comparison mercurial/filelog.py @ 24255:4bfe9f2d9761

revlog: addgroup checks if incoming deltas add censored revs, sets flag bit

A censored revision stored in a revlog should have the censored revlog index
flag bit set. This implies we must know if a revision is censored before we
add it to the revlog. When adding revisions from exchanged deltas, we would
prefer to determine this flag without decoding every single full text.

This change introduces a heuristic based on assumptions around the Mercurial
delta format and filelog metadata. Since deltas which produce a censored
revision must be full-replacement deltas, we can read the delta's first bytes
to check the filelog metadata. Since "censored" is the alphabetically first
filelog metadata key, censored filelog revisions have a well-known prefix we
can look for.

For more on the design and background of the censorship feature, see:
http://mercurial.selenic.com/wiki/CensorPlan

24254:60c279ab7bd3

# Copyright 2005-2007 Matt Mackall <[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 error, revlog
import re

_mdre = re.compile('\1\n')
def parsemeta(text):
    """return (metadatadict, keylist, metadatasize)"""
    # text can be buffer, so we can't use .startswith or .index

            raise

    def iscensored(self, rev):
        """Check if a file revision is censored."""
        return self.flags(rev) & revlog.REVIDX_ISCENSORED

24255:4bfe9f2d9761

# Copyright 2005-2007 Matt Mackall <[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 error, mdiff, revlog
import re, struct

_mdre = re.compile('\1\n')
def parsemeta(text):
    """return (metadatadict, keylist, metadatasize)"""
    # text can be buffer, so we can't use .startswith or .index

            raise

    def iscensored(self, rev):
        """Check if a file revision is censored."""
        return self.flags(rev) & revlog.REVIDX_ISCENSORED

    def _peek_iscensored(self, baserev, delta, flush):
        """Quickly check if a delta produces a censored revision."""
        # Fragile heuristic: unless new file meta keys are added alphabetically
        # preceding "censored", all censored revisions are prefixed by
        # "\1\ncensored:". A delta producing such a censored revision must be a
        # full-replacement delta, so we inspect the first and only patch in the
        # delta for this prefix.
        hlen = struct.calcsize(">lll")
        if len(delta) <= hlen:
            return False

        oldlen = self.rawsize(baserev)
        newlen = len(delta) - hlen
        if delta[:hlen] != mdiff.replacediffheader(oldlen, newlen):
            return False

        add = "\1\ncensored:"
        addlen = len(add)
        return newlen >= addlen and delta[hlen:hlen + addlen] == add