FAT has a lot of characters it does not allow in filenames, like ? and *
It's probably the worst offender, but other filesystems also have
limitiations.
In 2011, I made keyFile escape : to handle FAT, but missed the other
characters. It also turns out that when I did that, I was also living
dangerously; any existing keys that contained a : had their object
location change. Oops.
So, adding new characters to escape to keyFile is out. Well, it would be
possible to make keyFile behave differently on a per-filesystem basis, but
this would be a real nightmare to get right. Consider that a rsync special
remote uses keyFile to determine the filenames to use, and we don't know
the underlying filesystem on the rsync server..
Instead, I have gone for a solution that is backwards compatable and
simple. Its only downside is that already generated URL and WORM keys
might not be able to be stored on FAT or some other filesystem that
dislikes a character used in the key. (In this case, the user can just
migrate the problem keys to a checksumming backend. If this became a big
problem, fsck could be made to detect these and suggest a migration.)
Going forward, new keys that are created will escape all characters that
are likely to cause problems. And if some filesystem comes along that's
even worse than FAT (seems unlikely, but here it is 2013, and people are
still using FAT!), additional characters can be added to the set that are
escaped without difficulty.
(Also, made WORM limit the part of the filename that is embedded in the key,
to deal with filesystem filename length limits. This could have already
been a problem, but is more likely now, since the escaping of the filename
can make it longer.)
This commit was sponsored by Ian Downes
SHA3 is still waiting for final standardization.
Although this is looking less likely given
https://www.cdt.org/blogs/joseph-lorenzo-hall/2409-nist-sha-3
In the meantime, cryptohash implements skein, and it's used by some of the
haskell ecosystem (for yesod sessions, IIRC), so this implementation is
likely to continue working. Also, I've talked with the cryprohash author
and he's a reasonable guy.
It makes sense to have an alternate high security hash, in case some
horrible attack is found against SHA2 tomorrow, or in case SHA3 comes out
and worst fears are realized.
I'd also like to support using skein for HMAC. But no hurry there and
a new version of cryptohash has much nicer HMAC code, so I will probably
wait until I can use that version.
This is a massive win on OSX, which doesn't have a sha256sum normally.
Only use external hash commands when the file is > 1 mb,
since cryptohash is quite close to them in speed.
SHA is still used to calculate HMACs. I don't quite understand
cryptohash's API for those.
Used the following benchmark to arrive at the 1 mb number.
1 mb file:
benchmarking sha256/internal
mean: 13.86696 ms, lb 13.83010 ms, ub 13.93453 ms, ci 0.950
std dev: 249.3235 us, lb 162.0448 us, ub 458.1744 us, ci 0.950
found 5 outliers among 100 samples (5.0%)
4 (4.0%) high mild
1 (1.0%) high severe
variance introduced by outliers: 10.415%
variance is moderately inflated by outliers
benchmarking sha256/external
mean: 14.20670 ms, lb 14.17237 ms, ub 14.27004 ms, ci 0.950
std dev: 230.5448 us, lb 150.7310 us, ub 427.6068 us, ci 0.950
found 3 outliers among 100 samples (3.0%)
2 (2.0%) high mild
1 (1.0%) high severe
2 mb file:
benchmarking sha256/internal
mean: 26.44270 ms, lb 26.23701 ms, ub 26.63414 ms, ci 0.950
std dev: 1.012303 ms, lb 925.8921 us, ub 1.122267 ms, ci 0.950
variance introduced by outliers: 35.540%
variance is moderately inflated by outliers
benchmarking sha256/external
mean: 26.84521 ms, lb 26.77644 ms, ub 26.91433 ms, ci 0.950
std dev: 347.7867 us, lb 210.6283 us, ub 571.3351 us, ci 0.950
found 6 outliers among 100 samples (6.0%)
import Crypto.Hash
import Data.ByteString.Lazy as L
import Criterion.Main
import Common
testfile :: FilePath
testfile = "/run/shm/data" -- on ram disk
main = defaultMain
[ bgroup "sha256"
[ bench "internal" $ whnfIO internal
, bench "external" $ whnfIO external
]
]
sha256 :: L.ByteString -> Digest SHA256
sha256 = hashlazy
internal :: IO String
internal = show . sha256 <$> L.readFile testfile
external :: IO String
external = do
s <- readProcess "sha256sum" [testfile]
return $ fst $ separate (== ' ') s
Started with a problem when running addurl on a really long url,
because the whole url is munged into the filename. Ended up doing
a fairly extensive review for places where filenames could get too large,
although it's hard to say I'm not missed any..
Backend.Url had a 128 character limit, which is fine when the limit is 255,
but not if it's a lot shorter on some systems. So check the pathconf()
limit. Note that this could result in fromUrl creating different keys
for the same url, if run on systems with different limits. I don't see
this is likely to cause any problems. That can already happen when using
addurl --fast, or if the content of an url changes.
Both Command.AddUrl and Backend.Url assumed that urls don't contain a
lot of multi-byte unicode, and would fail to truncate an url that did
properly.
A few places use a filename as the template to make a temp file.
While that's nice in that the temp file name can be easily related back to
the original filename, it could lead to `git annex add` failing to add a
filename that was at or close to the maximum length.
Note that in Command.Add.lockdown, the template is still derived from the
filename, just with enough space left to turn it into a temp file.
This is an important optimisation, because the assistant may lock down
a bunch of files all at once, and using the same template for all of them
would cause openTempFile to iterate through the same set of names,
looking for an unused temp file. I'm not very happy with the relatedTemplate
hack, but it avoids that slowdown.
Backend.WORM does not limit the filename stored in the key.
I have not tried to change that; so git annex add will fail on really long
filenames when using the WORM backend. It seems better to preserve the
invariant that a WORM key always contains the complete filename, since
the filename is the only unique material in the key, other than mtime and
size. Since nobody has complained about add failing (I think I saw it
once?) on WORM, probably it's ok, or nobody but me uses it.
There may be compatability problems if using git annex addurl --fast
or the WORM backend on a system with the 255 limit and then trying to use
that repo in a system with a smaller limit. I have not tried to deal with
those.
This commit was sponsored by Alexander Brem. Thanks!
Run the same code git-annex used to get the sha, including its sanity
checking. Much better than old grep. Should detect FreeBSD systems with
sha commands that output in stange format.
This after fielding a bug where git-annex was built with a sha256 program
whose output checked out, but was then run with one that output lines
like:
SHA256 (file) = <sha here>
Which it then parsed as having a SHA256 of "SHA256"!
Now the output of the command is required to be of the right length,
and contain only the right characters.
* SHA*E backends: Exclude non-alphanumeric characters from extensions.
* migrate: Remove leading \ in SHA* checksums, and non-alphanumerics
from extensions of SHA*E keys.
* Bugfix: Remove leading \ from checksums output by sha*sum commands,
when the filename contains \ or a newline. Closes: #696384
* fsck: Still accept checksums with a leading \ as valid, now that
above bug is fixed.
* migrate: Remove leading \ in checksums
The default backend used when adding files to the annex is changed from
SHA256 to SHA256E, to simplify interoperability with OSX, media players,
and various programs that needlessly look at symlink targets.
To get old behavior, add a .gitattributes containing: * annex.backend=SHA256
Make Utility.Process wrap the parts of System.Process that I use,
and add debug logging to them.
Also wrote some higher-level code that allows running an action
with handles to a processes stdin or stdout (or both), and checking
its exit status, all in a single function call.
As a bonus, the debug logging now indicates whether the process
is being run to read from it, feed it data, chat with it (writing and
reading), or just call it for its side effect.
Test suite now passes with -threaded!
I traced back all the hangs with -threaded to System.Cmd.Utils. It seems
it's just crappy/unsafe/outdated, and should not be used. System.Process
seems to be the cool new thing, so converted all the code to use it
instead.
In the process, --debug stopped printing commands it runs. I may try to
bring that back later.
Note that even SafeSystem was switched to use System.Process. Since that
was a modified version of code from System.Cmd.Utils, it needed to be
converted too. I also got rid of nearly all calls to forkProcess,
and all calls to executeFile, which I'm also doubtful about working
well with -threaded.
Using Crypto's version of the hashes would be another option.
I need to benchmark it. The SHA2 library (which provides SHA1 also,
confusing name) may be the fastest option, but is not currently in Debian.
Kqueue needs to remember which files failed to be added due to being open,
and retry them. This commit gets the data in place for such a retry thread.
Broke KeySource out into its own file, and added Eq and Ord instances
so it can be stored in a Set.
Fscking a remote is now supported. It's done by retrieving
the contents of the specified files from the remote, and checking them,
so can be an expensive operation.
(Several optimisations are possible, to speed it up, of course.. This is
the slow and stupid remote fsck to start with.)
Still, if the remote is a special remote, or a git repository that you
cannot run fsck in locally, it's nice to have the ability to fsck it.
If you have any directory special remotes, now would be a good time to
fsck them, in case you were hit by the data loss bug fixed in the
previous release!
There are several places where it's assumed a key can be written on one
line. One is in the format of the .git/annex/unused files. The difficult
one is that filenames derived from keys are fed into git cat-file --batch,
which has a line based input. (And no -z option.)
So, for now it's best to block such keys being created.
Supporting multiple directory hash types will allow converting to a
different one, without a flag day.
gitAnnexLocation now checks which of the possible locations have a file.
This means more statting of files. Several places currently use
gitAnnexLocation and immediately check if the returned file exists;
those need to be optimised.
Many functions took the repo as their first parameter. Changing it
consistently to be the last parameter allows doing some useful things with
currying, that reduce boilerplate.
In particular, g <- gitRepo is almost never needed now, instead
use inRepo to run an IO action in the repo, and fromRepo to get
a value from the repo.
This also provides more opportunities to use monadic and applicative
combinators.
To get old behavior, add a .gitattributes containing: * annex.backend=WORM
I feel that SHA256 is a better default for most people, as long as their
systems are fast enough that checksumming their files isn't a problem.
git-annex should default to preserving the integrity of data as well as git
does. Checksum backends also work better with editing files via
unlock/lock.
I considered just using SHA1, but since that hash is believed to be somewhat
near to being broken, and git-annex deals with large files which would be a
perfect exploit medium, I decided to go to a SHA-2 hash.
SHA512 is annoyingly long when displayed, and git-annex displays it in a
few places (and notably it is shown in ls -l), so I picked the shorter
hash. Considered SHA224 as it's even shorter, but feel it's a bit weird.
I expect git-annex will use SHA-3 at some point in the future, but
probably not soon!
Note that systems without a sha256sum (or sha256) program will fall back to
defaulting to SHA1.
The tricky part about this is that to generate a key, the file must be
present already. Worked around by adding (back) an URL key type, which
is used for addurl --fast.
