mercurial/revlogutils/rewrite.py

censor: extract the part about writing the censored revision in a function

The v2_censor function is huge, now that its content has settled a bit it is a
good time to split individual part inside dedicated function. We start with a
small function that process the censored revision.

Differential Revision: https://phab.mercurial-scm.org/D10898

# censor code related to censoring revision
# coding: utf8
#
# Copyright 2021 Pierre-Yves David <[e-mail]>
# Copyright 2015 Google, Inc <[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.

import contextlib
import os

from ..node import (
    nullrev,
)
from .constants import (
    COMP_MODE_PLAIN,
    ENTRY_DATA_COMPRESSED_LENGTH,
    ENTRY_DATA_COMPRESSION_MODE,
    ENTRY_DATA_OFFSET,
    ENTRY_DATA_UNCOMPRESSED_LENGTH,
    ENTRY_DELTA_BASE,
    ENTRY_LINK_REV,
    ENTRY_NODE_ID,
    ENTRY_PARENT_1,
    ENTRY_PARENT_2,
    ENTRY_SIDEDATA_COMPRESSED_LENGTH,
    ENTRY_SIDEDATA_COMPRESSION_MODE,
    ENTRY_SIDEDATA_OFFSET,
    REVLOGV0,
    REVLOGV1,
)
from ..i18n import _

from .. import (
    error,
    pycompat,
    revlogutils,
    util,
)
from ..utils import (
    storageutil,
)
from . import (
    constants,
    deltas,
)


def v1_censor(rl, tr, censornode, tombstone=b''):
    """censors a revision in a "version 1" revlog"""
    assert rl._format_version == constants.REVLOGV1, rl._format_version

    # avoid cycle
    from .. import revlog

    censorrev = rl.rev(censornode)
    tombstone = storageutil.packmeta({b'censored': tombstone}, b'')

    # Rewriting the revlog in place is hard. Our strategy for censoring is
    # to create a new revlog, copy all revisions to it, then replace the
    # revlogs on transaction close.
    #
    # This is a bit dangerous. We could easily have a mismatch of state.
    newrl = revlog.revlog(
        rl.opener,
        target=rl.target,
        radix=rl.radix,
        postfix=b'tmpcensored',
        censorable=True,
    )
    newrl._format_version = rl._format_version
    newrl._format_flags = rl._format_flags
    newrl._generaldelta = rl._generaldelta
    newrl._parse_index = rl._parse_index

    for rev in rl.revs():
        node = rl.node(rev)
        p1, p2 = rl.parents(node)

        if rev == censorrev:
            newrl.addrawrevision(
                tombstone,
                tr,
                rl.linkrev(censorrev),
                p1,
                p2,
                censornode,
                constants.REVIDX_ISCENSORED,
            )

            if newrl.deltaparent(rev) != nullrev:
                m = _(b'censored revision stored as delta; cannot censor')
                h = _(
                    b'censoring of revlogs is not fully implemented;'
                    b' please report this bug'
                )
                raise error.Abort(m, hint=h)
            continue

        if rl.iscensored(rev):
            if rl.deltaparent(rev) != nullrev:
                m = _(
                    b'cannot censor due to censored '
                    b'revision having delta stored'
                )
                raise error.Abort(m)
            rawtext = rl._chunk(rev)
        else:
            rawtext = rl.rawdata(rev)

        newrl.addrawrevision(
            rawtext, tr, rl.linkrev(rev), p1, p2, node, rl.flags(rev)
        )

    tr.addbackup(rl._indexfile, location=b'store')
    if not rl._inline:
        tr.addbackup(rl._datafile, location=b'store')

    rl.opener.rename(newrl._indexfile, rl._indexfile)
    if not rl._inline:
        rl.opener.rename(newrl._datafile, rl._datafile)

    rl.clearcaches()
    rl._loadindex()


def v2_censor(rl, tr, censornode, tombstone=b''):
    """censors a revision in a "version 2" revlog"""
    # General principle
    #
    # We create new revlog files (index/data/sidedata) to copy the content of
    # the existing data without the censored data.
    #
    # We need to recompute new delta for any revision that used the censored
    # revision as delta base. As the cumulative size of the new delta may be
    # large, we store them in a temporary file until they are stored in their
    # final destination.
    #
    # All data before the censored data can be blindly copied. The rest needs
    # to be copied as we go and the associated index entry needs adjustement.

    assert rl._format_version != REVLOGV0, rl._format_version
    assert rl._format_version != REVLOGV1, rl._format_version

    old_index = rl.index
    docket = rl._docket

    censor_rev = rl.rev(censornode)
    tombstone = storageutil.packmeta({b'censored': tombstone}, b'')

    censored_entry = rl.index[censor_rev]
    index_cutoff = rl.index.entry_size * censor_rev
    data_cutoff = censored_entry[ENTRY_DATA_OFFSET] >> 16
    sidedata_cutoff = rl.sidedata_cut_off(censor_rev)

    # rev → (new_base, data_start, data_end)
    rewritten_entries = {}

    dc = deltas.deltacomputer(rl)
    excl = [censor_rev]

    with pycompat.unnamedtempfile(mode=b"w+b") as tmp_storage:
        with rl._segmentfile._open_read() as dfh:
            for rev in range(censor_rev + 1, len(old_index)):
                entry = old_index[rev]
                if censor_rev != entry[ENTRY_DELTA_BASE]:
                    continue
                # This is a revision that use the censored revision as the base
                # for its delta. We need a need new deltas
                if entry[ENTRY_DATA_UNCOMPRESSED_LENGTH] == 0:
                    # this revision is empty, we can delta against nullrev
                    rewritten_entries[rev] = (nullrev, 0, 0)
                else:

                    text = rl.rawdata(rev, _df=dfh)
                    info = revlogutils.revisioninfo(
                        node=entry[ENTRY_NODE_ID],
                        p1=rl.node(entry[ENTRY_PARENT_1]),
                        p2=rl.node(entry[ENTRY_PARENT_2]),
                        btext=[text],
                        textlen=len(text),
                        cachedelta=None,
                        flags=entry[ENTRY_DATA_OFFSET] & 0xFFFF,
                    )
                    d = dc.finddeltainfo(
                        info, dfh, excluded_bases=excl, target_rev=rev
                    )
                    default_comp = rl._docket.default_compression_header
                    comp_mode, d = deltas.delta_compression(default_comp, d)
                    # using `tell` is a bit lazy, but we are not here for speed
                    start = tmp_storage.tell()
                    tmp_storage.write(d.data[1])
                    end = tmp_storage.tell()
                    rewritten_entries[rev] = (d.base, start, end, comp_mode)

        old_index_filepath = rl.opener.join(docket.index_filepath())
        old_data_filepath = rl.opener.join(docket.data_filepath())
        old_sidedata_filepath = rl.opener.join(docket.sidedata_filepath())

        new_index_filepath = rl.opener.join(docket.new_index_file())
        new_data_filepath = rl.opener.join(docket.new_data_file())
        new_sidedata_filepath = rl.opener.join(docket.new_sidedata_file())

        util.copyfile(
            old_index_filepath, new_index_filepath, nb_bytes=index_cutoff
        )
        util.copyfile(
            old_data_filepath, new_data_filepath, nb_bytes=data_cutoff
        )
        util.copyfile(
            old_sidedata_filepath,
            new_sidedata_filepath,
            nb_bytes=sidedata_cutoff,
        )
        rl.opener.register_file(docket.index_filepath())
        rl.opener.register_file(docket.data_filepath())
        rl.opener.register_file(docket.sidedata_filepath())

        docket.index_end = index_cutoff
        docket.data_end = data_cutoff
        docket.sidedata_end = sidedata_cutoff

        # reload the revlog internal information
        rl.clearcaches()
        rl._loadindex(docket=docket)

        @contextlib.contextmanager
        def all_files():
            # hide opening in an helper function to please check-code, black
            # and various python ersion at the same time
            with open(old_data_filepath, 'rb') as old_data_file:
                with open(old_sidedata_filepath, 'rb') as old_sidedata_file:
                    with open(new_index_filepath, 'r+b') as new_index_file:
                        with open(new_data_filepath, 'r+b') as new_data_file:
                            with open(
                                new_sidedata_filepath, 'r+b'
                            ) as new_sidedata_file:
                                yield (
                                    old_data_file,
                                    old_sidedata_file,
                                    new_index_file,
                                    new_data_file,
                                    new_sidedata_file,
                                )

        # we dont need to open the old index file since its content already
        # exist in a usable form in `old_index`.
        with all_files() as open_files:
            (
                old_data_file,
                old_sidedata_file,
                new_index_file,
                new_data_file,
                new_sidedata_file,
            ) = open_files
            new_index_file.seek(0, os.SEEK_END)
            assert new_index_file.tell() == index_cutoff
            new_data_file.seek(0, os.SEEK_END)
            assert new_data_file.tell() == data_cutoff
            new_sidedata_file.seek(0, os.SEEK_END)
            assert new_sidedata_file.tell() == sidedata_cutoff

            # writing the censored revision
            _rewrite_censor(
                rl,
                old_index,
                open_files,
                censor_rev,
                tombstone,
            )

            #### Writing all subsequent revisions
            for rev in range(censor_rev + 1, len(old_index)):
                entry = old_index[rev]
                flags = entry[ENTRY_DATA_OFFSET] & 0xFFFF
                old_data_offset = entry[ENTRY_DATA_OFFSET] >> 16

                if rev not in rewritten_entries:
                    old_data_file.seek(old_data_offset)
                    new_data_size = entry[ENTRY_DATA_COMPRESSED_LENGTH]
                    new_data = old_data_file.read(new_data_size)
                    data_delta_base = entry[ENTRY_DELTA_BASE]
                    d_comp_mode = entry[ENTRY_DATA_COMPRESSION_MODE]
                else:
                    (
                        data_delta_base,
                        start,
                        end,
                        d_comp_mode,
                    ) = rewritten_entries[rev]
                    new_data_size = end - start
                    tmp_storage.seek(start)
                    new_data = tmp_storage.read(new_data_size)

                # It might be faster to group continuous read/write operation,
                # however, this is censor, an operation that is not focussed
                # around stellar performance. So I have not written this
                # optimisation yet.
                new_data_offset = new_data_file.tell()
                new_data_file.write(new_data)

                sidedata_size = entry[ENTRY_SIDEDATA_COMPRESSED_LENGTH]
                new_sidedata_offset = new_sidedata_file.tell()
                if 0 < sidedata_size:
                    old_sidedata_offset = entry[ENTRY_SIDEDATA_OFFSET]
                    old_sidedata_file.seek(old_sidedata_offset)
                    new_sidedata = old_sidedata_file.read(sidedata_size)
                    new_sidedata_file.write(new_sidedata)

                data_uncompressed_length = entry[ENTRY_DATA_UNCOMPRESSED_LENGTH]
                sd_com_mode = entry[ENTRY_SIDEDATA_COMPRESSION_MODE]
                assert data_delta_base <= rev, (data_delta_base, rev)

                new_entry = revlogutils.entry(
                    flags=flags,
                    data_offset=new_data_offset,
                    data_compressed_length=new_data_size,
                    data_uncompressed_length=data_uncompressed_length,
                    data_delta_base=data_delta_base,
                    link_rev=entry[ENTRY_LINK_REV],
                    parent_rev_1=entry[ENTRY_PARENT_1],
                    parent_rev_2=entry[ENTRY_PARENT_2],
                    node_id=entry[ENTRY_NODE_ID],
                    sidedata_offset=new_sidedata_offset,
                    sidedata_compressed_length=sidedata_size,
                    data_compression_mode=d_comp_mode,
                    sidedata_compression_mode=sd_com_mode,
                )
                rl.index.append(new_entry)
                entry_bin = rl.index.entry_binary(rev)
                new_index_file.write(entry_bin)

                docket.index_end = new_index_file.tell()
                docket.data_end = new_data_file.tell()
                docket.sidedata_end = new_sidedata_file.tell()

    docket.write(transaction=None, stripping=True)


def _rewrite_censor(
    revlog,
    old_index,
    all_files,
    rev,
    tombstone,
):
    """rewrite and append a censored revision"""
    (
        old_data_file,
        old_sidedata_file,
        new_index_file,
        new_data_file,
        new_sidedata_file,
    ) = all_files
    entry = old_index[rev]

    # XXX consider trying the default compression too
    new_data_size = len(tombstone)
    new_data_offset = new_data_file.tell()
    new_data_file.write(tombstone)

    # we are not adding any sidedata as they might leak info about the censored version

    link_rev = entry[ENTRY_LINK_REV]

    p1 = entry[ENTRY_PARENT_1]
    p2 = entry[ENTRY_PARENT_2]

    new_entry = revlogutils.entry(
        flags=constants.REVIDX_ISCENSORED,
        data_offset=new_data_offset,
        data_compressed_length=new_data_size,
        data_uncompressed_length=new_data_size,
        data_delta_base=rev,
        link_rev=link_rev,
        parent_rev_1=p1,
        parent_rev_2=p2,
        node_id=entry[ENTRY_NODE_ID],
        sidedata_offset=0,
        sidedata_compressed_length=0,
        data_compression_mode=COMP_MODE_PLAIN,
        sidedata_compression_mode=COMP_MODE_PLAIN,
    )
    revlog.index.append(new_entry)
    entry_bin = revlog.index.entry_binary(rev)
    new_index_file.write(entry_bin)
    revlog._docket.index_end = new_index_file.tell()
    revlog._docket.data_end = new_data_file.tell()