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diff mercurial/filelog.py @ 24255:4bfe9f2d9761

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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
author Mike Edgar <adgar@google.com>
date Wed, 14 Jan 2015 15:16:08 -0500
parents 903c7e8c97ad
children 34bd1a5eef5b
line wrap: on
line diff
--- a/mercurial/filelog.py	Fri Mar 06 22:43:47 2015 -0800
+++ b/mercurial/filelog.py	Wed Jan 14 15:16:08 2015 -0500
@@ -5,8 +5,8 @@
 # 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
+import error, mdiff, revlog
+import re, struct
 
 _mdre = re.compile('\1\n')
 def parsemeta(text):
@@ -107,3 +107,23 @@
     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