get_account_info used to work like this:
* make an account HEAD request
* ignore the response
* get the account info by digging around in the request environment,
where it had been deposited by elves or something
Not actually elves, but the proxy's GETorHEAD_base method would take
the HEAD response and cache it in the response environment, which was
the same object as the request environment, thus enabling
get_account_info to find it.
This was extraordinarily brittle. If a WSGI middleware were to
shallow-copy the request environment, then any middlewares to its left
could not use get_account_info, as the left middleware's request
environment would no longer be identical to the response environment
down in GETorHEAD_base.
Now, get_account_info works like this:
* make an account HEAD request.
* if the account info is in the request environment, return it. This
is an optimization to avoid a double-set in memcached.
* else, compute the account info from the response headers, store it
in caches, and return it.
This is much easier to think about; get_account_info can get and cache
account info all on its own; the cache check and cache set are right
next to each other.
All the above is true for get_container_info as well.
get_info() is still around, but it's just a shim. It was trying to
unify get_account_info and get_container_info to exploit the
commonalities, but the number of times that "if container:" showed up
in get_info and its helpers really indicated that something was
wrong. I'd rather have two functions with some duplication than one
function with no duplication but a bunch of "if container:" branches.
Other things of note:
* a HEAD request to a deleted account returns 410, but
get_account_info would return 404 since the 410 came from the
account controller *after* GETorHEAD_base ran. Now
get_account_info returns 410 as well.
* cache validity period (recheck_account_existence and
recheck_container_existence) is now communicated to
get_account_info via an X-Backend header. This way,
get_account_info doesn't need a reference to the
swift.proxy.server.Application object.
* both logged swift_source values are now correct for
get_container_info calls; before, on a cold cache,
get_container_info would call get_account_info but not pass along
swift_source, resulting in get_account_info logging "GET_INFO" as
the source. Amusingly, there was a unit test asserting this bogus
behavior.
* callers that modify the return value of get_account_info or of
get_container_info don't modify what's stored in swift.infocache.
* get_account_info on an account that *can* be autocreated but has
not been will return a 200, same as a HEAD request. The old
behavior was a 404 from get_account_info but a 200 from
HEAD. Callers can tell the difference by looking at
info['account_really_exists'] if they need to know the difference
(there is one call site that needs to know, in container
PUT). Note: this is for all accounts when the proxy's
"account_autocreate" setting is on.
Change-Id: I5167714025ec7237f7e6dd4759c2c6eb959b3fca
1c88d2cb81