X-Git-Url: https://git.decadent.org.uk/gitweb/?a=blobdiff_plain;f=daklib%2Ffstransactions.py;fp=daklib%2Ffstransactions.py;h=8fb737674fecb30a9bb4d43e3d4433543399b857;hb=4d8b174b33c1816762251a27dc9325138c8d8f6b;hp=0000000000000000000000000000000000000000;hpb=04c332f3fa9936f457a4c78ec6f72ca7faea0a82;p=dak.git

diff --git a/daklib/fstransactions.py b/daklib/fstransactions.py
new file mode 100644
index 00000000..8fb73767
--- /dev/null
+++ b/daklib/fstransactions.py
@@ -0,0 +1,201 @@
+# Copyright (C) 2012, Ansgar Burchardt <ansgar@debian.org>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+"""Transactions for filesystem actions
+"""
+
+import errno
+import os
+import shutil
+
+class _FilesystemAction(object):
+    @property
+    def temporary_name(self):
+        raise NotImplementedError()
+
+    def check_for_temporary(self):
+        try:
+            if os.path.exists(self.temporary_name):
+                raise IOError("Temporary file '{0}' already exists.".format(self.temporary_name))
+        except NotImplementedError:
+            pass
+
+class _FilesystemCopyAction(_FilesystemAction):
+    def __init__(self, source, destination, link=True, symlink=False, mode=None):
+        self.destination = destination
+        self.need_cleanup = False
+
+        self.check_for_temporary()
+        destdir = os.path.dirname(self.destination)
+        if not os.path.exists(destdir):
+            os.makedirs(destdir, 0o2775)
+        if symlink:
+            os.symlink(source, self.destination)
+        elif link:
+            try:
+                os.link(source, self.destination)
+            except OSError:
+                shutil.copy2(source, self.destination)
+        else:
+            shutil.copy2(source, self.destination)
+
+        self.need_cleanup = True
+        if mode is not None:
+            os.chmod(self.destination, mode)
+
+    @property
+    def temporary_name(self):
+        return self.destination
+
+    def commit(self):
+        pass
+
+    def rollback(self):
+        if self.need_cleanup:
+            os.unlink(self.destination)
+            self.need_cleanup = False
+
+class _FilesystemUnlinkAction(_FilesystemAction):
+    def __init__(self, path):
+        self.path = path
+        self.need_cleanup = False
+
+        self.check_for_temporary()
+        os.rename(self.path, self.temporary_name)
+        self.need_cleanup = True
+
+    @property
+    def temporary_name(self):
+        return "{0}.dak-rm".format(self.path)
+
+    def commit(self):
+        if self.need_cleanup:
+            os.unlink(self.temporary_name)
+            self.need_cleanup = False
+
+    def rollback(self):
+        if self.need_cleanup:
+            os.rename(self.temporary_name, self.path)
+            self.need_cleanup = False
+
+class _FilesystemCreateAction(_FilesystemAction):
+    def __init__(self, path):
+        self.path = path
+        self.need_cleanup = True
+
+    @property
+    def temporary_name(self):
+        return self.path
+
+    def commit(self):
+        pass
+
+    def rollback(self):
+        if self.need_cleanup:
+            os.unlink(self.path)
+            self.need_cleanup = False
+
+class FilesystemTransaction(object):
+    """transactions for filesystem actions"""
+    def __init__(self):
+        self.actions = []
+
+    def copy(self, source, destination, link=True, symlink=False, mode=None):
+        """copy `source` to `destination`
+
+        Args:
+           source (str): source file
+           destination (str): destination file
+
+        Kwargs:
+           link (bool): Try hardlinking, falling back to copying.
+           symlink (bool): Create a symlink instead
+           mode (int): Permissions to change `destination` to.
+        """
+        self.actions.append(_FilesystemCopyAction(source, destination, link=link, symlink=symlink, mode=mode))
+
+    def move(self, source, destination, mode=None):
+        """move `source` to `destination`
+
+        Args:
+           source (str): source file
+           destination (str): destination file
+
+        Kwargs:
+           mode (int): Permissions to change `destination` to.
+        """
+        self.copy(source, destination, link=True, mode=mode)
+        self.unlink(source)
+
+    def unlink(self, path):
+        """unlink `path`
+
+        Args:
+           path (str): file to unlink
+        """
+        self.actions.append(_FilesystemUnlinkAction(path))
+
+    def create(self, path, mode=None):
+        """create `filename` and return file handle
+
+        Args:
+           filename (str): file to create
+
+        Kwargs:
+           mode (int): Permissions for the new file
+
+        Returns:
+           file handle of the new file
+        """
+        destdir = os.path.dirname(path)
+        if not os.path.exists(destdir):
+            os.makedirs(destdir, 0o2775)
+        if os.path.exists(path):
+            raise IOError("File '{0}' already exists.".format(path))
+        fh = open(path, 'w')
+        self.actions.append(_FilesystemCreateAction(path))
+        if mode is not None:
+            os.chmod(path, mode)
+        return fh
+
+    def commit(self):
+        """Commit all recorded actions."""
+        try:
+            for action in self.actions:
+                action.commit()
+        except:
+            self.rollback()
+            raise
+        finally:
+            self.actions = []
+
+    def rollback(self):
+        """Undo all recorded actions."""
+        try:
+            for action in self.actions:
+                action.rollback()
+        finally:
+            self.actions = []
+
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        if type is None:
+            self.commit()
+        else:
+            self.rollback()
+        return None