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Re: Zero-edits Counter Proposal for Issues 1 and 2 (Ping)

From: Julian Reschke <julian.reschke@gmx.de>
Date: Wed, 17 Feb 2010 16:41:11 +0100
Message-ID: <4B7C0E17.3070302@gmx.de>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
CC: public-html@w3.org
On 17.02.2010 16:30, Tab Atkins Jr. wrote:
> On Wed, Feb 17, 2010 at 8:18 AM, Julian Reschke<julian.reschke@gmx.de>  wrote:
>> On 15.02.2010 16:48, Tab Atkins Jr. wrote:
>>>
>>> ...
>>>>
>>>> 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.
>>>
>>> POST is the correct method to use to reflect @ping's semantics.
>>> ...
>>
>> It's not! It is!
>>
>> Not helpful.
>>
>> Citing Roy again:
>>
>> "The actions generated by a user agent should be consistent
>> with the actions selected by the user.  That is why TimBL had an axiom
>> about GET being safe -- clicking on a link (or a spider wandering
>> around) must be translated into a safe network action because to do
>> otherwise would require every user to know the purpose of every
>> resource before the GET.  It follows, therefore, that the UI for a
>> user action that is safe (a link) must be rendered differently from
>> all other actions that might be unsafe.
>>
>> 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. Implementors are responsible
>> for their own implementations.  We are only responsible for the
>> standards by which those implementations are judged broken."
>>
>> So, *if* you want to "ping" a server, better use a method defined to be
>> safe. BTW: this doesn't rule out defining a new method.
>
> A ping url causes a change on the server.  That's it's entire purpose;
> it *must* be unsafe to follow multiple times.  So you can't ever try
> and call a ping url "safe", because *by definition* it isn't.
> ...

<http://greenbytes.de/tech/webdav/rfc2616.html#rfc.section.9.1.1>:

"9.1.1 Safe Methods

Implementors should be aware that the software represents the user in 
their interactions over the Internet, and should be careful to allow the 
user to be aware of any actions they might take which may have an 
unexpected significance to themselves or others.

In particular, the convention has been established that the GET and HEAD 
methods SHOULD NOT have the significance of taking an action other than 
retrieval. These methods ought to be considered "safe". This allows user 
agents to represent other methods, such as POST, PUT and DELETE, in a 
special way, so that the user is made aware of the fact that a possibly 
unsafe action is being requested.

Naturally, it is not possible to ensure that the server does not 
generate side-effects as a result of performing a GET request; in fact, 
some dynamic resources consider that a feature. The important 
distinction here is that the user did not request the side-effects, so 
therefore cannot be held accountable for them."

Note the last paragraph - what's relevant is whether the *user* is 
requesting side-effects; and this is *clearly* not the case when 
navigating to another document.

>..
> It's possible that we could define a new method for @ping, call it
> PING.  It would still be "unsafe", that is, not idempotent, by
> definition.  I'm not sure what possible benefits this could bring over
> just using POST, though.
> ...

"safe" and "idempotent" are different things.

Best regards, Julian
Received on Wednesday, 17 February 2010 15:41:52 UTC

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