revlogv2: add a `get_data` helper to grab the next piece of docket

This make the processing more compact but abstracting repetitive processing
away.

Differential Revision: https://phab.mercurial-scm.org/D10774

mercurial/revlogutils/docket.py

@@ -1,276 +1,287 b''
 # docket - code related to revlog "docket"
 #
 # Copyright 2021 Pierre-Yves David <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 ### Revlog docket file
 #
 # The revlog is stored on disk using multiple files:
 #
 # * a small docket file, containing metadata and a pointer,
 #
 # * an index file, containing fixed width information about revisions,
 #
 # * a data file, containing variable width data for these revisions,
 
 from __future__ import absolute_import
 
 import errno
 import os
 import random
 import struct
 
 from .. import (
     encoding,
     error,
     node,
     pycompat,
     util,
 )
 
 from . import (
     constants,
 )
 
 
 def make_uid(id_size=8):
     """return a new unique identifier.
 
     The identifier is random and composed of ascii characters."""
     # size we "hex" the result we need half the number of bits to have a final
     # uuid of size ID_SIZE
     return node.hex(os.urandom(id_size // 2))
 
 
 # some special test logic to avoid anoying random output in the test
 stable_docket_file = encoding.environ.get(b'HGTEST_UUIDFILE')
 
 if stable_docket_file:
 
     def make_uid(id_size=8):
         try:
             with open(stable_docket_file, mode='rb') as f:
                 seed = f.read().strip()
         except IOError as inst:
             if inst.errno != errno.ENOENT:
                 raise
             seed = b'04'  # chosen by a fair dice roll. garanteed to be random
         if pycompat.ispy3:
             iter_seed = iter(seed)
         else:
             iter_seed = (ord(c) for c in seed)
         # some basic circular sum hashing on 64 bits
         int_seed = 0
         low_mask = int('1' * 35, 2)
         for i in iter_seed:
             high_part = int_seed >> 35
             low_part = (int_seed & low_mask) << 28
             int_seed = high_part + low_part + i
         r = random.Random()
         if pycompat.ispy3:
             r.seed(int_seed, version=1)
         else:
             r.seed(int_seed)
         # once we drop python 3.8 support we can simply use r.randbytes
         raw = r.getrandbits(id_size * 4)
         assert id_size == 8
         p = struct.pack('>L', raw)
         new = node.hex(p)
         with open(stable_docket_file, 'wb') as f:
             f.write(new)
         return new
 
 
 # Docket format
 #
 # * 4 bytes: revlog version
 #          |   This is mandatory as docket must be compatible with the previous
 #          |   revlog index header.
 # * 1 bytes: size of index uuid
 # * 1 bytes: size of data uuid
 # * 8 bytes: size of index-data
 # * 8 bytes: pending size of index-data
 # * 8 bytes: size of data
 # * 8 bytes: pending size of data
 # * 1 bytes: default compression header
 S_HEADER = struct.Struct(constants.INDEX_HEADER.format + 'BBLLLLc')
 
 
 class RevlogDocket(object):
     """metadata associated with revlog"""
 
     def __init__(
         self,
         revlog,
         use_pending=False,
         version_header=None,
         index_uuid=None,
         data_uuid=None,
         index_end=0,
         pending_index_end=0,
         data_end=0,
         pending_data_end=0,
         default_compression_header=None,
     ):
         self._version_header = version_header
         self._read_only = bool(use_pending)
         self._dirty = False
         self._radix = revlog.radix
         self._path = revlog._docket_file
         self._opener = revlog.opener
         self._index_uuid = index_uuid
         self._data_uuid = data_uuid
         # thes asserts should be True as long as we have a single index filename
         assert index_end <= pending_index_end
         assert data_end <= pending_data_end
         self._initial_index_end = index_end
         self._pending_index_end = pending_index_end
         self._initial_data_end = data_end
         self._pending_data_end = pending_data_end
         if use_pending:
             self._index_end = self._pending_index_end
             self._data_end = self._pending_data_end
         else:
             self._index_end = self._initial_index_end
             self._data_end = self._initial_data_end
         self.default_compression_header = default_compression_header
 
     def index_filepath(self):
         """file path to the current index file associated to this docket"""
         # very simplistic version at first
         if self._index_uuid is None:
             self._index_uuid = make_uid()
         return b"%s-%s.idx" % (self._radix, self._index_uuid)
 
     def data_filepath(self):
         """file path to the current index file associated to this docket"""
         # very simplistic version at first
         if self._data_uuid is None:
             self._data_uuid = make_uid()
         return b"%s-%s.dat" % (self._radix, self._data_uuid)
 
     @property
     def index_end(self):
         return self._index_end
 
     @index_end.setter
     def index_end(self, new_size):
         if new_size != self._index_end:
             self._index_end = new_size
             self._dirty = True
 
     @property
     def data_end(self):
         return self._data_end
 
     @data_end.setter
     def data_end(self, new_size):
         if new_size != self._data_end:
             self._data_end = new_size
             self._dirty = True
 
     def write(self, transaction, pending=False, stripping=False):
         """write the modification of disk if any
 
         This make the new content visible to all process"""
         if not self._dirty:
             return False
         else:
             if self._read_only:
                 msg = b'writing read-only docket: %s'
                 msg %= self._path
                 raise error.ProgrammingError(msg)
             if not stripping:
                 # XXX we could, leverage the docket while stripping. However it
                 # is not powerfull enough at the time of this comment
                 transaction.addbackup(self._path, location=b'store')
             with self._opener(self._path, mode=b'w', atomictemp=True) as f:
                 f.write(self._serialize(pending=pending))
             # if pending we still need to the write final data eventually
             self._dirty = pending
             return True
 
     def _serialize(self, pending=False):
         if pending:
             official_index_end = self._initial_index_end
             official_data_end = self._initial_data_end
         else:
             official_index_end = self._index_end
             official_data_end = self._data_end
 
         # this assert should be True as long as we have a single index filename
         assert official_data_end <= self._data_end
         data = (
             self._version_header,
             len(self._index_uuid),
             len(self._data_uuid),
             official_index_end,
             self._index_end,
             official_data_end,
             self._data_end,
             self.default_compression_header,
         )
         s = []
         s.append(S_HEADER.pack(*data))
         s.append(self._index_uuid)
         s.append(self._data_uuid)
         return b''.join(s)
 
 
 def default_docket(revlog, version_header):
     """given a revlog version a new docket object for the given revlog"""
     rl_version = version_header & 0xFFFF
     if rl_version not in (constants.REVLOGV2, constants.CHANGELOGV2):
         return None
     comp = util.compengines[revlog._compengine].revlogheader()
     docket = RevlogDocket(
         revlog,
         version_header=version_header,
         default_compression_header=comp,
     )
     docket._dirty = True
     return docket
 
 
 def parse_docket(revlog, data, use_pending=False):
     """given some docket data return a docket object for the given revlog"""
     header = S_HEADER.unpack(data[: S_HEADER.size])
-    offset = S_HEADER.size
+
+    # this is a mutable closure capture used in `get_data`
+    offset = [S_HEADER.size]
+
+    def get_data(size):
+        """utility closure to access the `size` next bytes"""
+        if offset[0] + size > len(data):
+            # XXX better class
+            msg = b"docket is too short, expected %d got %d"
+            msg %= (offset[0] + size, len(data))
+            raise error.Abort(msg)
+        raw = data[offset[0] : offset[0] + size]
+        offset[0] += size
+        return raw
 
     iheader = iter(header)
 
     version_header = next(iheader)
 
     index_uuid_size = next(iheader)
-    index_uuid = data[offset : offset + index_uuid_size]
-    offset += index_uuid_size
+    index_uuid = get_data(index_uuid_size)
 
     data_uuid_size = next(iheader)
-    data_uuid = data[offset : offset + data_uuid_size]
-    offset += data_uuid_size
+    data_uuid = get_data(data_uuid_size)
 
     index_size = next(iheader)
 
     pending_index_size = next(iheader)
 
     data_size = next(iheader)
 
     pending_data_size = next(iheader)
 
     default_compression_header = next(iheader)
 
     docket = RevlogDocket(
         revlog,
         use_pending=use_pending,
         version_header=version_header,
         index_uuid=index_uuid,
         data_uuid=data_uuid,
         index_end=index_size,
         pending_index_end=pending_index_size,
         data_end=data_size,
         pending_data_end=pending_data_size,
         default_compression_header=default_compression_header,
     )
     return docket