largefiles: write .hg/largefiles/ files atomically
Before, it was possible to create a
.hg/largefiles/hash
file with truncated content, i.e., content where
SHA-1(content) != hash
This breaks the fundamental invariant in largefiles that the file
content for files in .hg/largefiles hash to the filename.
Test how largefiles abort in case the disk runs full
$ cat > criple.py <<EOF
> import os, errno, shutil
> from mercurial import util
> #
> # this makes the original largefiles code abort:
> def copyfileobj(fsrc, fdst, length=16*1024):
> fdst.write(fsrc.read(4))
> raise IOError(errno.ENOSPC, os.strerror(errno.ENOSPC))
> shutil.copyfileobj = copyfileobj
> #
> # this makes the rewritten code abort:
> def filechunkiter(f, size=65536, limit=None):
> yield f.read(4)
> raise IOError(errno.ENOSPC, os.strerror(errno.ENOSPC))
> util.filechunkiter = filechunkiter
> EOF
$ echo "[extensions]" >> $HGRCPATH
$ echo "largefiles =" >> $HGRCPATH
$ hg init alice
$ cd alice
$ echo "this is a very big file" > big
$ hg add --large big
$ hg commit --config extensions.criple=$TESTTMP/criple.py -m big
abort: No space left on device
[255]
The largefile is not created in .hg/largefiles:
$ ls .hg/largefiles
dirstate
The user cache is not even created:
>>> import os; os.path.exists("$HOME/.cache/largefiles/")
False