets to be fetched in a single Hypertext Transfer Protocol (HTTP) request, which may be more efficient than multiple HTTP requests,Cite error: A <ref> tag is missing the closing </ref> (see the help page). Note that Base64-encoded data: URIs use the standard Base64 character set (with '+' and '/' as characters 62 and 63) rather than the so-called "URL-safe Base64" character set.

Examples of data URIs showing most of the features are: 

data:text/vnd-example+xyz;foo=bar;base64,R0lGODdh
data:text/plain;charset=UTF-8;page=21,the%20data:1234,5678
(outputs: "the data:1234,5678")
data:image/jpeg;base64,/9j/4AAQSkZJRgABAgAAZABkAAD
data:image/svg+xml;utf8,<svg width='10'... </svg>

The minimal data URI is data:,, consisting of the scheme, no media-type, and zero-length data.

Thus, within the overall URI syntax, a data URI consists of a scheme and a path, with no authority part, query string, or fragment. The optional media type, the optional base64 indicator, and the data are all parts of the URI path.

Examples of use

HTML

An HTML fragment embedding a base64 encoded PNG picture of a small red dot: 

<img alt="" src="data:image/png;base64,iVBORw0KGgoAAA
ANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4
//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU
5ErkJggg==" style="width:36pt;height:36pt" />

In this example, the lines are broken for formatting purposes. In actual URIs, including data URIs, control characters (ASCII 0 to 31, and 127) and spaces (ASCII 32) are "excluded characters". This means that whitespace characters are not permitted in data URIs. However, in the context of HTML 4 and HTML 5, linefeeds within an element attribute value (such as the "src" above) are ignored[citation needed]. So the data URI above would be processed ignoring the linefeeds, giving the correct result. But note that this is an HTML feature, not a data URI feature, and in other contexts, it is not possible to rely on whitespace within the URI being ignored.

An HTML fragment embedding a utf8 encoded SVG picture of a small red dot: 

<img alt="Red dot" src="data:image/svg+xml;utf8,
<svg width='10' height='10' xmlns='http://www.w3.org/2000/svg'>
 <circle style='fill:red' cx='5' cy='5' r='5'/>
</svg>"/>

In this example, the image data is encoded with utf8 and hence the image data can broken into multiple lines for easy reading. Single quote has to be used in the SVG data as double quote is used for encapsulating the image source.

A favicon can also be made with utf8 encoding and SVG data which has to appear in the 'head' section of the HTML: 

<link rel="icon" href='data:image/svg+xml;utf8,
<svg width="10" height="10" xmlns="http://www.w3.org/2000/svg">
 <circle style="fill:red" cx="5" cy="5" r="5"/>
</svg>'/>

CSS

A Cascading Style Sheets (CSS) rule that includes a background image: 

ul.checklist li.complete {
    padding-left: 20px;
    background: white url('data:image/png;base64,iVB\
ORw0KGgoAAAANSUhEUgAAABAAAAAQAQMAAAAlPW0iAAAABlBMVEU\
AAAD///+l2Z/dAAAAM0lEQVR4nGP4/5/h/1+G/58ZDrAz3D/McH8\
yw83NDDeNGe4Ug9C9zwz3gVLMDA/A6P9/AFGGFyjOXZtQAAAAAEl\
FTkSuQmCC') no-repeat scroll left top;
}

In this example, the \ + <linefeed> line terminators are a feature of CSS, indicating continuation on the next line. These would be removed by the CSS stylesheet processor, and the data URI would be reconstituted without whitespace, making it correct, since whitespace is not allowed within the data component of a data: URI.

JavaScript

A JavaScript statement that opens an embedded subwindow, as for a footnote link: 

window.open('data:text/html;charset=utf-8,' +
    encodeURIComponent( // Escape for URL formatting
        '<!DOCTYPE html>'+
        '<html lang="en">'+
        '<head><title>Embedded Window</title></head>'+
        '<body><h1>42</h1></body>'+
        '</html>'
    )
);

SVG

Example of an SVG image with embedded JPEG images

A Scalable Vector Graphic image containing an embedded JPEG image encoded in Base64: 

<svg>
<image width="64" height="24" href="data:image/jpeg;base64,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="/>
</svg>

Malware and phishing

The data URI can be utilized to construct attack pages that attempt to obtain usernames and passwords from unsuspecting web users. It can also be used to get around cross-site scripting (XSS) restrictions, embedding the attack payload fully inside the address bar, and hosted via URL shortening services rather than needing a full website that is controlled by a third party.[1] As a result, some browsers now block webpages from navigating to data URIs.[2]

References

  1. ^ Phishing without a webpage – researcher reveals how a link itself can be malicious, Naked Security by Sophos, 31 AUG 2012 https://nakedsecurity.sophos.com/2012/08/31/phishing-without-a-webpage-researcher-reveals-how-a-link-itself-can-be-malicious/
  2. ^ "Data URLs - HTTP | MDN". MDN Web Docs. Mozilla. Retrieved 11 May 2018.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Data_URI_scheme&oldid=1219317939"