Re: CHANGE PROPOSAL: Remove ping and hyperlink auditing (ISSUE-1 and ISSUE-2)

On Sun, 06 Dec 2009 01:47:22 -0000, Roy T. Fielding <>  

> Regarding ISSUE-1 (PINGPOST) and ISSUE-2 (PINGUI), this is a
> formal change proposal to remove the ping attribute and all
> mention of hyperlink auditing from the HTML5 specification.
> The feature is half-baked, insufficiently implemented, and
> therefore not yet suitable for standardization.

It was thoroughly discussed, had experimental implementation and has been  
redesigned in response to feedback. That's about the same as most HTML 5  

> Hyperlink auditing is important because advertising and
> referral-based user tracking are two of the primary means of
> generating revenue via Web sites.  However, by its very nature,
> such tracking must be comprehensive, accurate, and unavoidable
> by a typical user or it simply won't be relied upon by site
> owners and advertisers.  The ping feature is incapable of
> providing such accuracy.

That's a good point. It would be nice to get feedback from advertisers  
about this.

However ad tracking isn't the only use-case for ping. Search engines don't  
need perfectly reliable tracking of clicks on results, but need tracking  
to be unobtrusive. Similarly e-commerce sites may want to track which page  
elements are used most. has nice feature of marking links as  
visited on server-side, so they're synchronized between computers, and  
ping could be used for that too.

E-mail newsletters usually track all links. It would be great if they  
could track clicks without obscuring URLs (letting anti-spam filters see  
all links).

> The ping feature was added to HTML based on speculation that
> an optional mechanism would be usable instead of the typical
> redirect, javascript, or gateway-based tracking mechanisms.
> However, it cannot be used reliably until all browsers have
> implemented ping, are deployed, and do not configure it "off"
> by default.  Sites would therefore either ignore the ping
> feature until all of the browsers turn it on or use it only
> for secondary counts, thus duplicating the traffic that already
> handles this functionality.

Yes, there will be lengthy adoption period, but should we just give up now  
because of this?

Trackers similar to Google Analytics' TrackEvent API could use ping where  
available (set it via DOM instead of creating an image). It's also  
possible to do other way round, and emulate ping with JavaScript (AJAX,  
cookies or local storage + images) where there's no native implementation.

The important part is that browsers may make ping requests most efficient  
and least disruptive for users as possible (e.g. multiple requests  
buffered and then pipelined, and might even be sent with lowest QoS).

Perhaps ping should be exposed as JavaScript API as well? It might be  
easier for current trackers to use and JavaScript page counters could use  
it as well.

> Ping would never be capable of proving undercounts [the sole
> apparent reason for this new feature] because there is no
> guarantee that the two DNS requests will deliver equally
> reachable servers for the ping and href, nor that the href
> request will succeed before the ping succeeds, nor that the
> href URL corresponds to the ping-per-referral URL.  It is for
> all of those reasons that people use redirects, referer,
> javascript, and cookies today to do tracking and those will
> never be solved by ping.

With redirects you don't have guarantee that final destination will be  
reachable either. It's not uncommon for redirects to go through several  
parties, and each of them could break the chain.

Ping gets users to landing page quicker and with higher probability.

> Also, as described in ISSUE-1, ping's use of POST causes an
> unsafe method to be used in response to a safe activation request,
> in violation of the method constraints that have been part of
> Web architecture since 1992.

Is current widespread practice of using GET specifically for triggering  
side-effects better? If so, then ping can be made to use that too.

> In short, if the UI is being presented as a normal link, then the
> HTTP methods resulting from the user's selection must all be safe
> (GET/HEAD/OPTIONS/etc.).  While some user agents may already fail
> to protect the user in that regard, that is not an excuse to add
> another broken feature to the standard.

I think it is. There's no point worrying about weak link in a chain that  
is already broken in few places (form.submit() or submit button with  
CSS/type=image are far more dangerous). Today servers/applications without  
CSRF protection cannot be considered safe.

Switching to "safe" method may make very little difference in practice.  
Web applications that don't need body of POST at all are very likely to be  
exploitable via GET requests as well (e.g. PHP using register_globals  

The spec could say that non-graphical UAs that don't support JavaScript  
are not allowed to support ping either, and AFAIK there will be no new  

ping is easier to block than other CSRF exploits. Given that it's a new  
feature with very specific purpose, servers could even be shipped with  
ping requests blocked by default.

> That would also solve ISSUE-2 (PINGUI), which the past two years have
> demonstrated that implementing a preferences UI should at least
> be figured out before it is demanded of all implementations.

Disabling of ping can be coupled with disabling of Referer header and 3rd  
party cookies. They are similar and figured out.

Ping may be disabled when browsing in "private" mode (definition of this  
mode varies between browsers, so not all may choose to do it) or by  
browser extensions like TORButton and NoScript (both block it already!)

I don't think ping needs more than that. It's certainly unreasonable to  
expect that users will manually check every tracking URL before clicking  
on any link. Auditing of tracking URLs has to be done automatically, and  
ping allows that.

There are already nastier tracking methods in widespread use that lack UI.  
To compete with them ping probably even _shouldn't_ have UI. Anyway, it  
gives browsers full control and tracking URLs, so browsers have a lot of  
freedom with UI implementation, if any is ever needed.

regards, Kornel LesiƄski

Received on Monday, 7 December 2009 23:33:44 UTC