hgext/git/manifest.py

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.

from mercurial import (
    match as matchmod,
    pathutil,
    pycompat,
    util,
)
from mercurial.interfaces import (
    repository,
    util as interfaceutil,
)
from . import gitutil


pygit2 = gitutil.get_pygit2()


@interfaceutil.implementer(repository.imanifestdict)
class gittreemanifest:
    """Expose git trees (and optionally a builder's overlay) as a manifestdict.

    Very similar to mercurial.manifest.treemanifest.
    """

    def __init__(self, git_repo, root_tree, pending_changes):
        """Initializer.

        Args:
          git_repo: The git_repo we're walking (required to look up child
              trees).
          root_tree: The root Git tree object for this manifest.
          pending_changes: A dict in which pending changes will be
              tracked. The enclosing memgittreemanifestctx will use this to
              construct any required Tree objects in Git during it's
              `write()` method.
        """
        self._git_repo = git_repo
        self._tree = root_tree
        if pending_changes is None:
            pending_changes = {}
        # dict of path: Optional[Tuple(node, flags)]
        self._pending_changes = pending_changes

    def _resolve_entry(self, path):
        """Given a path, load its node and flags, or raise KeyError if missing.

        This takes into account any pending writes in the builder.
        """
        upath = pycompat.fsdecode(path)
        ent = None
        if path in self._pending_changes:
            val = self._pending_changes[path]
            if val is None:
                raise KeyError
            return val
        t = self._tree
        comps = upath.split('/')
        te = self._tree
        for comp in comps[:-1]:
            te = te[comp]
            t = self._git_repo[te.id]
        ent = t[comps[-1]]
        if ent.filemode == pygit2.GIT_FILEMODE_BLOB:
            flags = b''
        elif ent.filemode == pygit2.GIT_FILEMODE_BLOB_EXECUTABLE:
            flags = b'x'
        elif ent.filemode == pygit2.GIT_FILEMODE_LINK:
            flags = b'l'
        else:
            raise ValueError('unsupported mode %s' % oct(ent.filemode))
        return ent.id.raw, flags

    def __getitem__(self, path):
        return self._resolve_entry(path)[0]

    def find(self, path):
        return self._resolve_entry(path)

    def __len__(self):
        return len(list(self.walk(matchmod.always())))

    def __nonzero__(self):
        try:
            next(iter(self))
            return True
        except StopIteration:
            return False

    __bool__ = __nonzero__

    def __contains__(self, path):
        try:
            self._resolve_entry(path)
            return True
        except KeyError:
            return False

    def iterkeys(self):
        return self.walk(matchmod.always())

    def keys(self):
        return list(self.iterkeys())

    def __iter__(self):
        return self.iterkeys()

    def __setitem__(self, path, node):
        self._pending_changes[path] = node, self.flags(path)

    def __delitem__(self, path):
        # TODO: should probably KeyError for already-deleted  files?
        self._pending_changes[path] = None

    def filesnotin(self, other, match=None):
        if match is not None:
            match = matchmod.badmatch(match, lambda path, msg: None)
            sm2 = set(other.walk(match))
            return {f for f in self.walk(match) if f not in sm2}
        return {f for f in self if f not in other}

    @util.propertycache
    def _dirs(self):
        return pathutil.dirs(self)

    def hasdir(self, dir):
        return dir in self._dirs

    def diff(self, other, match=lambda x: True, clean=False):
        """Finds changes between the current manifest and m2.

        The result is returned as a dict with filename as key and
        values of the form ((n1,fl1),(n2,fl2)), where n1/n2 is the
        nodeid in the current/other manifest and fl1/fl2 is the flag
        in the current/other manifest. Where the file does not exist,
        the nodeid will be None and the flags will be the empty
        string.
        """
        result = {}

        def _iterativediff(t1, t2, subdir):
            """compares two trees and appends new tree nodes to examine to
            the stack"""
            if t1 is None:
                t1 = {}
            if t2 is None:
                t2 = {}

            for e1 in t1:
                realname = subdir + pycompat.fsencode(e1.name)

                if e1.type == pygit2.GIT_OBJ_TREE:
                    try:
                        e2 = t2[e1.name]
                        if e2.type != pygit2.GIT_OBJ_TREE:
                            e2 = None
                    except KeyError:
                        e2 = None

                    stack.append((realname + b'/', e1, e2))
                else:
                    n1, fl1 = self.find(realname)

                    try:
                        e2 = t2[e1.name]
                        n2, fl2 = other.find(realname)
                    except KeyError:
                        e2 = None
                        n2, fl2 = (None, b'')

                    if e2 is not None and e2.type == pygit2.GIT_OBJ_TREE:
                        stack.append((realname + b'/', None, e2))

                    if not match(realname):
                        continue

                    if n1 != n2 or fl1 != fl2:
                        result[realname] = ((n1, fl1), (n2, fl2))
                    elif clean:
                        result[realname] = None

            for e2 in t2:
                if e2.name in t1:
                    continue

                realname = subdir + pycompat.fsencode(e2.name)

                if e2.type == pygit2.GIT_OBJ_TREE:
                    stack.append((realname + b'/', None, e2))
                elif match(realname):
                    n2, fl2 = other.find(realname)
                    result[realname] = ((None, b''), (n2, fl2))

        stack = []
        _iterativediff(self._tree, other._tree, b'')
        while stack:
            subdir, t1, t2 = stack.pop()
            # stack is populated in the function call
            _iterativediff(t1, t2, subdir)

        return result

    def setflag(self, path, flag):
        node, unused_flag = self._resolve_entry(path)
        self._pending_changes[path] = node, flag

    def get(self, path, default=None):
        try:
            return self._resolve_entry(path)[0]
        except KeyError:
            return default

    def flags(self, path):
        try:
            return self._resolve_entry(path)[1]
        except KeyError:
            return b''

    def copy(self):
        return gittreemanifest(
            self._git_repo, self._tree, dict(self._pending_changes)
        )

    def items(self):
        for f in self:
            # TODO: build a proper iterator version of this
            yield self[f]

    def iteritems(self):
        return self.items()

    def iterentries(self):
        for f in self:
            # TODO: build a proper iterator version of this
            yield self._resolve_entry(f)

    def text(self):
        assert False  # TODO can this method move out of the manifest iface?

    def _walkonetree(self, tree, match, subdir):
        for te in tree:
            # TODO: can we prune dir walks with the matcher?
            realname = subdir + pycompat.fsencode(te.name)
            if te.type == pygit2.GIT_OBJ_TREE:
                for inner in self._walkonetree(
                    self._git_repo[te.id], match, realname + b'/'
                ):
                    yield inner
            elif match(realname):
                yield pycompat.fsencode(realname)

    def walk(self, match):
        # TODO: this is a very lazy way to merge in the pending
        # changes. There is absolutely room for optimization here by
        # being clever about walking over the sets...
        baseline = set(self._walkonetree(self._tree, match, b''))
        deleted = {p for p, v in self._pending_changes.items() if v is None}
        pend = {p for p in self._pending_changes if match(p)}
        return iter(sorted((baseline | pend) - deleted))


@interfaceutil.implementer(repository.imanifestrevisionstored)
class gittreemanifestctx:
    def __init__(self, repo, gittree):
        self._repo = repo
        self._tree = gittree

    def read(self):
        return gittreemanifest(self._repo, self._tree, None)

    def readfast(self, shallow=False):
        return self.read()

    def copy(self):
        # NB: it's important that we return a memgittreemanifestctx
        # because the caller expects a mutable manifest.
        return memgittreemanifestctx(self._repo, self._tree)

    def find(self, path):
        return self.read()[path]


@interfaceutil.implementer(repository.imanifestrevisionwritable)
class memgittreemanifestctx:
    def __init__(self, repo, tree):
        self._repo = repo
        self._tree = tree
        # dict of path: Optional[Tuple(node, flags)]
        self._pending_changes = {}

    def read(self):
        return gittreemanifest(self._repo, self._tree, self._pending_changes)

    def copy(self):
        # TODO: if we have a builder in play, what should happen here?
        # Maybe we can shuffle copy() into the immutable interface.
        return memgittreemanifestctx(self._repo, self._tree)

    def write(self, transaction, link, p1, p2, added, removed, match=None):
        # We're not (for now, anyway) going to audit filenames, so we
        # can ignore added and removed.

        # TODO what does this match argument get used for? hopefully
        # just narrow?
        assert not match or isinstance(match, matchmod.alwaysmatcher)

        touched_dirs = pathutil.dirs(list(self._pending_changes))
        trees = {
            b'': self._tree,
        }
        # path: treebuilder
        builders = {
            b'': self._repo.TreeBuilder(self._tree),
        }
        # get a TreeBuilder for every tree in the touched_dirs set
        for d in sorted(touched_dirs, key=lambda x: (len(x), x)):
            if d == b'':
                # loaded root tree above
                continue
            comps = d.split(b'/')
            full = b''
            for part in comps:
                parent = trees[full]
                try:
                    parent_tree_id = parent[pycompat.fsdecode(part)].id
                    new = self._repo[parent_tree_id]
                except KeyError:
                    # new directory
                    new = None
                full += b'/' + part
                if new is not None:
                    # existing directory
                    trees[full] = new
                    builders[full] = self._repo.TreeBuilder(new)
                else:
                    # new directory, use an empty dict to easily
                    # generate KeyError as any nested new dirs get
                    # created.
                    trees[full] = {}
                    builders[full] = self._repo.TreeBuilder()
        for f, info in self._pending_changes.items():
            if b'/' not in f:
                dirname = b''
                basename = f
            else:
                dirname, basename = f.rsplit(b'/', 1)
                dirname = b'/' + dirname
            if info is None:
                builders[dirname].remove(pycompat.fsdecode(basename))
            else:
                n, fl = info
                mode = {
                    b'': pygit2.GIT_FILEMODE_BLOB,
                    b'x': pygit2.GIT_FILEMODE_BLOB_EXECUTABLE,
                    b'l': pygit2.GIT_FILEMODE_LINK,
                }[fl]
                builders[dirname].insert(
                    pycompat.fsdecode(basename), gitutil.togitnode(n), mode
                )
        # This visits the buffered TreeBuilders in deepest-first
        # order, bubbling up the edits.
        for b in sorted(builders, key=len, reverse=True):
            if b == b'':
                break
            cb = builders[b]
            dn, bn = b.rsplit(b'/', 1)
            builders[dn].insert(
                pycompat.fsdecode(bn), cb.write(), pygit2.GIT_FILEMODE_TREE
            )
        return builders[b''].write().raw