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In 8d041b4f we made apt figure out based on the last Release file it has
if it should request a file or not given that the hashes changed or not.
So if we have a last Release file and do a request, do not sent a
Last-Modified header as we expect a change so much that a non-change
would indeed be an error. The Last-Modified header is therefore at best
ignored by the server, so sending it is just wasted effort. In the worst
case as time is a fragile thing the server decides against sending us an
update with the idea that we already have the latest content, which we
know for a fact that we haven't. Given that we sent less information to
the server our request is on its own also less identifiable as coming
from a returning or new user.
The disadvantage is that if we end up getting an old index file after
getting a new Release file from another mirror the old mirror will not
be able to tell us 'Hit', but instead sends us the complete file we
discard, but both lets us end up with the same error class in the end,
so the difference isn't big in practice.
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Based on a discussion with Niels Thykier who asked for Contents-all this
implements apt trying for all architecture dependent files to get a file
for the architecture all, which is treated internally now as an official
architecture which is always around (like native). This way arch:all
data can be shared instead of duplicated for each architecture requiring
the user to download the same information again and again.
There is one problem however: In Debian there is already a binary-all/
Packages file, but the binary-any files still include arch:all packages,
so that downloading this file now would be a waste of time, bandwidth
and diskspace. We therefore need a way to decide if it makes sense to
download the all file for Packages in Debian or not. The obvious answer
would be a special flag in the Release file indicating this, which would
need to default to 'no' and every reasonable repository would override
it to 'yes' in a few years time, but the flag would be there "forever".
Looking closer at a Release file we see the field "Architectures", which
doesn't include 'all' at the moment. With the idea outlined above that
'all' is a "proper" architecture now, we interpret this field as being
authoritative in declaring which architectures are supported by this
repository. If it says 'all', apt will try to get all, if not it will be
skipped. This gives us another interesting feature: If I configure a
source to download armel and mips, but it declares it supports only
armel apt will now print a notice saying as much. Previously this was a
very cryptic failure. If on the other hand the repository supports mips,
too, but for some reason doesn't ship mips packages at the moment, this
'missing' file is silently ignored (= that is the same as the repository
including an empty file).
The Architectures field isn't mandatory through, so if it isn't there,
we assume that every architecture is supported by this repository, which
skips the arch:all if not listed in the release file.
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This allows running tests in parallel.
Git-Dch: Ignore
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Having every item having its own code to verify the file(s) it handles
is an errorprune process and easy to break, especially if items move
through various stages (download, uncompress, patching, …). With a giant
rework we centralize (most of) the verification to have a better
enforcement rate and (hopefully) less chance for bugs, but it breaks the
ABI bigtime in exchange – and as we break it anyway, it is broken even
harder.
It shouldn't effect most frontends as they don't deal with the acquire
system at all or implement their own items, but some do and will need to
be patched (might be an opportunity to use apt on-board material).
The theory is simple: Items implement methods to decide if hashes need to
be checked (in this stage) and to return the expected hashes for this
item (in this stage). The verification itself is done in worker message
passing which has the benefit that a hashsum error is now a proper error
for the acquire system rather than a Done() which is later revised to a
Failed().
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We use test{success,failure} now all over the place in the framework, so
its only consequencial to do this in the situations in which we test for
a specific output as well.
Git-Dch: Ignore
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Usually they don't provide a lot in terms of what they test, but they
help in covering many lines from strictly anecdotal commands (stats,
moo) and error messages, so that stuff which really needs to be tested,
but isn't is better visible in coverage reports.
Git-Dch: Ignore
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Git-Dch: Ignore
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incorrect invalidating of unauthenticated data (CVE-2014-0488)
incorect verification of 304 reply (CVE-2014-0487)
incorrect verification of Acquire::Gzip indexes (CVE-2014-0489)
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