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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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If we have a file on disk and the hashes are the same in the new Release
file and the old one we have on disk we know that if we ask the server
for the file, we will at best get an IMS hit – at worse the server
doesn't support this and sends us the (unchanged) file and we have to
run all our checks on it again for nothing. So, we can save ourselves
(and the servers) some unneeded requests if we figure this out on our
own.
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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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Not all servers we are talking to support If-Modified-Since and some are
not even sending Last-Modified for us, so in an effort to detect such
hits we run a hashsum check on the 'old' compared to the 'new' file, we
got the hashes for the 'new' already for "free" from the methods anyway
and hence just need to calculated the old ones.
This allows us to detect hits even with unsupported servers, which in
turn means we benefit from all the new hit behavior also here.
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Especially pdiff-enhanced downloads have the tendency to fail for
various reasons from which we can recover and even a successful download
used to leave the old unpatched index in partial/.
By adding a new method responsible for making the transaction of an
individual file happen we can at specialisations especially for abort
cases to deal with the cleanup.
This also helps in keeping the compressed indexes around if another
index failed instead of keeping the decompressed files, which we
wouldn't pick up in the next call.
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If we get a IMSHit for the Transaction-Manager (= the InRelease file or
as its still supported fallback Release + Release.gpg combo) we can
assume that every file we would queue based on this manager, but already
have locally is current and hence would get an IMSHit, too. We therefore
save us and the server the trouble and skip the queuing in this case.
Beside speeding up repetative executions of 'apt-get update' this way we
also avoid hitting hashsum errors if the indexes are in fact already
updated, but the Release file isn't yet as it is the case on well
behaving mirrors as Release files is updated last.
The implementation is a bit harder than the theory makes it sound as we
still have to keep reverifying the Release files (e.g. to detect now expired
once to avoid an attacker being able to silently stale us) and have to
handle cases in which the Release file hits, but some indexes aren't
present (e.g. user added a new foreign architecture).
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The worker expects that the methods tell him when they start or finish
downloading a file. Various information pieces are passed along in this
report including the (expected) filesize. https was using a "global"
struct for reporting which made it 'reuse' incorrect values in some
cases like a non-existent InRelease fallbacking to Release{,.gpg}
resulting in a size-mismatch warning. Reducing the scope and redesigning
the setting of the values we can fix this and related issues.
Closes: 777565, 781509
Thanks: Robert Edmonds and Anders Kaseorg for initial patchs
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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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Adds a new testwarning which tests for zero exit and the presents of a
warning in the output, failing if either is not the case or if an error
is found, too. This allows us to change testsuccess to accept only
totally successful executions (= without warnings) which should help
finding regressions.
Git-Dch: Ignore
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These functions check the exit code of the command, but for apt commands
we can go further and require an error message for non-zero exits and
none for zero exits.
Git-Dch: Ignore
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Git-Dch: Ignore
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I am pretty sure I did that before committing broken stuff…
Git-Dch: Ignore
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Communicate the fail reason from the methods to the parent
and Rename() failed files.
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This option controls the maximum size of Release/Release.gpg/InRelease
files. The rational is that we do not know the size of these files in
advance and we want to protect against a denial of service attack
where someone sends us endless amounts of data until the disk is full
(we do know the size all other files (Packages/Sources/debs)).
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