view tests/test-issue1802.t @ 26375:3686fa2b8eee

windows: insert file positioning call between reads and writes

fopen() and fdopen() have a unique-to-Windows requirement that
transitions between read and write operations in files opened
in modes r+, w+, and a+ perform a file positioning call
(fsetpos, fseek, or rewind) in between. While the MSDN docs don't
say what will happen if this is not done, observations reveal
that Python raises an IOError with errno 0. Furthermore, I
/think/ this behavior isn't deterministic. But I can reproduce
it reliably with subsequent patches applied that open revlogs
in a+ mode and perform both reads and writes.

This patch introduces a proxy class for file handles opened
in r+, w+, and a+ mode on Windows. The class intercepts calls
and audits whether a file positioning function has been called
between read and write operations. If not, a dummy, no-op seek
to the current file position is performed. This appears to be
sufficient to "trick" Windows into allowing transitions between
read and writes without raising errors.

#require execbit

Create extension that can disable exec checks:

  $ cat > noexec.py <<EOF
  > from mercurial import extensions, util
  > def setflags(orig, f, l, x):
  >     pass
  > def checkexec(orig, path):
  >     return False
  > def extsetup(ui):
  >     extensions.wrapfunction(util, 'setflags', setflags)
  >     extensions.wrapfunction(util, 'checkexec', checkexec)
  > EOF

  $ hg init unix-repo
  $ cd unix-repo
  $ touch a
  $ hg add a
  $ hg commit -m 'unix: add a'
  $ hg clone . ../win-repo
  updating to branch default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ chmod +x a
  $ hg commit -m 'unix: chmod a'
  $ hg manifest -v
  755 * a

  $ cd ../win-repo

  $ touch b
  $ hg add b
  $ hg commit -m 'win: add b'

  $ hg manifest -v
  644   a
  644   b

  $ hg pull
  pulling from $TESTTMP/unix-repo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 0 changes to 0 files (+1 heads)
  (run 'hg heads' to see heads, 'hg merge' to merge)

  $ hg manifest -v -r tip
  755 * a

Simulate a Windows merge:

  $ hg --config extensions.n=$TESTTMP/noexec.py merge --debug
    searching for copies back to rev 1
    unmatched files in local:
     b
  resolving manifests
   branchmerge: True, force: False, partial: False
   ancestor: a03b0deabf2b, local: d6fa54f68ae1+, remote: 2d8bcf2dda39
   a: update permissions -> e
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

Simulate a Windows commit:

  $ hg --config extensions.n=$TESTTMP/noexec.py commit -m 'win: merge'

  $ hg manifest -v
  755 * a
  644   b

  $ cd ..