    {-# LANGUAGE CPP, GeneralizedNewtypeDeriving, BangPatterns #-}
    -----------------------------------------------------------------------------
    -- |
    -- Module      :  Codec.Archive.Tar.Types
    -- Copyright   :  (c) 2007 Bjorn Bringert,
    --                    2008 Andrea Vezzosi,
    --                    2008-2009 Duncan Coutts
    --                    2011 Max Bolingbroke
    -- License     :  BSD3
    --
    -- Maintainer  :  duncan@community.haskell.org
    -- Portability :  portable
    --
    -- Types to represent the content of @.tar@ archives.
    --
    -----------------------------------------------------------------------------
    module Codec.Archive.Tar.Types (

      Entry(..),
      entryPath,
      EntryContent(..),
      FileSize,
      Permissions,
      Ownership(..),
      EpochTime,
      TypeCode,
      DevMajor,
      DevMinor,
      Format(..),

      simpleEntry,
      fileEntry,
      directoryEntry,

      ordinaryFilePermissions,
      executableFilePermissions,
      directoryPermissions,

      TarPath(..),
      toTarPath,
      fromTarPath,
      fromTarPathToPosixPath,
      fromTarPathToWindowsPath,

      LinkTarget(..),
      toLinkTarget,
      fromLinkTarget,
      fromLinkTargetToPosixPath,
      fromLinkTargetToWindowsPath,

      Entries(..),
      mapEntries,
      mapEntriesNoFail,
      foldEntries,
      foldlEntries,
      unfoldEntries,

    #ifdef TESTS
      limitToV7FormatCompat
    #endif
      ) where

    import Data.Int      (Int64)
    import Data.Monoid   (Monoid(..))
    import Data.Semigroup as Sem
    import qualified Data.ByteString       as BS
    import qualified Data.ByteString.Char8 as BS.Char8
    import qualified Data.ByteString.Lazy  as LBS
    import Control.DeepSeq

    import qualified System.FilePath as FilePath.Native
             ( joinPath, splitDirectories, addTrailingPathSeparator )
    import qualified System.FilePath.Posix as FilePath.Posix
             ( joinPath, splitPath, splitDirectories, hasTrailingPathSeparator
             , addTrailingPathSeparator )
    import qualified System.FilePath.Windows as FilePath.Windows
             ( joinPath, addTrailingPathSeparator )
    import System.Posix.Types
             ( FileMode )

    #ifdef TESTS
    import Test.QuickCheck
    import Control.Applicative ((<$>), (<*>), pure)
    import Data.Word (Word16)
    #endif

    type FileSize  = Int64
    -- | The number of seconds since the UNIX epoch
    type EpochTime = Int64
    type DevMajor  = Int
    type DevMinor  = Int
    type TypeCode  = Char
    type Permissions = FileMode

    -- | Tar archive entry.
    --
    data Entry = Entry {

        -- | The path of the file or directory within the archive. This is in a
        -- tar-specific form. Use 'entryPath' to get a native 'FilePath'.
        entryTarPath :: {-# UNPACK #-} !TarPath,

        -- | The real content of the entry. For 'NormalFile' this includes the
        -- file data. An entry usually contains a 'NormalFile' or a 'Directory'.
        entryContent :: !EntryContent,

        -- | File permissions (Unix style file mode).
        entryPermissions :: {-# UNPACK #-} !Permissions,

        -- | The user and group to which this file belongs.
        entryOwnership :: {-# UNPACK #-} !Ownership,

        -- | The time the file was last modified.
        entryTime :: {-# UNPACK #-} !EpochTime,

        -- | The tar format the archive is using.
        entryFormat :: !Format
      }
      deriving (Eq, Show)

    -- | Native 'FilePath' of the file or directory within the archive.
    --
    entryPath :: Entry -> FilePath
    entryPath = fromTarPath . entryTarPath

    -- | The content of a tar archive entry, which depends on the type of entry.
    --
    -- Portable archives should contain only 'NormalFile' and 'Directory'.
    --
    data EntryContent = NormalFile      LBS.ByteString {-# UNPACK #-} !FileSize
                      | Directory
                      | SymbolicLink    !LinkTarget
                      | HardLink        !LinkTarget
                      | CharacterDevice {-# UNPACK #-} !DevMajor
                                        {-# UNPACK #-} !DevMinor
                      | BlockDevice     {-# UNPACK #-} !DevMajor
                                        {-# UNPACK #-} !DevMinor
                      | NamedPipe
                      | OtherEntryType  {-# UNPACK #-} !TypeCode LBS.ByteString
                                        {-# UNPACK #-} !FileSize
        deriving (Eq, Ord, Show)

    data Ownership = Ownership {
        -- | The owner user name. Should be set to @\"\"@ if unknown.
        ownerName :: String,

        -- | The owner group name. Should be set to @\"\"@ if unknown.
        groupName :: String,

        -- | Numeric owner user id. Should be set to @0@ if unknown.
        ownerId :: {-# UNPACK #-} !Int,

        -- | Numeric owner group id. Should be set to @0@ if unknown.
        groupId :: {-# UNPACK #-} !Int
      }
        deriving (Eq, Ord, Show)

    -- | There have been a number of extensions to the tar file format over the
    -- years. They all share the basic entry fields and put more meta-data in
    -- different extended headers.
    --
    data Format =

         -- | This is the classic Unix V7 tar format. It does not support owner and
         -- group names, just numeric Ids. It also does not support device numbers.
         V7Format

         -- | The \"USTAR\" format is an extension of the classic V7 format. It was
         -- later standardised by POSIX. It has some restrictions but is the most
         -- portable format.
         --
       | UstarFormat

         -- | The GNU tar implementation also extends the classic V7 format, though
         -- in a slightly different way from the USTAR format. In general for new
         -- archives the standard USTAR/POSIX should be used.
         --
       | GnuFormat
      deriving (Eq, Ord, Show)

    instance NFData Entry where
      rnf (Entry _ c _ _ _ _) = rnf c

    instance NFData EntryContent where
      rnf x = case x of
          NormalFile       c _  -> rnflbs c
          OtherEntryType _ c _  -> rnflbs c
          _                     -> seq x ()
        where
    #if MIN_VERSION_bytestring(0,10,0)
          rnflbs = rnf
    #else
          rnflbs = foldr (\ !_bs r -> r) () . LBS.toChunks
    #endif

    instance NFData Ownership where
      rnf (Ownership o g _ _) = rnf o `seq` rnf g

    -- | @rw-r--r--@ for normal files
    ordinaryFilePermissions :: Permissions
    ordinaryFilePermissions   = 0o0644

    -- | @rwxr-xr-x@ for executable files
    executableFilePermissions :: Permissions
    executableFilePermissions = 0o0755

    -- | @rwxr-xr-x@ for directories
    directoryPermissions :: Permissions
    directoryPermissions  = 0o0755

    -- | An 'Entry' with all default values except for the file name and type. It
    -- uses the portable USTAR/POSIX format (see 'UstarHeader').
    --
    -- You can use this as a basis and override specific fields, eg:
    --
    -- > (emptyEntry name HardLink) { linkTarget = target }
    --
    simpleEntry :: TarPath -> EntryContent -> Entry
    simpleEntry tarpath content = Entry {
        entryTarPath     = tarpath,
        entryContent     = content,
        entryPermissions = case content of
                             Directory -> directoryPermissions
                             _         -> ordinaryFilePermissions,
        entryOwnership   = Ownership "" "" 0 0,
        entryTime        = 0,
        entryFormat      = UstarFormat
      }

    -- | A tar 'Entry' for a file.
    --
    -- Entry  fields such as file permissions and ownership have default values.
    --
    -- You can use this as a basis and override specific fields. For example if you
    -- need an executable file you could use:
    --
    -- > (fileEntry name content) { fileMode = executableFileMode }
    --
    fileEntry :: TarPath -> LBS.ByteString -> Entry
    fileEntry name fileContent =
      simpleEntry name (NormalFile fileContent (LBS.length fileContent))

    -- | A tar 'Entry' for a directory.
    --
    -- Entry fields such as file permissions and ownership have default values.
    --
    directoryEntry :: TarPath -> Entry
    directoryEntry name = simpleEntry name Directory

    --
    -- * Tar paths
    --

    -- | The classic tar format allowed just 100 characters for the file name. The
    -- USTAR format extended this with an extra 155 characters, however it uses a
    -- complex method of splitting the name between the two sections.
    --
    -- Instead of just putting any overflow into the extended area, it uses the
    -- extended area as a prefix. The aggravating insane bit however is that the
    -- prefix (if any) must only contain a directory prefix. That is the split
    -- between the two areas must be on a directory separator boundary. So there is
    -- no simple calculation to work out if a file name is too long. Instead we
    -- have to try to find a valid split that makes the name fit in the two areas.
    --
    -- The rationale presumably was to make it a bit more compatible with old tar
    -- programs that only understand the classic format. A classic tar would be
    -- able to extract the file name and possibly some dir prefix, but not the
    -- full dir prefix. So the files would end up in the wrong place, but that's
    -- probably better than ending up with the wrong names too.
    --
    -- So it's understandable but rather annoying.
    --
    -- * Tar paths use Posix format (ie @\'/\'@ directory separators), irrespective
    --   of the local path conventions.
    --
    -- * The directory separator between the prefix and name is /not/ stored.
    --
    data TarPath = TarPath {-# UNPACK #-} !BS.ByteString -- path name, 100 characters max.
                           {-# UNPACK #-} !BS.ByteString -- path prefix, 155 characters max.
      deriving (Eq, Ord)

    instance NFData TarPath where
      rnf (TarPath _ _) = () -- fully strict by construction

    instance Show TarPath where
      show = show . fromTarPath

    -- | Convert a 'TarPath' to a native 'FilePath'.
    --
    -- The native 'FilePath' will use the native directory separator but it is not
    -- otherwise checked for validity or sanity. In particular:
    --
    -- * The tar path may be invalid as a native path, eg the file name @\"nul\"@
    --   is not valid on Windows.
    --
    -- * The tar path may be an absolute path or may contain @\"..\"@ components.
    --   For security reasons this should not usually be allowed, but it is your
    --   responsibility to check for these conditions (eg using 'checkSecurity').
    --
    fromTarPath :: TarPath -> FilePath
    fromTarPath (TarPath namebs prefixbs) = adjustDirectory $
      FilePath.Native.joinPath $ FilePath.Posix.splitDirectories prefix
                              ++ FilePath.Posix.splitDirectories name
      where
        name   = BS.Char8.unpack namebs
        prefix = BS.Char8.unpack prefixbs
        adjustDirectory | FilePath.Posix.hasTrailingPathSeparator name
                        = FilePath.Native.addTrailingPathSeparator
                        | otherwise = id

    -- | Convert a 'TarPath' to a Unix\/Posix 'FilePath'.
    --
    -- The difference compared to 'fromTarPath' is that it always returns a Unix
    -- style path irrespective of the current operating system.
    --
    -- This is useful to check how a 'TarPath' would be interpreted on a specific
    -- operating system, eg to perform portability checks.
    --
    fromTarPathToPosixPath :: TarPath -> FilePath
    fromTarPathToPosixPath (TarPath namebs prefixbs) = adjustDirectory $
      FilePath.Posix.joinPath $ FilePath.Posix.splitDirectories prefix
                             ++ FilePath.Posix.splitDirectories name
      where
        name   = BS.Char8.unpack namebs
        prefix = BS.Char8.unpack prefixbs
        adjustDirectory | FilePath.Posix.hasTrailingPathSeparator name
                        = FilePath.Posix.addTrailingPathSeparator
                        | otherwise = id

    -- | Convert a 'TarPath' to a Windows 'FilePath'.
    --
    -- The only difference compared to 'fromTarPath' is that it always returns a
    -- Windows style path irrespective of the current operating system.
    --
    -- This is useful to check how a 'TarPath' would be interpreted on a specific
    -- operating system, eg to perform portability checks.
    --
    fromTarPathToWindowsPath :: TarPath -> FilePath
    fromTarPathToWindowsPath (TarPath namebs prefixbs) = adjustDirectory $
      FilePath.Windows.joinPath $ FilePath.Posix.splitDirectories prefix
                               ++ FilePath.Posix.splitDirectories name
      where
        name   = BS.Char8.unpack namebs
        prefix = BS.Char8.unpack prefixbs
        adjustDirectory | FilePath.Posix.hasTrailingPathSeparator name
                        = FilePath.Windows.addTrailingPathSeparator
                        | otherwise = id

    -- | Convert a native 'FilePath' to a 'TarPath'.
    --
    -- The conversion may fail if the 'FilePath' is too long. See 'TarPath' for a
    -- description of the problem with splitting long 'FilePath's.
    --
    toTarPath :: Bool -- ^ Is the path for a directory? This is needed because for
                      -- directories a 'TarPath' must always use a trailing @\/@.
              -> FilePath -> Either String TarPath
    toTarPath isDir = splitLongPath
                    . addTrailingSep
                    . FilePath.Posix.joinPath
                    . FilePath.Native.splitDirectories
      where
        addTrailingSep | isDir     = FilePath.Posix.addTrailingPathSeparator
                       | otherwise = id

    -- | Take a sanitised path, split on directory separators and try to pack it
    -- into the 155 + 100 tar file name format.
    --
    -- The strategy is this: take the name-directory components in reverse order
    -- and try to fit as many components into the 100 long name area as possible.
    -- If all the remaining components fit in the 155 name area then we win.
    --
    splitLongPath :: FilePath -> Either String TarPath
    splitLongPath path =
      case packName nameMax (reverse (FilePath.Posix.splitPath path)) of
        Left err                 -> Left err
        Right (name, [])         -> Right $! TarPath (BS.Char8.pack name)
                                                      BS.empty
        Right (name, first:rest) -> case packName prefixMax remainder of
          Left err               -> Left err
          Right (_     , (_:_))  -> Left "File name too long (cannot split)"
          Right (prefix, [])     -> Right $! TarPath (BS.Char8.pack name)
                                                     (BS.Char8.pack prefix)
          where
            -- drop the '/' between the name and prefix:
            remainder = init first : rest

      where
        nameMax, prefixMax :: Int
        nameMax   = 100
        prefixMax = 155

        packName _      []     = Left "File name empty"
        packName maxLen (c:cs)
          | n > maxLen         = Left "File name too long"
          | otherwise          = Right (packName' maxLen n [c] cs)
          where n = length c

        packName' maxLen n ok (c:cs)
          | n' <= maxLen             = packName' maxLen n' (c:ok) cs
                                         where n' = n + length c
        packName' _      _ ok    cs  = (FilePath.Posix.joinPath ok, cs)

    -- | The tar format allows just 100 ASCII characters for the 'SymbolicLink' and
    -- 'HardLink' entry types.
    --
    newtype LinkTarget = LinkTarget BS.ByteString
      deriving (Eq, Ord, Show)

    instance NFData LinkTarget where
    #if MIN_VERSION_bytestring(0,10,0)
        rnf (LinkTarget bs) = rnf bs
    #else
        rnf (LinkTarget !_bs) = ()
    #endif

    -- | Convert a native 'FilePath' to a tar 'LinkTarget'. This may fail if the
    -- string is longer than 100 characters or if it contains non-portable
    -- characters.
    --
    toLinkTarget   :: FilePath -> Maybe LinkTarget
    toLinkTarget path | length path <= 100 = Just $! LinkTarget (BS.Char8.pack path)
                      | otherwise          = Nothing

    -- | Convert a tar 'LinkTarget' to a native 'FilePath'.
    --
    fromLinkTarget :: LinkTarget -> FilePath
    fromLinkTarget (LinkTarget pathbs) = adjustDirectory $
      FilePath.Native.joinPath $ FilePath.Posix.splitDirectories path
      where
        path = BS.Char8.unpack pathbs
        adjustDirectory | FilePath.Posix.hasTrailingPathSeparator path
                        = FilePath.Native.addTrailingPathSeparator
                        | otherwise = id

    -- | Convert a tar 'LinkTarget' to a Unix/Posix 'FilePath'.
    --
    fromLinkTargetToPosixPath :: LinkTarget -> FilePath
    fromLinkTargetToPosixPath (LinkTarget pathbs) = adjustDirectory $
      FilePath.Posix.joinPath $ FilePath.Posix.splitDirectories path
      where
        path = BS.Char8.unpack pathbs
        adjustDirectory | FilePath.Posix.hasTrailingPathSeparator path
                        = FilePath.Native.addTrailingPathSeparator
                        | otherwise = id

    -- | Convert a tar 'LinkTarget' to a Windows 'FilePath'.
    --
    fromLinkTargetToWindowsPath :: LinkTarget -> FilePath
    fromLinkTargetToWindowsPath (LinkTarget pathbs) = adjustDirectory $
      FilePath.Windows.joinPath $ FilePath.Posix.splitDirectories path
      where
        path = BS.Char8.unpack pathbs
        adjustDirectory | FilePath.Posix.hasTrailingPathSeparator path
                        = FilePath.Windows.addTrailingPathSeparator
                        | otherwise = id

    --
    -- * Entries type
    --

    -- | A tar archive is a sequence of entries.
    --
    -- The point of this type as opposed to just using a list is that it makes the
    -- failure case explicit. We need this because the sequence of entries we get
    -- from reading a tarball can include errors.
    --
    -- It is a concrete data type so you can manipulate it directly but it is often
    -- clearer to use the provided functions for mapping, folding and unfolding.
    --
    -- Converting from a list can be done with just @foldr Next Done@. Converting
    -- back into a list can be done with 'foldEntries' however in that case you
    -- must be prepared to handle the 'Fail' case inherent in the 'Entries' type.
    --
    -- The 'Monoid' instance lets you concatenate archives or append entries to an
    -- archive.
    --
    data Entries e = Next Entry (Entries e)
                   | Done
                   | Fail e
      deriving (Eq, Show)

    infixr 5 `Next`

    -- | This is like the standard 'unfoldr' function on lists, but for 'Entries'.
    -- It includes failure as an extra possibility that the stepper function may
    -- return.
    --
    -- It can be used to generate 'Entries' from some other type. For example it is
    -- used internally to lazily unfold entries from a 'LBS.ByteString'.
    --
    unfoldEntries :: (a -> Either e (Maybe (Entry, a))) -> a -> Entries e
    unfoldEntries f = unfold
      where
        unfold x = case f x of
          Left err             -> Fail err
          Right Nothing        -> Done
          Right (Just (e, x')) -> Next e (unfold x')

    -- | This is like the standard 'foldr' function on lists, but for 'Entries'.
    -- Compared to 'foldr' it takes an extra function to account for the
    -- possibility of failure.
    --
    -- This is used to consume a sequence of entries. For example it could be used
    -- to scan a tarball for problems or to collect an index of the contents.
    --
    foldEntries :: (Entry -> a -> a) -> a -> (e -> a) -> Entries e -> a
    foldEntries next done fail' = fold
      where
        fold (Next e es) = next e (fold es)
        fold Done        = done
        fold (Fail err)  = fail' err

    -- | A 'foldl'-like function on Entries. It either returns the final
    -- accumulator result, or the failure along with the intermediate accumulator
    -- value.
    --
    foldlEntries :: (a -> Entry -> a) -> a -> Entries e -> Either (e, a) a
    foldlEntries f z = go z
      where
        go !acc (Next e es) = go (f acc e) es
        go !acc  Done       = Right acc
        go !acc (Fail err)  = Left (err, acc)

    -- | This is like the standard 'map' function on lists, but for 'Entries'. It
    -- includes failure as a extra possible outcome of the mapping function.
    --
    -- If your mapping function cannot fail it may be more convenient to use
    -- 'mapEntriesNoFail'
    mapEntries :: (Entry -> Either e' Entry) -> Entries e -> Entries (Either e e')
    mapEntries f =
      foldEntries (\entry rest -> either (Fail . Right) (flip Next rest) (f entry)) Done (Fail . Left)

    -- | Like 'mapEntries' but the mapping function itself cannot fail.
    --
    mapEntriesNoFail :: (Entry -> Entry) -> Entries e -> Entries e
    mapEntriesNoFail f =
      foldEntries (\entry -> Next (f entry)) Done Fail

    -- | @since 0.5.1.0
    instance Sem.Semigroup (Entries e) where
      a <> b = foldEntries Next b Fail a

    instance Monoid (Entries e) where
      mempty  = Done
      mappend = (Sem.<>)

    instance Functor Entries where
      fmap f = foldEntries Next Done (Fail . f)

    instance NFData e => NFData (Entries e) where
      rnf (Next e es) = rnf e `seq` rnf es
      rnf  Done       = ()
      rnf (Fail e)    = rnf e

    -------------------------
    -- QuickCheck instances
    --

    #ifdef TESTS

    instance Arbitrary Entry where
      arbitrary = Entry <$> arbitrary <*> arbitrary <*> arbitraryPermissions
                        <*> arbitrary <*> arbitraryEpochTime <*> arbitrary
        where
          arbitraryPermissions :: Gen Permissions
          arbitraryPermissions = fromIntegral <$> (arbitrary :: Gen Word16)

          arbitraryEpochTime :: Gen EpochTime
          arbitraryEpochTime = arbitraryOctal 11

      shrink (Entry path content perms author time format) =
          [ Entry path' content' perms author' time' format
          | (path', content', author', time') <-
             shrink (path, content, author, time) ]
       ++ [ Entry path content perms' author time format
          | perms' <- shrinkIntegral perms ]

    instance Arbitrary TarPath where
      arbitrary = either error id
                . toTarPath False
                . FilePath.Posix.joinPath
              <$> listOf1ToN (255 `div` 5)
                             (elements (map (replicate 4) "abcd"))

      shrink = map (either error id . toTarPath False)
             . map FilePath.Posix.joinPath
             . filter (not . null)
             . shrinkList shrinkNothing
             . FilePath.Posix.splitPath
             . fromTarPathToPosixPath

    instance Arbitrary LinkTarget where
      arbitrary = maybe (error "link target too large") id
                . toLinkTarget
                . FilePath.Native.joinPath
              <$> listOf1ToN (100 `div` 5)
                             (elements (map (replicate 4) "abcd"))

      shrink = map (maybe (error "link target too large") id . toLinkTarget)
             . map FilePath.Posix.joinPath
             . filter (not . null)
             . shrinkList shrinkNothing
             . FilePath.Posix.splitPath
             . fromLinkTargetToPosixPath

    listOf1ToN :: Int -> Gen a -> Gen [a]
    listOf1ToN n g = sized $ \sz -> do
        n <- choose (1, min n (max 1 sz))
        vectorOf n g

    listOf0ToN :: Int -> Gen a -> Gen [a]
    listOf0ToN n g = sized $ \sz -> do
        n <- choose (0, min n sz)
        vectorOf n g

    instance Arbitrary EntryContent where
      arbitrary =
        frequency
          [ (16, do bs <- arbitrary;
                    return (NormalFile bs (LBS.length bs)))
          , (2, pure Directory)
          , (1, SymbolicLink    <$> arbitrary)
          , (1, HardLink        <$> arbitrary)
          , (1, CharacterDevice <$> arbitraryOctal 7 <*> arbitraryOctal 7)
          , (1, BlockDevice     <$> arbitraryOctal 7 <*> arbitraryOctal 7)
          , (1, pure NamedPipe)
          , (1, do c  <- elements (['A'..'Z']++['a'..'z'])
                   bs <- arbitrary;
                   return (OtherEntryType c bs (LBS.length bs)))
          ]

      shrink (NormalFile bs _)   = [ NormalFile bs' (LBS.length bs')
                                   | bs' <- shrink bs ]
      shrink  Directory          = []
      shrink (SymbolicLink link) = [ SymbolicLink link' | link' <- shrink link ]
      shrink (HardLink     link) = [ HardLink     link' | link' <- shrink link ]
      shrink (CharacterDevice ma mi) = [ CharacterDevice ma' mi'
                                       | (ma', mi') <- shrink (ma, mi) ]
      shrink (BlockDevice     ma mi) = [ BlockDevice ma' mi'
                                       | (ma', mi') <- shrink (ma, mi) ]
      shrink  NamedPipe              = []
      shrink (OtherEntryType c bs _) = [ OtherEntryType c bs' (LBS.length bs')
                                       | bs' <- shrink bs ]

    instance Arbitrary LBS.ByteString where
      arbitrary = fmap LBS.pack arbitrary
      shrink    = map LBS.pack . shrink . LBS.unpack

    instance Arbitrary BS.ByteString where
      arbitrary = fmap BS.pack arbitrary
      shrink    = map BS.pack . shrink . BS.unpack

    instance Arbitrary Ownership where
      arbitrary = Ownership <$> name <*> name
                            <*> idno <*> idno
        where
          -- restrict user/group to posix ^[a-z][-a-z0-9]{0,30}$
          name = do
            first <- choose ('a', 'z')
            rest <- listOf0ToN 30 (oneof [choose ('a', 'z'), choose ('0', '9'), pure '-'])
            return $ first : rest
          idno = arbitraryOctal 7

      shrink (Ownership oname gname oid gid) =
        [ Ownership oname' gname' oid' gid'
        | (oname', gname', oid', gid') <- shrink (oname, gname, oid, gid) ]

    instance Arbitrary Format where
      arbitrary = elements [V7Format, UstarFormat, GnuFormat]

    --arbitraryOctal :: (Integral n, Random n) => Int -> Gen n
    arbitraryOctal n =
        oneof [ pure 0
              , choose (0, upperBound)
              , pure upperBound
              ]
      where
        upperBound = 8^n-1

    -- For QC tests it's useful to have a way to limit the info to that which can
    -- be expressed in the old V7 format
    limitToV7FormatCompat :: Entry -> Entry
    limitToV7FormatCompat entry@Entry { entryFormat = V7Format } =
        entry {
          entryContent = case entryContent entry of
            CharacterDevice _ _ -> OtherEntryType  '3' LBS.empty 0
            BlockDevice     _ _ -> OtherEntryType  '4' LBS.empty 0
            Directory           -> OtherEntryType  '5' LBS.empty 0
            NamedPipe           -> OtherEntryType  '6' LBS.empty 0
            other               -> other,

          entryOwnership = (entryOwnership entry) {
            groupName = "",
            ownerName = ""
          },

          entryTarPath = let TarPath name _prefix = entryTarPath entry
                          in TarPath name BS.empty
        }
    limitToV7FormatCompat entry = entry

    #endif