revlogv2: simplify and clarify the processing of each entry

As we add more entries and some of them has non trivial processing it seems
useful to make the processing leaner and clearly separated to simplify futures
patches.

Differential Revision: https://phab.mercurial-scm.org/D10773

mercurial/revlogutils/docket.py

@@ -1,265 +1,276 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
-    version_header = header[0]
-    index_uuid_size = header[1]
+
+    iheader = iter(header)
+
+    version_header = next(iheader)
+
+    index_uuid_size = next(iheader)
     index_uuid = data[offset : offset + index_uuid_size]
     offset += index_uuid_size
-    data_uuid_size = header[2]
+
+    data_uuid_size = next(iheader)
     data_uuid = data[offset : offset + data_uuid_size]
     offset += data_uuid_size
-    index_size = header[3]
-    pending_index_size = header[4]
-    data_size = header[5]
-    pending_data_size = header[6]
-    default_compression_header = header[7]
+
+    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