mercurial/revlogutils/constants.py

revlog: move the details of revlog "v0" index inside revlog.utils.constants

the revlog module is quite large and this kind of format information would handy
for other module. So let us start to gather this information about the format in
a more appropriate place.

Differential Revision: https://phab.mercurial-scm.org/D10303

# revlogdeltas.py - constant used for revlog logic
#
# Copyright 2005-2007 Olivia Mackall <[e-mail]>
# Copyright 2018 Octobus <[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.
"""Helper class to compute deltas stored inside revlogs"""

from __future__ import absolute_import

import struct

from ..interfaces import repository

### main revlog header

## revlog version
REVLOGV0 = 0
REVLOGV1 = 1
# Dummy value until file format is finalized.
REVLOGV2 = 0xDEAD

##  global revlog header flags
# Shared across v1 and v2.
FLAG_INLINE_DATA = 1 << 16
# Only used by v1, implied by v2.
FLAG_GENERALDELTA = 1 << 17
REVLOG_DEFAULT_FLAGS = FLAG_INLINE_DATA
REVLOG_DEFAULT_FORMAT = REVLOGV1
REVLOG_DEFAULT_VERSION = REVLOG_DEFAULT_FORMAT | REVLOG_DEFAULT_FLAGS
REVLOGV1_FLAGS = FLAG_INLINE_DATA | FLAG_GENERALDELTA
REVLOGV2_FLAGS = FLAG_INLINE_DATA

### individual entry

## index v0:
#  4 bytes: offset
#  4 bytes: compressed length
#  4 bytes: base rev
#  4 bytes: link rev
# 20 bytes: parent 1 nodeid
# 20 bytes: parent 2 nodeid
# 20 bytes: nodeid
INDEX_ENTRY_V0 = struct.Struct(b">4l20s20s20s")

# revlog index flags

# For historical reasons, revlog's internal flags were exposed via the
# wire protocol and are even exposed in parts of the storage APIs.

# revision has censor metadata, must be verified
REVIDX_ISCENSORED = repository.REVISION_FLAG_CENSORED
# revision hash does not match data (narrowhg)
REVIDX_ELLIPSIS = repository.REVISION_FLAG_ELLIPSIS
# revision data is stored externally
REVIDX_EXTSTORED = repository.REVISION_FLAG_EXTSTORED
# revision data contains extra metadata not part of the official digest
REVIDX_SIDEDATA = repository.REVISION_FLAG_SIDEDATA
# revision changes files in a way that could affect copy tracing.
REVIDX_HASCOPIESINFO = repository.REVISION_FLAG_HASCOPIESINFO
REVIDX_DEFAULT_FLAGS = 0
# stable order in which flags need to be processed and their processors applied
REVIDX_FLAGS_ORDER = [
    REVIDX_ISCENSORED,
    REVIDX_ELLIPSIS,
    REVIDX_EXTSTORED,
    REVIDX_SIDEDATA,
    REVIDX_HASCOPIESINFO,
]

# bitmark for flags that could cause rawdata content change
REVIDX_RAWTEXT_CHANGING_FLAGS = (
    REVIDX_ISCENSORED | REVIDX_EXTSTORED | REVIDX_SIDEDATA
)

SPARSE_REVLOG_MAX_CHAIN_LENGTH = 1000