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[whatwg] Inconsistent behavior for empty-string URLs

From: Nicholas Zakas <nzakas@yahoo-inc.com>
Date: Mon, 7 Dec 2009 10:51:19 -0800
Message-ID: <4E45EC6AD219FD47AD1BC06E4EE3845D0420CDBC@SNV-EXVS09.ds.corp.yahoo.com>


In a recent investigation into capacity issues, I found that there are
several instances where the browser will make a second to the page based
on resolving empty-string URLs in the several tags. I tested four
instances: <img src="">, <link href="">, <script src="">, and <iframe
src="">. Across major browsers today, the behavior is vastly different:


* Internet Explorer 8

  - Make a request for: <img src=""> 

  - Does not make a request for: <link href="">, <script src="">,
<iframe src="">

* Firefox 3

  - Make a request for: <img src="">, <link href="">, <script src=""> 

  - Does not make a request for: < <iframe src="">.

* Firefox 3.5

  - Make a request for: <link href="">, <script src=""> 

  - Does not make a request for: <img src="">,  <iframe src="">

* Safari 4

  - Make a request for:<img src="">,  <link href="">, <script src=""> 

  - Does not make a request for: <iframe src="">

* Chrome 3 (same as Safari)

  - Make a request for:<img src="">,  <link href="">, <script src=""> 

  - Does not make a request for: <iframe src="">

* Opera 10

  - Make a request for: (none) 

  - Does not make a request for: <img src="">,  <link href="">, <script
src="">, <iframe src="">


Presently, HTML5 does provide guidance on the correct behavior for <img
src=""> in section 4.8.2, indicating that Firefox 3.5's and Opera 10's
behavior in this regard is correct:


"If the base URI of the element is the same as the document's address,
then the src attribute's value must not be the empty string."


This seems like it should also apply to the other elements that download
resources automatically. All browsers seem to be in agreement over the
behavior of <iframe src=""> despite a lack of guidance in any HTML spec,
and I'd assume that they will soon all be in agreement over <img
src="">, per the HTML5 spec. It would be nice to formalize this behavior
so that we can get all browsers to act in consistently in these
confusing cases.


My opinion is that Opera is the only browser currently doing this in a
reasonable manner, in that it makes a lot of sense to me that an
empty-string URL for an element that automatically downloads a resource
should be considered invalid and ignored. My hypothesis is that these
patterns are most frequently indications of errors rather than an
intentional use of this little-known behavior, and as a result, sending
another request is an unexpected and unwelcome result. For high-volume
web sites, a single mistaken inclusion of one of these patterns
immediately doubles page views, which can introduce capacity issues
(which I've needed to investigate at least twice in the past three


I'm interested in what others' opinions on this may be, as this seems
like an important area in which to gain consistency.





Commander Lock: "Damnit Morpheus, not everyone believes what you

Morpheus: "My beliefs do not require them to."


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