id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
27545	Django conditional If-Match: * returns precondition failed response	David Harrigan	nobody	"I believe there is a small bug in how `If-Match: *` behavior is supposed to work in Django version <= 1.10.  I know that 1.11 is migrating to RFC-7232 specification conditional header, and that version <= 1.10 implements according to RFC-2616.

Expected behavior of `If-Match: *` according to RFC-2616:
> If any of the entity tags match the entity tag of the entity that
> would have been returned in the response to a similar GET request
> (without the If-Match header) on that resource, or if ""*"" is given
> and any current entity exists for that resource, then the server MAY
> perform the requested method as if the If-Match header field did not
> exist.

So if `*` is given as the field-value, Django should allow the process to continue as long as the entity exits.

Current behavior:  https://github.com/django/django/blob/1.10.3/django/utils/cache.py#L184

Where `etag` variable is the etag for the entity in question.

{{{
# returns precondition failed if this evaluates to true
(not etag and '*' in etags) or (etag and etag not in etags) 
}}}

**Problem**: * in etags not considered here if `etag` is present.  According to the RFC,  as long as the entity is present on the server,  If-Match: * should yield in as If-Match header was not given by the client.   This scenario here in Django implementation results in precondition failed.  

I believe the above code should be re-written as something like:
{{{
not etag or                                          # not etag == no entity, so always return a 412
not ('*' in etags or etag in etags)    # allow * in etags or client specified etag in etags
}}}
"	Bug	closed	HTTP handling	1.10	Normal	wontfix	precondition, etags, etag,  if-match		Unreviewed	0	0	0	0	0	0