view tests/test-fix-pickle.t @ 49269:395f28064826

worker: avoid potential partial write of pickled data

Previously, the code wrote the pickled data using os.write(). However,
os.write() can write less bytes than passed to it. To trigger the problem, the
pickled data had to be larger than 2147479552 bytes on my system.

Instead, open a file object and pass it to pickle.dump(). This also has the
advantage that it doesn’t buffer the whole pickled data in memory.

Note that the opened file must be buffered because pickle doesn’t support
unbuffered streams because unbuffered streams’ write() method might write less
bytes than passed to it (like os.write()) but pickle.dump() relies on that all
bytes are written (see https://github.com/python/cpython/issues/93050).

The side effect of using a file object and a with statement is that wfd is
explicitly closed now while it seems like before it was implicitly closed by
process exit.

A script that implements uppercasing all letters in a file.

  $ UPPERCASEPY="$TESTTMP/uppercase.py"
  $ cat > $UPPERCASEPY <<EOF
  > import sys
  > from mercurial.utils.procutil import setbinary
  > setbinary(sys.stdin)
  > setbinary(sys.stdout)
  > sys.stdout.write(sys.stdin.read().upper())
  > EOF
  $ TESTLINES="foo\nbar\nbaz\n"
  $ printf $TESTLINES | "$PYTHON" $UPPERCASEPY
  FOO
  BAR
  BAZ

This file attempts to test our workarounds for pickle's lack of
support for short reads.

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > fix =
  > [fix]
  > uppercase-whole-file:command="$PYTHON" $UPPERCASEPY
  > uppercase-whole-file:pattern=set:**
  > EOF

  $ hg init repo
  $ cd repo

# Create a file that's large enough that it seems to not fit in
# pickle's buffer, making it use the code path that expects our
# _blockingreader's read() method to return bytes.
  $ echo "some stuff" > file
  $ for i in $($TESTDIR/seq.py 13); do
  >   cat file file > tmp
  >   mv -f tmp file
  > done
  $ hg commit -Am "add large file"
  adding file

Check that we don't get a crash

  $ hg fix -r .
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/*-fix.hg (glob)