The normalized form of the X-Timestamp header looks like a float with a fixed
width to ensure stable string sorting - normalized timestamps look like
"1402464677.04188"
To support overwrites of existing data without modifying the original
timestamp but still maintain consistency a second internal offset
vector is append to the normalized timestamp form which compares and
sorts greater than the fixed width float format but less than a newer
timestamp. The internalized format of timestamps looks like
"1402464677.04188_0000000000000000" - the portion after the underscore
is the offset and is a formatted hexadecimal integer.
The internalized form is not exposed to clients in responses from Swift.
Normal client operations will not create a timestamp with an offset.
The Timestamp class in common.utils supports internalized and normalized
formatting of timestamps and also comparison of timestamp values. When the
offset value of a Timestamp is 0 - it's considered insignificant and need not
be represented in the string format; to support backwards compatibility during
a Swift upgrade the internalized and normalized form of a Timestamp with an
insignificant offset are identical. When a timestamp includes an offset it
will always be represented in the internalized form, but is still excluded
from the normalized form. Timestamps with an equivalent timestamp portion
(the float part) will compare and order by their offset. Timestamps with a
greater timestamp portion will always compare and order greater than a
Timestamp with a lesser timestamp regardless of it's offset. String
comparison and ordering is guaranteed for the internalized string format, and
is backwards compatible for normalized timestamps which do not include an
offset.
The reconciler currently uses a offset bump to ensure that objects can move to
the wrong storage policy and be moved back. This use-case is valid because
the content represented by the user-facing timestamp is not modified in way.
Future consumers of the offset vector of timestamps should be mindful of HTTP
semantics of If-Modified and take care to avoid deviation in the response from
the object server without an accompanying change to the user facing timestamp.
DocImpact
Implements: blueprint storage-policies
Change-Id: Id85c960b126ec919a481dc62469bf172b7fb8549
Rework header handling and add some methods needed by the reconciler.
* response headers are case insensitive HeaderKeyDicts
* add direct client container obj put and delete
* add headers param to direct head object
* add headers to DirectClientException
DirectClientException is a subclass of ClientException with a convience
constructor. ClientException now supports an http_headers kwarg.
Exceptions raised from direct_client will include headers.
DocImpact
Implements: blueprint storage-policies
Change-Id: Ia484d569619df0bf85f973e4e916de2ac6401d5e
Unit tests in test/unit only have one dependency
to swiftclient in test_direct_client.py. This one
can be easily avoided and this patch removes it.
Change-Id: Ic1c78bc7f7fe426e8f7d8209a783342a0c4f071f
Enhance internally logged messages to report referer and user-agent.
Pass the referering URL and METHOD between internal servers (when
known), and set the user-agent to be the server type (obj-server,
container-server, proxy-server, obj-updater, obj-replicator,
container-updater, direct-client, etc.) with the process PID. In
conjunction with the transaction ID, it helps to track down which PID
from a given system was responsible for initiating the request and
what that server was working on to make this request.
This has been helpful in tracking down interactions between object,
container and account servers.
We also take things a bit further performaing a bit of refactoring to
consolidate calls to transfer_headers() now that we have a helper
method for constructing them.
Finally we performed further changes to avoid header key duplication
due to string literal header key values and the various objects
representing headers for requests and responses. See below for more
details.
====
Header Keys
There seems to be a bit of a problem with the case of the various
string literals used for header keys and the interchangable way
standard Python dictionaries, HeaderKeyDict() and HeaderEnvironProxy()
objects are used.
If one is not careful, a header object of some sort (one that does not
normalize its keys, and that is not necessarily a dictionary) can be
constructed containing header keys which differ only by the case of
their string literals. E.g.:
{ 'x-trans-id': '1234', 'X-Trans-Id': '5678' }
Such an object, when passed to http_connect() will result in an
on-the-wire header where the key values are merged together, comma
separated, that looks something like:
HTTP_X_TRANS_ID: 1234,5678
For some headers in some contexts, this is behavior is desirable. For
example, one can also use a list of tuples which enumerate the multiple
values a single header should have.
However, in almost all of the contexts used in the code base, this is
not desirable.
This behavior arises from a combination of factors:
1. Header strings are not constants and different lower-case and
title-case header strings values are used interchangably in the
code at times
It might be worth the effort to make a pass through the code to
stop using string literals and use constants instead, but there
are plusses and minuses to doing that, so this was not attempted
in this effort
2. HeaderEnvironProxy() objects report their keys in ".title()"
case, but normalize all other key references to the form
expected by the Request class's environ field
swob.Request.headers fields are HeaderEnvironProxy() objects.
3. HeaderKeyDict() objects report their keys in ".lower()" case,
and normalize all other key references to ".lower()" case
swob.Response.headers fields are HeaderKeyDict() objects.
Depending on which object is used and how it is used, one can end up
with such a mismatch.
This commit takes the following steps as a (PROPOSED) solution:
1. Change HeaderKeyDict() to normalize using ".title()" case to
match HeaderEnvironProxy()
2. Replace standard python dictionary objects with HeaderKeyDict()
objects where possible
This gives us an object that normalizes key references to avoid
fixing the code to normalize the string literals.
3. Fix up a few places to use title case string literals to match
the new defaults
Change-Id: Ied56a1df83ffac793ee85e796424d7d20f18f469
Signed-off-by: Peter Portante <peter.portante@redhat.com>
