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Re: 100 Continue and Expects

From: Mark Pauley <mpauley@apple.com>
Date: Wed, 31 Mar 2010 15:29:07 -0700
Cc: ietf-http-wg@w3.org
Message-Id: <88AE8F09-2892-4DED-BB32-7FBC837B2CB7@apple.com>
To: Adrien de Croy <adrien@qbik.com>
CFNetwork on Mac OSX will send a zero-length post as the first leg of the 3-way auth for NTLM after it has received the initial 4xx response.

CFNetwork ought to soon allow clients to specify Expects and handle the 100 Continue properly to reduce bandwidth on any requests with a large payload, though I can't say when 'soon' will be.  Unfortunately, the NTLM case really is dictated by Microsoft.  Their own behavior shows that they believe it's okay to send a POST with a zero length for the initial NTLM transaction, and since Microsoft is by far the largest producer of NTLM-using server software, CFNetwork just ape's IE.  What about the zero-length post breaks HTTP?  It seems like a POST that both has length 0 and Expects: 100-continue is silly, and the client ought to be able to handle either a 100-continue followed by standard HTTP response or simply just a standard HTTP response.  Garbage in, garbage out.


On Mar 29, 2010, at 5:42 PM, Adrien de Croy wrote:

> 
> I did a review of what browsers do in some cases like this (e.g POST + auth/NTLM) a while back.
> 
> Their behaviour varies.  For instance IE (even current) if it thinks it will get an auth challenge, will submit initial POSTs with a content-length 0 (this breaks a heap of stuff).
> 
> FF and Chrome will send the whole POST body as many times as required to get through auth.
> 
> Server behaviour varies also.  IIS5 for instance will send a 100 continue on all POST requests regardless of whether they contain Expects.  In fact I've never seen a browser send Expects.
> 
> I wrote a I-D partly about this a while back, but it was somewhat misguided, based on my misunderstanding of the Expects mechanism.
> 
> In the end, I think that's the biggest problem with Expects - people expect (pardon the pun) more from it than it delivers.  The reason the history of this list contains numerous discussions about Expects, is because of common misinterpretation.
> 
> The wording in the RFC implies that Expects and 100 Continue can be used to avoid sending the body of a request.  It omits to mention that if indeed you do want to avoid this (e.g. when you get a 3xx or 4xx), you either need to disconnect and re-try, or complete the message some other way (e.g. use chunking and prematurely complete it with a 0 chunk).
> 
> I would really hate to see anyone adopt the 0 chunk approach - it's just as bad as sending Content-Length: 0 when the browser thinks the proxy or server will send an auth challenge.  Browsers second-guessing proxies / servers is not a good option, and when the browser gets it wrong, things get ugly.  We had to write a hack into WinGate to cope with the IE misbehaviour (WinGate only sends an auth challenge when policy dictates auth is required - the browser cannot possibly predict this, and a 0 length post is valid, but breaks websites).  Sending a 0 length chunk tells the proxy the message is complete.  It could then go through many stages of processing that is really undesirable.  There's no way to signal an abort and maintain a connection.
> 
> In the end, the best option IMO is to send the whole thing each time (as per FF and Chrome - sorry don't know what Opera does).  It can be hideously painful with chained connection-oriented auth over a slow link.
> 
> So actually there's no clean solution to this problem.  I proposed a while back a kind of HEAD command for POST to establish a path with credentials before posting a body.  But in the end, any proper solution to this problem will be a significant protocol change to HTTP (since HTTP is designed for intermediaries to be able to work with unknown methods), which means we'll be living with this problem for a long time yet.
> 
> As for NTLM, it's not going away either.  So much as people don't like it because it's not HTTP compliant auth - it's the reality we are stuck with.
> 
> Cheers
> 
> Adrien
> 
> 
> On 30/03/2010 12:22 p.m., Jamie Lokier wrote:
>> Henrik Nordström wrote:
>>   
>>> sön 2010-03-28 klockan 15:20 +0100 skrev Jamie Lokier:
>>>     
>>>> With certain types (Microsoft) of authentication
>>>>       
>>> You forgot to add "which is not true HTTP authentication schemes". That
>>> family of auth schemes makes many assumptions which is opposite the
>>> intentions of the HTTP specifications so using them as an example when
>>> trying to understand the wording of the specification text is not valid.
>>> 
>>> Still interesting when talking about what should be said as they are a
>>> reality and something HTTP has to deal with today, but not when trying
>>> to understand why RFC2616 is written in a certain manner.
>>>     
>> Agreed, Microsoft's version is not standard HTTP.
>> 
>> Regardless of why, it's important to recognise that clients have the
>> option to send the whole request body if they decide to, despite one
>> possible reading of that section of RFC2616 that they must abort.
>> 
>> -- Jamie
>> 
>>   
> 
Received on Wednesday, 31 March 2010 22:29:41 GMT

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