swarming: delete named cache symlinks before workdir

client/named_cache.py

 # Copyright 2016 The LUCI Authors. All rights reserved.
 # Use of this source code is governed under the Apache License, Version 2.0
 # that can be found in the LICENSE file.
 
 """This file implements Named Caches."""
 
 import contextlib
 import logging
 import optparse
 import os
@@ skipping 123 matching lines @@
     """Returns timestamp of last use of an item.
 
     Requires NamedCache to be open.
 
     Raises KeyError if cache is not found.
     """
     self._lock.assert_locked()
     assert isinstance(name, basestring), name
     return self._lru.get_timestamp(name)
 
+  @contextlib.contextmanager
   def create_symlinks(self, root, named_caches):
-    """Creates symlinks in |root| for specified named_caches.
+    """Creates symlinks in |root| for the specified named_caches.
 
     named_caches must be a list of (name, path) tuples.
 
     Requires NamedCache to be open.
 
     Raises Error if cannot create a symlink.
     """
     self._lock.assert_locked()
     for name, path in named_caches:
       logging.info('Named cache %r -> %r', name, path)
       try:
-        if os.path.isabs(path):
-          raise Error('named cache path must not be absolute')
-        if '..' in path.split(os.path.sep):
-          raise Error('named cache path must not contain ".."')
+        _validate_named_cache_path(path)
         symlink_path = os.path.abspath(os.path.join(root, path))
         file_path.ensure_tree(os.path.dirname(symlink_path))
         requested = self.request(name)
         logging.info('Symlink %r to %r', symlink_path, requested)
         fs.symlink(requested, symlink_path)
       except (OSError, Error) as ex:
         raise Error(
             'cannot create a symlink for cache named "%s" at "%s": %s' % (
               name, symlink_path, ex))
 
+  def delete_symlinks(self, root, named_caches):
+    """Deletes symlinks from |root| for the specified named_caches.
+
+    named_caches must be a list of (name, path) tuples.
+    """
+    for name, path in named_caches:
+      logging.info('Unlinking named cache "%s"', name)
+      try:
+        _validate_named_cache_path(path)
+        symlink_path = os.path.abspath(os.path.join(root, path))
+        fs.unlink(symlink_path)
+      except (OSError, Error) as ex:
+        raise Error(
+            'cannot unlink cache named "%s" at "%s": %s' % (
+              name, symlink_path, ex))
+
   def trim(self, min_free_space):
     """Purges cache.
 
     Removes cache directories that were not accessed for a long time
     until there is enough free space and the number of caches is sane.
 
     If min_free_space is None, disk free space is not checked.
 
     Requires NamedCache to be open.
     """
@@ skipping 74 matching lines @@
     parser.error('--named-cache is specified, but --named-cache-root is empty')
   for name, path in options.named_caches:
     if not CACHE_NAME_RE.match(name):
       parser.error(
           'cache name "%s" does not match %s' % (name, CACHE_NAME_RE.pattern))
     if not path:
       parser.error('cache path cannot be empty')
   if options.named_cache_root:
     return CacheManager(os.path.abspath(options.named_cache_root))
   return None
+
+
+def _validate_named_cache_path(path):
+  if os.path.isabs(path):
+    raise Error('named cache path must not be absolute')
+  if '..' in path.split(os.path.sep):
+    raise Error('named cache path must not contain ".."')