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Why Multi-Status is a 2xx Response

From: Yaron Goland <yarong@microsoft.com>
Date: Sun, 14 Feb 1999 14:28:08 -0800
Message-ID: <3FF8121C9B6DD111812100805F31FC0D08792F04@RED-MSG-59>
To: "'Joe Orton'" <jeo101@york.ac.uk>, jamsden@us.ibm.com
Cc: w3c-dist-auth@w3.org
Before we dive into this we need to get some terms defined. There are two
different kinds of responses discussed below. Response line codes and body
response codes. For example:

   HTTP/1.1 207 Multi-Status
   Content-Type: text/xml; charset="utf-8"
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:"
   xmlns:Z="http://www.w3.com/standards/z39.50">
     <D:response>
          <D:href>http://www.foo.com/bar.html</D:href>
          <D:propstat>
               <D:prop><Z:Authors/></D:prop>
               <D:status>HTTP/1.1 424 Failed Dependency</D:status>
          </D:propstat>
     </D:response>
   </D:multistatus>

In the previous the response line code, the code returned in the HTTP
response line, is 207. The body response code, one of many possible codes
included in the body of a Multi-Status response, is 424. Now, back to the
show.

So I send a PROPFIND request to a resource and get back a 207 Multi-Status
response line code filled with 4xx body response codes telling me that the
properties I was looking for aren't defined, I'm not authorized, etc. So why
did I get back a 2xx response line code? The method clearly failed.

So I sent a PROPPATCH request to a resource and get back a 207 Multi-Status
response line code telling me that one of the changes didn't work so all the
changes were aborted. Why did I get back a 2xx response line code? The
method clearly failed.

So I sent a COPY/MOVE/DELETE with a Depth: Infinity header and got back a
207 Multi-Status response line code telling me that absolutely nothing got
COPYied, MOVEd, or DELETEd. Why did I get back a 2xx response line code? The
method clearly failed!

When Multi-Status was first defined the authors considered having a 2xx
response line code and a 4xx response line code for Multi-Status. So if I
send in a PROPFIND and the resulting Multi-Status comes back with nothing
but 2xx body response codes inside of it then I would use the 2xx response
line code. If I send in a PROPFIND and the resulting Multi-Status comes back
with nothing but 4xx body response codes inside of it then I would use the
4xx response line code. But what happens if the PROPFIND comes back with
nothing but 5xx body response codes? Do I need a 5xx response line code
Multi-Status? What about 3xx body response codes?

However the key case was as follows: I send a PROPFIND request asking for
three properties. One property came back with a 200 O.k. body response code.
One property came back with a 403 Forbidden body response code. The last
property came back with a 500 Server Error body response code. What response
line code should be used?

Initially the authors thought that in a mixed case one should just use a 4xx
response line code. But no one could come up with a compelling reason why a
mixed case should be called a failure instead of a success. In fact, no one
could come up with a case where it mattered if a mixed response was returned
using a 2xx, 4xx or 5xx response line code. In fact, no one could come up
with a reason to have multiple Multi-Status responses. The response line
code just wasn't that useful.

Response line codes in HTTP serve two purposes. The primary purpose is to
provide exact information regarding the result of a request. If that was
their only purpose then there wouldn't be error classes (e.g. 1xx, 2xx, 3xx,
4xx and 5xx response line codes). The reason error classes were introduced
is to allow a client to do something intelligent in case the client doesn't
recognize a response code.

In the case of Multi-Status the error class isn't terribly relevant. Baring
implementation error it isn't possible to get a 207 unless you were
expecting it. PROPFIND and PROPPATCH both require understanding
Multi-Status, as does COPY/MOVE/DELETE if a Depth header is used. Thus we
never have to worry about someone receiving a 207 without being able to
understand it. If you got a 207 it can only be because you made a request
whose definition requires you to understand 207.

While this logic is sound it ignores the bigger picture. Future generations
are quite likely to use 207 and equally like to muck things up and use it in
a context where someone receiving it may not have expected it. However they
will expect to be able to rely on the response class and the response class
fails them here because it will always be 207 even if everything inside of
it is a failure.

In the end however, the mixed error case refused to admit a sensible
solution. So rather than mucking up the protocol with a large number of
response line codes with arcane rules specifying their use we decided to
keep matters simple and return a single response line code.

> -----Original Message-----
> From: Joe Orton [mailto:jeo101@york.ac.uk]
> Sent: Friday, January 22, 1999 11:12 AM
> To: jamsden@us.ibm.com
> Cc: w3c-dist-auth@w3.org
> Subject: Re: Multistatus responses
> 
> 
> 
> > It is my understanding that methods only return a 
> multistatus when they
> > effect multiple resources.
> 
> PROPPATCH uses 207 responses for methods on single resources, I think?
> 
> > So for example, you could DELETE a collection and get a 
> multistatus if
> > it failed indicating which resource in the collection couldn't be
> > deleted. If the DELETE failed because the collection itself 
> was locked,
> > then you could also return a single status as the members were
> > unaffected.
> 
> Yes, so if it failed, why not return a 4xx class response 
> which is what
> 4xx class responses are for? The 'degree' to which it failed 
> (i.e., which
> resources couldn't be deleted) is indicated only by the 
> response body, but
> the bottom line is that the request did NOT succeed, which is what 2xx
> responses are for.
> 
> I'm not trying to suggest that multistatus responses should 
> be scrapped,
> only that they should not have a fixed status code.
> 
> Regads,
> 
> joe
> 
> -- 
> Joe Orton
> jeo101@york.ac.uk ... joe@orton.demon.co.uk
> http://www.orton.demon.co.uk/
> 
> 
> 
Received on Sunday, 14 February 1999 17:28:12 GMT

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