text: # revlog.py - storage back-end for mercurial
  #
  # Copyright 2005-2007 Matt Mackall <mpm@selenic.com>
  #
  # This software may be used and distributed according to the terms of the
  # GNU General Public License version 2 or any later version.
  
  """Storage back-end for Mercurial.
  
  This provides efficient delta storage with O(1) retrieve and append
  and O(changes) merge between branches.
  """
  
  # import stuff from node for others to import from revlog
  from node import bin, hex, nullid, nullrev
  from i18n import _
  import ancestor, mdiff, parsers, error, util
  import struct, zlib, errno
  
  _pack = struct.pack
  _unpack = struct.unpack
  _compress = zlib.compress
  _decompress = zlib.decompress
  _sha = util.sha1
  
  # revlog header flags
  REVLOGV0 = 0
  REVLOGNG = 1
  REVLOGNGINLINEDATA = (1 << 16)
  REVLOGGENERALDELTA = (1 << 17)
  REVLOG_DEFAULT_FLAGS = REVLOGNGINLINEDATA
  REVLOG_DEFAULT_FORMAT = REVLOGNG
  REVLOG_DEFAULT_VERSION = REVLOG_DEFAULT_FORMAT | REVLOG_DEFAULT_FLAGS
  REVLOGNG_FLAGS = REVLOGNGINLINEDATA | REVLOGGENERALDELTA
  
  # revlog index flags
  REVIDX_KNOWN_FLAGS = 0
  
  # max size of revlog with inline data
  _maxinline = 131072
  _chunksize = 1048576
  
  RevlogError = error.RevlogError
  LookupError = error.LookupError
  
  def getoffset(q):
      return int(q >> 16)
  
  def gettype(q):
      return int(q & 0xFFFF)
  
  def offset_type(offset, type):
      return long(long(offset) << 16 | type)
  
  nullhash = _sha(nullid)
  
  def hash(text, p1, p2):
      """generate a hash from the given text and its parent hashes
  
      This hash combines both the current file contents and its history
      in a manner that makes it easy to distinguish nodes with the same
      content in the revision graph.
      """
      # As of now, if one of the parent node is null, p2 is null
      if p2 == nullid:
          # deep copy of a hash is faster than creating one
          s = nullhash.copy()
          s.update(p1)
      else:
          # none of the parent nodes are nullid
          l = [p1, p2]
          l.sort()
          s = _sha(l[0])
          s.update(l[1])
      s.update(text)
      return s.digest()
  
  def decompress(bin):
      """ decompress the given input """
      if not bin:
          return bin
      t = bin[0]
      if t == '\0':
          return bin
      if t == 'x':
          try:
              return _decompress(bin)
          except zlib.error, e:
              raise RevlogError(_("revlog decompress error: %s") % str(e))
      if t == 'u':
          return bin[1:]
      raise RevlogError(_("unknown compression type %r") % t)
  
  # index v0:
  #  4 bytes: offset
  #  4 bytes: compressed length
  #  4 bytes: base rev
  #  4 bytes: link rev
  # 32 bytes: parent 1 nodeid
  # 32 bytes: parent 2 nodeid
  # 32 bytes: nodeid
  indexformatv0 = ">4l20s20s20s"
  v0shaoffset = 56
  
  class revlogoldio(object):
      def __init__(self):
          self.size = struct.calcsize(indexformatv0)
  
      def parseindex(self, data, inline):
          s = self.size
          index = []
          nodemap =  {nullid: nullrev}
          n = off = 0
          l = len(data)
          while off + s <= l:
              cur = data[off:off + s]
              off += s
              e = _unpack(indexformatv0, cur)
              # transform to revlogv1 format
              e2 = (offset_type(e[0], 0), e[1], -1, e[2], e[3],
                    nodemap.get(e[4], nullrev), nodemap.get(e[5], nullrev), e[6])
              index.append(e2)
              nodemap[e[6]] = n
              n += 1
  
          # add the magic null revision at -1
          index.append((0, 0, 0, -1, -1, -1, -1, nullid))
  
          return index, nodemap, None
  
      def packentry(self, entry, node, version, rev):
          if gettype(entry[0]):
              raise RevlogError(_("index entry flags need RevlogNG"))
          e2 = (getoffset(entry[0]), entry[1], entry[3], entry[4],
                node(entry[5]), node(entry[6]), entry[7])
          return _pack(indexformatv0, *e2)
  
  # index ng:
  #  6 bytes: offset
  #  2 bytes: flags
  #  4 bytes: compressed length
  #  4 bytes: uncompressed length
  #  4 bytes: base rev
  #  4 bytes: link rev
  #  4 bytes: parent 1 rev
  #  4 bytes: parent 2 rev
  # 32 bytes: nodeid
  indexformatng = ">Qiiiiii20s12x"
  ngshaoffset = 32
  versionformat = ">I"
  
  class revlogio(object):
      def __init__(self):
          self.size = struct.calcsize(indexformatng)
  
      def parseindex(self, data, inline):
          # call the C implementation to parse the index data
          index, cache = parsers.parse_index2(data, inline)
          return index, getattr(index, 'nodemap', None), cache
  
      def packentry(self, entry, node, version, rev):
          p = _pack(indexformatng, *entry)
          if rev == 0:
              p = _pack(versionformat, version) + p[4:]
          return p
  
  class revlog(object):
      """
      the underlying revision storage object
  
      A revlog consists of two parts, an index and the revision data.
  
      The index is a file with a fixed record size containing
      information on each revision, including its nodeid (hash), the
      nodeids of its parents, the position and offset of its data within
      the data file, and the revision it's based on. Finally, each entry
      contains a linkrev entry that can serve as a pointer to external
      data.
  
      The revision data itself is a linear collection of data chunks.
      Each chunk represents a revision and is usually represented as a
      delta against the previous chunk. To bound lookup time, runs of
      deltas are limited to about 2 times the length of the original
      version data. This makes retrieval of a version proportional to
      its size, or O(1) relative to the number of revisions.
  
      Both pieces of the revlog are written to in an append-only
      fashion, which means we never need to rewrite a file to insert or
      remove data, and can use some simple techniques to avoid the need
      for locking while reading.
      """
      def __init__(self, opener, indexfile):
          """
          create a revlog object
  
          opener is a function that abstracts the file opening operation
          and can be used to implement COW semantics or the like.
          """
          self.indexfile = indexfile
          self.datafile = indexfile[:-2] + ".d"
          self.opener = opener
          self._cache = None
          self._basecache = (0, 0)
          self._chunkcache = (0, '')
          self.index = []
          self._pcache = {}
          self._nodecache = {nullid: nullrev}
          self._nodepos = None
  
          v = REVLOG_DEFAULT_VERSION
          opts = getattr(opener, 'options', None)
          if opts is not None:
              if 'revlogv1' in opts:
                  if 'generaldelta' in opts:
                      v |= REVLOGGENERALDELTA
              else:
                  v = 0
  
          i = ''
          self._initempty = True
          try:
              f = self.opener(self.indexfile)
              i = f.read()
              f.close()
              if len(i) > 0:
                  v = struct.unpack(versionformat, i[:4])[0]
                  self._initempty = False
          except IOError, inst:
              if inst.errno != errno.ENOENT:
                  raise
  
          self.version = v
          self._inline = v & REVLOGNGINLINEDATA
          self._generaldelta = v & REVLOGGENERALDELTA
          flags = v & ~0xFFFF
          fmt = v & 0xFFFF
          if fmt == REVLOGV0 and flags:
              raise RevlogError(_("index %s unknown flags %#04x for format v0")
                                % (self.indexfile, flags >> 16))
          elif fmt == REVLOGNG and flags & ~REVLOGNG_FLAGS:
              raise RevlogError(_("index %s unknown flags %#04x for revlogng")
                                % (self.indexfile, flags >> 16))
          elif fmt > REVLOGNG:
              raise RevlogError(_("index %s unknown format %d")
                                % (self.indexfile, fmt))
  
          self._io = revlogio()
          if self.version == REVLOGV0:
              self._io = revlogoldio()
          try:
              d = self._io.parseindex(i, self._inline)
          except (ValueError, IndexError):
              raise RevlogError(_("index %s is corrupted") % (self.indexfile))
          self.index, nodemap, self._chunkcache = d
          if nodemap is not None:
              self.nodemap = self._nodecache = nodemap
          if not self._chunkcache:
              self._chunkclear()
  
      def tip(self):
          return self.node(len(self.index) - 2)
      def __len__(self):
          return len(self.index) - 1
      def __iter__(self):
          return iter(xrange(len(self)))
      def revs(self, start=0, stop=None):
          """iterate over all rev in this revlog (from start to stop)"""
          step = 1
          if stop is not None:
              if start > stop:
                  step = -1
              stop += step
          else:
              stop = len(self)
          return xrange(start, stop, step)
  
      @util.propertycache
      def nodemap(self):
          self.rev(self.node(0))
          return self._nodecache
  
      def hasnode(self, node):
          try:
              self.rev(node)
              return True
          except KeyError:
              return False
  
      def clearcaches(self):
          try:
              self._nodecache.clearcaches()
          except AttributeError:
              self._nodecache = {nullid: nullrev}
              self._nodepos = None
  
      def rev(self, node):
          try:
              return self._nodecache[node]
          except RevlogError:
              # parsers.c radix tree lookup failed
              raise LookupError(node, self.indexfile, _('no node'))
          except KeyError:
              # pure python cache lookup failed
              n = self._nodecache
              i = self.index
              p = self._nodepos
              if p is None:
                  p = len(i) - 2
              for r in xrange(p, -1, -1):
                  v = i[r][7]
                  n[v] = r
                  if v == node:
                      self._nodepos = r - 1
                      return r
              raise LookupError(node, self.indexfile, _('no node'))
  
      def node(self, rev):
          return self.index[rev][7]
      def linkrev(self, rev):
          return self.index[rev][4]
      def parents(self, node):
          i = self.index
          d = i[self.rev(node)]
          return i[d[5]][7], i[d[6]][7] # map revisions to nodes inline
      def parentrevs(self, rev):
          return self.index[rev][5:7]
      def start(self, rev):
          return int(self.index[rev][0] >> 16)
      def end(self, rev):
          return self.start(rev) + self.length(rev)
      def length(self, rev):
          return self.index[rev][1]
      def chainbase(self, rev):
          index = self.index
          base = index[rev][3]
          while base != rev:
              rev = base
              base = index[rev][3]
          return base
      def flags(self, rev):
          return self.index[rev][0] & 0xFFFF
      def rawsize(self, rev):
          """return the length of the uncompressed text for a given revision"""
          l = self.index[rev][2]
          if l >= 0:
              return l
  
          t = self.revision(self.node(rev))
          return len(t)
      size = rawsize
  
      def ancestors(self, revs, stoprev=0, inclusive=False):
          """Generate the ancestors of 'revs' in reverse topological order.
          Does not generate revs lower than stoprev.
  
          See the documentation for ancestor.lazyancestors for more details."""
  
          return ancestor.lazyancestors(self, revs, stoprev=stoprev,
                                        inclusive=inclusive)
  
      def descendants(self, revs):
          """Generate the descendants of 'revs' in revision order.
  
          Yield a sequence of revision numbers starting with a child of
          some rev in revs, i.e., each revision is *not* considered a
          descendant of itself.  Results are ordered by revision number (a
          topological sort)."""
          first = min(revs)
          if first == nullrev:
              for i in self:
                  yield i
              return
  
          seen = set(revs)
          for i in self.revs(start=first + 1):
              for x in self.parentrevs(i):
                  if x != nullrev and x in seen:
                      seen.add(i)
                      yield i
                      break
  
      def findcommonmissing(self, common=None, heads=None):
          """Return a tuple of the ancestors of common and the ancestors of heads
          that are not ancestors of common. In revset terminology, we return the
          tuple:
  
            ::common, (::heads) - (::common)
  
          The list is sorted by revision number, meaning it is
          topologically sorted.
  
          'heads' and 'common' are both lists of node IDs.  If heads is
          not supplied, uses all of the revlog's heads.  If common is not
          supplied, uses nullid."""
          if common is None:
              common = [nullid]
          if heads is None:
              heads = self.heads()
  
          common = [self.rev(n) for n in common]
          heads = [self.rev(n) for n in heads]
  
          # we want the ancestors, but inclusive
          has = set(self.ancestors(common))
          has.add(nullrev)
          has.update(common)
  
          # take all ancestors from heads that aren't in has
          missing = set()
          visit = util.deque(r for r in heads if r not in has)
          while visit:
              r = visit.popleft()
              if r in missing:
                  continue
              else:
                  missing.add(r)
                  for p in self.parentrevs(r):
                      if p not in has:
                          visit.append(p)
          missing = list(missing)
          missing.sort()
          return has, [self.node(r) for r in missing]
  
      def findmissingrevs(self, common=None, heads=None):
          """Return the revision numbers of the ancestors of heads that
          are not ancestors of common.
  
          More specifically, return a list of revision numbers corresponding to
          nodes N such that every N satisfies the following constraints:
  
            1. N is an ancestor of some node in 'heads'
            2. N is not an ancestor of any node in 'common'
  
          The list is sorted by revision number, meaning it is
          topologically sorted.
  
          'heads' and 'common' are both lists of revision numbers.  If heads is
          not supplied, uses all of the revlog's heads.  If common is not
          supplied, uses nullid."""
          if common is None:
              common = [nullrev]
          if heads is None:
              heads = self.headrevs()
  
          return ancestor.missingancestors(heads, common, self.parentrevs)
  
      def findmissing(self, common=None, heads=None):
          """Return the ancestors of heads that are not ancestors of common.
  
          More specifically, return a list of nodes N such that every N
          satisfies the following constraints:
  
            1. N is an ancestor of some node in 'heads'
            2. N is not an ancestor of any node in 'common'
  
          The list is sorted by revision number, meaning it is
          topologically sorted.
  
          'heads' and 'common' are both lists of node IDs.  If heads is
          not supplied, uses all of the revlog's heads.  If common is not
          supplied, uses nullid."""
          if common is None:
              common = [nullid]
          if heads is None:
              heads = self.heads()
  
          common = [self.rev(n) for n in common]
          heads = [self.rev(n) for n in heads]
  
          return [self.node(r) for r in
                  ancestor.missingancestors(heads, common, self.parentrevs)]
  
      def nodesbetween(self, roots=None, heads=None):
          """Return a topological path from 'roots' to 'heads'.
  
          Return a tuple (nodes, outroots, outheads) where 'nodes' is a
          topologically sorted list of all nodes N that satisfy both of
          these constraints:
  
            1. N is a descendant of some node in 'roots'
            2. N is an ancestor of some node in 'heads'
  
          Every node is considered to be both a descendant and an ancestor
          of itself, so every reachable node in 'roots' and 'heads' will be
          included in 'nodes'.
  
          'outroots' is the list of reachable nodes in 'roots', i.e., the
          subset of 'roots' that is returned in 'nodes'.  Likewise,
          'outheads' is the subset of 'heads' that is also in 'nodes'.
  
          'roots' and 'heads' are both lists of node IDs.  If 'roots' is
          unspecified, uses nullid as the only root.  If 'heads' is
          unspecified, uses list of all of the revlog's heads."""
          nonodes = ([], [], [])
          if roots is not None:
              roots = list(roots)
              if not roots:
                  return nonodes
              lowestrev = min([self.rev(n) for n in roots])
          else:
              roots = [nullid] # Everybody's a descendant of nullid
              lowestrev = nullrev
          if (lowestrev == nullrev) and (heads is None):
              # We want _all_ the nodes!
              return ([self.node(r) for r in self], [nullid], list(self.heads()))
          if heads is None:
              # All nodes are ancestors, so the latest ancestor is the last
              # node.
              highestrev = len(self) - 1
              # Set ancestors to None to signal that every node is an ancestor.
              ancestors = None
              # Set heads to an empty dictionary for later discovery of heads
              heads = {}
          else:
              heads = list(heads)
              if not heads:
                  return nonodes
              ancestors = set()
              # Turn heads into a dictionary so we can remove 'fake' heads.
              # Also, later we will be using it to filter out the heads we can't
              # find from roots.
              heads = dict.fromkeys(heads, False)
              # Start at the top and keep marking parents until we're done.
              nodestotag = set(heads)
              # Remember where the top was so we can use it as a limit later.
              highestrev = max([self.rev(n) for n in nodestotag])
              while nodestotag:
                  # grab a node to tag
                  n = nodestotag.pop()
                  # Never tag nullid
                  if n == nullid:
                      continue
                  # A node's revision number represents its place in a
                  # topologically sorted list of nodes.
                  r = self.rev(n)
                  if r >= lowestrev:
                      if n not in ancestors:
                          # If we are possibly a descendant of one of the roots
                          # and we haven't already been marked as an ancestor
                          ancestors.add(n) # Mark as ancestor
                          # Add non-nullid parents to list of nodes to tag.
                          nodestotag.update([p for p in self.parents(n) if
                                             p != nullid])
                      elif n in heads: # We've seen it before, is it a fake head?
                          # So it is, real heads should not be the ancestors of
                          # any other heads.
                          heads.pop(n)
              if not ancestors:
                  return nonodes
              # Now that we have our set of ancestors, we want to remove any
              # roots that are not ancestors.
  
              # If one of the roots was nullid, everything is included anyway.
              if lowestrev > nullrev:
                  # But, since we weren't, let's recompute the lowest rev to not
                  # include roots that aren't ancestors.
  
                  # Filter out roots that aren't ancestors of heads
                  roots = [n for n in roots if n in ancestors]
                  # Recompute the lowest revision
                  if roots:
                      lowestrev = min([self.rev(n) for n in roots])
                  else:
                      # No more roots?  Return empty list
                      return nonodes
              else:
                  # We are descending from nullid, and don't need to care about
                  # any other roots.
                  lowestrev = nullrev
                  roots = [nullid]
          # Transform our roots list into a set.
          descendants = set(roots)
          # Also, keep the original roots so we can filter out roots that aren't
          # 'real' roots (i.e. are descended from other roots).
          roots = descendants.copy()
          # Our topologically sorted list of output nodes.
          orderedout = []
          # Don't start at nullid since we don't want nullid in our output list,
          # and if nullid shows up in descendants, empty parents will look like
          # they're descendants.
          for r in self.revs(start=max(lowestrev, 0), stop=highestrev + 1):
              n = self.node(r)
              isdescendant = False
              if lowestrev == nullrev:  # Everybody is a descendant of nullid
                  isdescendant = True
              elif n in descendants:
                  # n is already a descendant
                  isdescendant = True
                  # This check only needs to be done here because all the roots
                  # will start being marked is descendants before the loop.
                  if n in roots:
                      # If n was a root, check if it's a 'real' root.
                      p = tuple(self.parents(n))
                      # If any of its parents are descendants, it's not a root.
                      if (p[0] in descendants) or (p[1] in descendants):
                          roots.remove(n)
              else:
                  p = tuple(self.parents(n))
                  # A node is a descendant if either of its parents are
                  # descendants.  (We seeded the dependents list with the roots
                  # up there, remember?)
                  if (p[0] in descendants) or (p[1] in descendants):
                      descendants.add(n)
                      isdescendant = True
              if isdescendant and ((ancestors is None) or (n in ancestors)):
                  # Only include nodes that are both descendants and ancestors.
                  orderedout.append(n)
                  if (ancestors is not None) and (n in heads):
                      # We're trying to figure out which heads are reachable
                      # from roots.
                      # Mark this head as having been reached
                      heads[n] = True
                  elif ancestors is None:
                      # Otherwise, we're trying to discover the heads.
                      # Assume this is a head because if it isn't, the next step
                      # will eventually remove it.
                      heads[n] = True
                      # But, obviously its parents aren't.
                      for p in self.parents(n):
                          heads.pop(p, None)
          heads = [n for n, flag in heads.iteritems() if flag]
          roots = list(roots)
          assert orderedout
          assert roots
          assert heads
          return (orderedout, roots, heads)
  
      def headrevs(self):
          try:
              return self.index.headrevs()
          except AttributeError:
              return self._headrevs()
  
      def _headrevs(self):
          count = len(self)
          if not count:
              return [nullrev]
          # we won't iter over filtered rev so nobody is a head at start
          ishead = [0] * (count + 1)
          index = self.index
          for r in self:
              ishead[r] = 1  # I may be an head
              e = index[r]
              ishead[e[5]] = ishead[e[6]] = 0  # my parent are not
          return [r for r, val in enumerate(ishead) if val]
  
      def heads(self, start=None, stop=None):
          """return the list of all nodes that have no children
  
          if start is specified, only heads that are descendants of
          start will be returned
          if stop is specified, it will consider all the revs from stop
          as if they had no children
          """
          if start is None and stop is None:
              if not len(self):
                  return [nullid]
              return [self.node(r) for r in self.headrevs()]
  
          if start is None:
              start = nullid
          if stop is None:
              stop = []
          stoprevs = set([self.rev(n) for n in stop])
          startrev = self.rev(start)
          reachable = set((startrev,))
          heads = set((startrev,))
  
          parentrevs = self.parentrevs
          for r in self.revs(start=startrev + 1):
              for p in parentrevs(r):
                  if p in reachable:
                      if r not in stoprevs:
                          reachable.add(r)
                      heads.add(r)
                  if p in heads and p not in stoprevs:
                      heads.remove(p)
  
          return [self.node(r) for r in heads]
  
      def children(self, node):
          """find the children of a given node"""
          c = []
          p = self.rev(node)
          for r in self.revs(start=p + 1):
              prevs = [pr for pr in self.parentrevs(r) if pr != nullrev]
              if prevs:
                  for pr in prevs:
                      if pr == p:
                          c.append(self.node(r))
              elif p == nullrev:
                  c.append(self.node(r))
          return c
  
      def descendant(self, start, end):
          if start == nullrev:
              return True
          for i in self.descendants([start]):
              if i == end:
                  return True
              elif i > end:
                  break
          return False
  
      def ancestor(self, a, b):
          """calculate the least common ancestor of nodes a and b"""
  
          a, b = self.rev(a), self.rev(b)
          try:
              ancs = self.index.ancestors(a, b)
          except (AttributeError, OverflowError):
              ancs = ancestor.ancestors(self.parentrevs, a, b)
          if ancs:
              # choose a consistent winner when there's a tie
              return min(map(self.node, ancs))
          return nullid
  
      def _match(self, id):
          if isinstance(id, int):
              # rev
              return self.node(id)
          if len(id) == 20:
              # possibly a binary node
              # odds of a binary node being all hex in ASCII are 1 in 10**25
              try:
                  node = id
                  self.rev(node) # quick search the index
                  return node
              except LookupError:
                  pass # may be partial hex id
          try:
              # str(rev)
              rev = int(id)
              if str(rev) != id:
                  raise ValueError
              if rev < 0:
                  rev = len(self) + rev
              if rev < 0 or rev >= len(self):
                  raise ValueError
              return self.node(rev)
          except (ValueError, OverflowError):
              pass
          if len(id) == 40:
              try:
                  # a full hex nodeid?
                  node = bin(id)
                  self.rev(node)
                  return node
              except (TypeError, LookupError):
                  pass
  
      def _partialmatch(self, id):
          try:
              n = self.index.partialmatch(id)
              if n and self.hasnode(n):
                  return n
              return None
          except RevlogError:
              # parsers.c radix tree lookup gave multiple matches
              # fall through to slow path that filters hidden revisions
              pass
          except (AttributeError, ValueError):
              # we are pure python, or key was too short to search radix tree
              pass
  
          if id in self._pcache:
              return self._pcache[id]
  
          if len(id) < 40:
              try:
                  # hex(node)[:...]
                  l = len(id) // 2  # grab an even number of digits
                  prefix = bin(id[:l * 2])
                  nl = [e[7] for e in self.index if e[7].startswith(prefix)]
                  nl = [n for n in nl if hex(n).startswith(id) and
                        self.hasnode(n)]
                  if len(nl) > 0:
                      if len(nl) == 1:
                          self._pcache[id] = nl[0]
                          return nl[0]
                      raise LookupError(id, self.indexfile,
                                        _('ambiguous identifier'))
                  return None
              except TypeError:
                  pass
  
      def lookup(self, id):
          """locate a node based on:
              - revision number or str(revision number)
              - nodeid or subset of hex nodeid
          """
          n = self._match(id)
          if n is not None:
              return n
          n = self._partialmatch(id)
          if n:
              return n
  
          raise LookupError(id, self.indexfile, _('no match found'))
  
      def cmp(self, node, text):
          """compare text with a given file revision
  
          returns True if text is different than what is stored.
          """
          p1, p2 = self.parents(node)
          return hash(text, p1, p2) != node
  
      def _addchunk(self, offset, data):
          o, d = self._chunkcache
          # try to add to existing cache
          if o + len(d) == offset and len(d) + len(data) < _chunksize:
              self._chunkcache = o, d + data
          else:
              self._chunkcache = offset, data
  
      def _loadchunk(self, offset, length):
          if self._inline:
              df = self.opener(self.indexfile)
          else:
              df = self.opener(self.datafile)
  
          readahead = max(65536, length)
          df.seek(offset)
          d = df.read(readahead)
          df.close()
          self._addchunk(offset, d)
          if readahead > length:
              return util.buffer(d, 0, length)
          return d
  
      def _getchunk(self, offset, length):
          o, d = self._chunkcache
          l = len(d)
  
          # is it in the cache?
          cachestart = offset - o
          cacheend = cachestart + length
          if cachestart >= 0 and cacheend <= l:
              if cachestart == 0 and cacheend == l:
                  return d # avoid a copy
              return util.buffer(d, cachestart, cacheend - cachestart)
  
          return self._loadchunk(offset, length)
  
      def _chunkraw(self, startrev, endrev):
          start = self.start(startrev)
          length = self.end(endrev) - start
          if self._inline:
              start += (startrev + 1) * self._io.size
          return self._getchunk(start, length)
  
      def _chunk(self, rev):
          return decompress(self._chunkraw(rev, rev))
  
      def _chunkbase(self, rev):
          return self._chunk(rev)
  
      def _chunkclear(self):
          self._chunkcache = (0, '')
  
      def deltaparent(self, rev):
          """return deltaparent of the given revision"""
          base = self.index[rev][3]
          if base == rev:
              return nullrev
          elif self._generaldelta:
              return base
          else:
              return rev - 1
  
      def revdiff(self, rev1, rev2):
          """return or calculate a delta between two revisions"""
          if rev1 != nullrev and self.deltaparent(rev2) == rev1:
              return str(self._chunk(rev2))
  
          return mdiff.textdiff(self.revision(rev1),
                                self.revision(rev2))
  
      def revision(self, nodeorrev):
          """return an uncompressed revision of a given node or revision
          number.
          """
          if isinstance(nodeorrev, int):
              rev = nodeorrev
              node = self.node(rev)
          else:
              node = nodeorrev
              rev = None
  
          cachedrev = None
          if node == nullid:
              return ""
          if self._cache:
              if self._cache[0] == node:
                  return self._cache[2]
              cachedrev = self._cache[1]
  
          # look up what we need to read
          text = None
          if rev is None:
              rev = self.rev(node)
  
          # check rev flags
          if self.flags(rev) & ~REVIDX_KNOWN_FLAGS:
              raise RevlogError(_('incompatible revision flag %x') %
                                (self.flags(rev) & ~REVIDX_KNOWN_FLAGS))
  
          # build delta chain
          chain = []
          index = self.index # for performance
          generaldelta = self._generaldelta
          iterrev = rev
          e = index[iterrev]
          while iterrev != e[3] and iterrev != cachedrev:
              chain.append(iterrev)
              if generaldelta:
                  iterrev = e[3]
              else:
                  iterrev -= 1
              e = index[iterrev]
          chain.reverse()
          base = iterrev
  
          if iterrev == cachedrev:
              # cache hit
              text = self._cache[2]
  
          # drop cache to save memory
          self._cache = None
  
          self._chunkraw(base, rev)
          if text is None:
              text = str(self._chunkbase(base))
  
          bins = [self._chunk(r) for r in chain]
          text = mdiff.patches(text, bins)
  
          text = self._checkhash(text, node, rev)
  
          self._cache = (node, rev, text)
          return text
  
      def _checkhash(self, text, node, rev):
          p1, p2 = self.parents(node)
          if node != hash(text, p1, p2):
              raise RevlogError(_("integrity check failed on %s:%d")
                                % (self.indexfile, rev))
          return text
  
      def checkinlinesize(self, tr, fp=None):
          if not self._inline or (self.start(-2) + self.length(-2)) < _maxinline:
              return
  
          trinfo = tr.find(self.indexfile)
          if trinfo is None:
              raise RevlogError(_("%s not found in the transaction")
                                % self.indexfile)
  
          trindex = trinfo[2]
          dataoff = self.start(trindex)
  
          tr.add(self.datafile, dataoff)
  
          if fp:
              fp.flush()
              fp.close()
  
          df = self.opener(self.datafile, 'w')
          try:
              for r in self:
                  df.write(self._chunkraw(r, r))
          finally:
              df.close()
  
          fp = self.opener(self.indexfile, 'w', atomictemp=True)
          self.version &= ~(REVLOGNGINLINEDATA)
          self._inline = False
          for i in self:
              e = self._io.packentry(self.index[i], self.node, self.version, i)
              fp.write(e)
  
          # if we don't call close, the temp file will never replace the
          # real index
          fp.close()
  
          tr.replace(self.indexfile, trindex * self._io.size)
          self._chunkclear()
  
      def addrevision(self, text, transaction, link, p1, p2, cachedelta=None):
          """add a revision to the log
  
          text - the revision data to add
          transaction - the transaction object used for rollback
          link - the linkrev data to add
          p1, p2 - the parent nodeids of the revision
          cachedelta - an optional precomputed delta
          """
          if link == nullrev:
              raise RevlogError(_("attempted to add linkrev -1 to %s")
                                % self.indexfile)
          node = hash(text, p1, p2)
          if node in self.nodemap:
              return node
  
          dfh = None
          if not self._inline:
              dfh = self.opener(self.datafile, "a")
          ifh = self.opener(self.indexfile, "a+")
          try:
              return self._addrevision(node, text, transaction, link, p1, p2,
                                       cachedelta, ifh, dfh)
          finally:
              if dfh:
                  dfh.close()
              ifh.close()
  
      def compress(self, text):
          """ generate a possibly-compressed representation of text """
          if not text:
              return ("", text)
          l = len(text)
          bin = None
          if l < 44:
              pass
          elif l > 1000000:
              # zlib makes an internal copy, thus doubling memory usage for
              # large files, so lets do this in pieces
              z = zlib.compressobj()
              p = []
              pos = 0
              while pos < l:
                  pos2 = pos + 2**20
                  p.append(z.compress(text[pos:pos2]))
                  pos = pos2
              p.append(z.flush())
              if sum(map(len, p)) < l:
                  bin = "".join(p)
          else:
              bin = _compress(text)
          if bin is None or len(bin) > l:
              if text[0] == '\0':
                  return ("", text)
              return ('u', text)
          return ("", bin)
  
      def _addrevision(self, node, text, transaction, link, p1, p2,
                       cachedelta, ifh, dfh):
          """internal function to add revisions to the log
  
          see addrevision for argument descriptions.
          invariants:
          - text is optional (can be None); if not set, cachedelta must be set.
            if both are set, they must correspond to each other.
          """
          btext = [text]
          def buildtext():
              if btext[0] is not None:
                  return btext[0]
              # flush any pending writes here so we can read it in revision
              if dfh:
                  dfh.flush()
              ifh.flush()
              basetext = self.revision(self.node(cachedelta[0]))
              btext[0] = mdiff.patch(basetext, cachedelta[1])
              chk = hash(btext[0], p1, p2)
              if chk != node:
                  raise RevlogError(_("consistency error in delta"))
              return btext[0]
  
          def builddelta(rev):
              # can we use the cached delta?
              if cachedelta and cachedelta[0] == rev:
                  delta = cachedelta[1]
              else:
                  t = buildtext()
                  ptext = self.revision(self.node(rev))
                  delta = mdiff.textdiff(ptext, t)
              data = self.compress(delta)
              l = len(data[1]) + len(data[0])
              if basecache[0] == rev:
                  chainbase = basecache[1]
              else:
                  chainbase = self.chainbase(rev)
              dist = l + offset - self.start(chainbase)
              if self._generaldelta:
                  base = rev
              else:
                  base = chainbase
              return dist, l, data, base, chainbase
  
          curr = len(self)
          prev = curr - 1
          base = chainbase = curr
          offset = self.end(prev)
          flags = 0
          d = None
          basecache = self._basecache
          p1r, p2r = self.rev(p1), self.rev(p2)
  
          # should we try to build a delta?
          if prev != nullrev:
              if self._generaldelta:
                  if p1r >= basecache[1]:
                      d = builddelta(p1r)
                  elif p2r >= basecache[1]:
                      d = builddelta(p2r)
                  else:
                      d = builddelta(prev)
              else:
                  d = builddelta(prev)
              dist, l, data, base, chainbase = d
  
          # full versions are inserted when the needed deltas
          # become comparable to the uncompressed text
          if text is None:
              textlen = mdiff.patchedsize(self.rawsize(cachedelta[0]),
                                          cachedelta[1])
          else:
              textlen = len(text)
          if d is None or dist > textlen * 2:
              text = buildtext()
              data = self.compress(text)
              l = len(data[1]) + len(data[0])
              base = chainbase = curr
  
          e = (offset_type(offset, flags), l, textlen,
               base, link, p1r, p2r, node)
          self.index.insert(-1, e)
          self.nodemap[node] = curr
  
          entry = self._io.packentry(e, self.node, self.version, curr)
          if not self._inline:
              transaction.add(self.datafile, offset)
              transaction.add(self.indexfile, curr * len(entry))
              if data[0]:
                  dfh.write(data[0])
              dfh.write(data[1])
              dfh.flush()
              ifh.write(entry)
          else:
              offset += curr * self._io.size
              transaction.add(self.indexfile, offset, curr)
              ifh.write(entry)
              ifh.write(data[0])
              ifh.write(data[1])
              self.checkinlinesize(transaction, ifh)
  
          if type(text) == str: # only accept immutable objects
              self._cache = (node, curr, text)
          self._basecache = (curr, chainbase)
          return node
  
      def addgroup(self, bundle, linkmapper, transaction):
          """
          add a delta group
  
          given a set of deltas, add them to the revision log. the
          first delta is against its parent, which should be in our
          log, the rest are against the previous delta.
          """
  
          # track the base of the current delta log
          content = []
          node = None
  
          r = len(self)
          end = 0
          if r:
              end = self.end(r - 1)
          ifh = self.opener(self.indexfile, "a+")
          isize = r * self._io.size
          if self._inline:
              transaction.add(self.indexfile, end + isize, r)
              dfh = None
          else:
              transaction.add(self.indexfile, isize, r)
              transaction.add(self.datafile, end)
              dfh = self.opener(self.datafile, "a")
  
          try:
              # loop through our set of deltas
              chain = None
              while True:
                  chunkdata = bundle.deltachunk(chain)
                  if not chunkdata:
                      break
                  node = chunkdata['node']
                  p1 = chunkdata['p1']
                  p2 = chunkdata['p2']
                  cs = chunkdata['cs']
                  deltabase = chunkdata['deltabase']
                  delta = chunkdata['delta']
  
                  content.append(node)
  
                  link = linkmapper(cs)
                  if node in self.nodemap:
                      # this can happen if two branches make the same change
                      chain = node
                      continue
  
                  for p in (p1, p2):
                      if p not in self.nodemap:
                          raise LookupError(p, self.indexfile,
                                            _('unknown parent'))
  
                  if deltabase not in self.nodemap:
                      raise LookupError(deltabase, self.indexfile,
                                        _('unknown delta base'))
  
                  baserev = self.rev(deltabase)
                  chain = self._addrevision(node, None, transaction, link,
                                            p1, p2, (baserev, delta), ifh, dfh)
                  if not dfh and not self._inline:
                      # addrevision switched from inline to conventional
                      # reopen the index
                      ifh.close()
                      dfh = self.opener(self.datafile, "a")
                      ifh = self.opener(self.indexfile, "a")
          finally:
              if dfh:
                  dfh.close()
              ifh.close()
  
          return content
  
      def strip(self, minlink, transaction):
          """truncate the revlog on the first revision with a linkrev >= minlink
  
          This function is called when we're stripping revision minlink and
          its descendants from the repository.
  
          We have to remove all revisions with linkrev >= minlink, because
          the equivalent changelog revisions will be renumbered after the
          strip.
  
          So we truncate the revlog on the first of these revisions, and
          trust that the caller has saved the revisions that shouldn't be
          removed and that it'll re-add them after this truncation.
          """
          if len(self) == 0:
              return
  
          for rev in self:
              if self.index[rev][4] >= minlink:
                  break
          else:
              return
  
          # first truncate the files on disk
          end = self.start(rev)
          if not self._inline:
              transaction.add(self.datafile, end)
              end = rev * self._io.size
          else:
              end += rev * self._io.size
  
          transaction.add(self.indexfile, end)
  
          # then reset internal state in memory to forget those revisions
          self._cache = None
          self._chunkclear()
          for x in xrange(rev, len(self)):
              del self.nodemap[self.node(x)]
  
          del self.index[rev:-1]
  
      def checksize(self):
          expected = 0
          if len(self):
              expected = max(0, self.end(len(self) - 1))
  
          try:
              f = self.opener(self.datafile)
              f.seek(0, 2)
              actual = f.tell()
              f.close()
              dd = actual - expected
          except IOError, inst:
              if inst.errno != errno.ENOENT:
                  raise
              dd = 0
  
          try:
              f = self.opener(self.indexfile)
              f.seek(0, 2)
              actual = f.tell()
              f.close()
              s = self._io.size
              i = max(0, actual // s)
              di = actual - (i * s)
              if self._inline:
                  databytes = 0
                  for r in self:
                      databytes += max(0, self.length(r))
                  dd = 0
                  di = actual - len(self) * s - databytes
          except IOError, inst:
              if inst.errno != errno.ENOENT:
                  raise
              di = 0
  
          return (dd, di)
  
      def files(self):
          res = [self.indexfile]
          if not self._inline:
              res.append(self.datafile)
          return res
  