view tests/test-narrow-clone-non-narrow-server.t @ 46607:e9901d01d135

revlog: add a mechanism to verify expected file position before appending

If someone uses `hg debuglocks`, or some non-hg process writes to the .hg
directory without respecting the locks, or if the repo's on a networked
filesystem, it's possible for the revlog code to write out corrupted data.

The form of this corruption can vary depending on what data was written and how
that happened. We are in the "networked filesystem" case (though I've had users
also do this to themselves with the "`hg debuglocks`" scenario), and most often
see this with the changelog. What ends up happening is we produce two items
(let's call them rev1 and rev2) in the .i file that have the same linkrev,
baserev, and offset into the .d file, while the data in the .d file is appended
properly. rev2's compressed_size is accurate for rev2, but when we go to
decompress the data in the .d file, we use the offset that's recorded in the
index file, which is the same as rev1, and attempt to decompress
rev2.compressed_size bytes of rev1's data. This usually does not succeed. :)

When using inline data, this also fails, though I haven't investigated why too
closely. This shows up as a "patch decode" error. I believe what's happening
there is that we're basically ignoring the offset field, getting the data
properly, but since baserev != rev, it thinks this is a delta based on rev
(instead of a full text) and can't actually apply it as such.

For now, I'm going to make this an optional component and default it to entirely
off. I may increase the default severity of this in the future, once I've
enabled it for my users and we gain more experience with it. Luckily, most of my
users have a versioned filesystem and can roll back to before the corruption has
been written, it's just a hassle to do so and not everyone knows how (so it's a
support burden). Users on other filesystems will not have that luxury, and this
can cause them to have a corrupted repository that they are unlikely to know how
to resolve, and they'll see this as a data-loss event. Refusing to create the
corruption is a much better user experience.

This mechanism is not perfect. There may be false-negatives (racy writes that
are not detected). There should not be any false-positives (non-racy writes that
are detected as such). This is not a mechanism that makes putting a repo on a
networked filesystem "safe" or "supported", just *less* likely to cause
corruption.

Differential Revision: https://phab.mercurial-scm.org/D9952

Test attempting a narrow clone against a server that doesn't support narrowhg.

  $ . "$TESTDIR/narrow-library.sh"

  $ hg init master
  $ cd master

  $ for x in `$TESTDIR/seq.py 10`; do
  >   echo $x > "f$x"
  >   hg add "f$x"
  >   hg commit -m "Add $x"
  > done

  $ hg serve -a localhost -p $HGPORT1 --config extensions.narrow=! -d \
  >    --pid-file=hg.pid
  $ cat hg.pid >> "$DAEMON_PIDS"
  $ hg serve -a localhost -p $HGPORT2 -d --pid-file=hg.pid
  $ cat hg.pid >> "$DAEMON_PIDS"

Verify that narrow is advertised in the bundle2 capabilities:

  $ cat >> unquote.py <<EOF
  > from __future__ import print_function
  > import sys
  > if sys.version[0] == '3':
  >     import urllib.parse as up
  >     unquote = up.unquote_plus
  > else:
  >     import urllib
  >     unquote = urllib.unquote_plus
  > print(unquote(list(sys.stdin)[1]))
  > EOF
  $ echo hello | hg -R . serve --stdio | \
  >   "$PYTHON" unquote.py | tr ' ' '\n' | grep narrow
  exp-narrow-1

  $ cd ..

  $ hg clone --narrow --include f1 http://localhost:$HGPORT1/ narrowclone
  requesting all changes
  abort: server does not support narrow clones
  [255]

Make a narrow clone (via HGPORT2), then try to narrow and widen
into it (from HGPORT1) to prove that narrowing is fine and widening fails
gracefully:
  $ hg clone -r 0 --narrow --include f1 http://localhost:$HGPORT2/ narrowclone
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files
  new changesets * (glob)
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd narrowclone
  $ hg tracked --addexclude f2 http://localhost:$HGPORT1/
  comparing with http://localhost:$HGPORT1/
  searching for changes
  looking for local changes to affected paths

  $ hg tracked --addinclude f1 http://localhost:$HGPORT1/
  nothing to widen or narrow

  $ hg tracked --addinclude f9 http://localhost:$HGPORT1/
  comparing with http://localhost:$HGPORT1/
  abort: server does not support narrow clones
  [255]