filelog: raise CensoredNodeError when hash checks fail with censor metadata
With this change, when a revlog revision hash does not match its content, and
the content is empty with a special metadata key, the integrity failure is
assumed to be intentionally caused to remove sensitive content from repository
history.
To allow different Mercurial functionality to handle this scenario differently
a more specific exception is raised than "ordinary" hash failures.
Alternatives to this approach include, but are not limited to:
- Calling a hook when hashes mismatch to allow arbitrary tombstone validation.
Cons: Irresponsibly easy to disable integrity checking altogether.
- Returning empty revision data eagerly instead of raising, masking the error.
Cons: Push/pull won't roundtrip the tombstone, so client repos are unusable.
- Doing nothing differently at this layer. Callers must do their own detection
of tombstoned data if they want to handle some hash checks and not others.
- Impacts dozens of callsites, many of which don't have the revision data
- Would probably be missing one or two callsites at any given time
- Currently we throw a RevlogError, as do 12 other places in revlog.py.
Callers would need to parse the exception message and/or ensure
RevlogError is not thrown from any other part of their call tree.
#!/usr/bin/env python
import errno, os, sys
for f in sys.argv[1:]:
try:
print f, '->', os.readlink(f)
except OSError, err:
if err.errno != errno.EINVAL:
raise
print f, 'not a symlink'
sys.exit(0)