releasetools: Fix the bug in symlink deletion.

For file-based OTAs, symlinks in the source build but not in the target
build will be deleted. However, if a symlink is replaced by a regular
file in the target build, the file will be accidentally deleted when
applying (resuming) the same package again.

Verify the checksum of a symlink that will be unpacked or renamed to.
Delete the file only if it doesn't have the target checksum.

Bug: 23646151
Change-Id: Ie322abb6022b6fa812c6b36a3127872d9614fc3b

tools/releasetools/edify_generator.py

@@ -243,6 +243,15 @@ class EdifyGenerator(object):
     cmd = "delete(" + ",\0".join(['"%s"' % (i,) for i in file_list]) + ");"
     self.script.append(self.WordWrap(cmd))
 
+  def DeleteFilesIfNotMatching(self, file_list):
+    """Delete the file in file_list if not matching the checksum."""
+    if not file_list:
+      return
+    for name, sha1 in file_list:
+      cmd = ('sha1_check(read_file("{name}"), "{sha1}") || '
+             'delete("{name}");'.format(name=name, sha1=sha1))
+      self.script.append(self.WordWrap(cmd))
+
   def RenameFile(self, srcfile, tgtfile):
     """Moves a file from one location to another."""
     if self.info.get("update_rename_support", False):
@@ -254,7 +263,7 @@ class EdifyGenerator(object):
     """Prepend an action with an apply_patch_check in order to
        skip the action if the file exists.  Used when a patch
        is later renamed."""
-    cmd = ('sha1_check(read_file("%s"), %s) || ' % (tgtfile, tgtsha1))
+    cmd = ('sha1_check(read_file("%s"), %s) ||' % (tgtfile, tgtsha1))
     self.script.append(self.WordWrap(cmd))
 
   def ApplyPatch(self, srcfile, tgtfile, tgtsize, tgtsha1, *patchpairs):

tools/releasetools/ota_from_target_files.py

@@ -1394,11 +1394,36 @@ else
   # Delete all the symlinks in source that aren't in target.  This
   # needs to happen before verbatim files are unpacked, in case a
   # symlink in the source is replaced by a real file in the target.
-  to_delete = []
+
+  # If a symlink in the source will be replaced by a regular file, we cannot
+  # delete the symlink/file in case the package gets applied again. For such
+  # a symlink, we prepend a sha1_check() to detect if it has been updated.
+  # (Bug: 23646151)
+  replaced_symlinks = dict()
+  if system_diff:
+    for i in system_diff.verbatim_targets:
+      replaced_symlinks["/%s" % (i[0],)] = i[2]
+  if vendor_diff:
+    for i in vendor_diff.verbatim_targets:
+      replaced_symlinks["/%s" % (i[0],)] = i[2]
+
+  if system_diff:
+    for tf in system_diff.renames.values():
+      replaced_symlinks["/%s" % (tf.name,)] = tf.sha1
+  if vendor_diff:
+    for tf in vendor_diff.renames.values():
+      replaced_symlinks["/%s" % (tf.name,)] = tf.sha1
+
+  always_delete = []
+  may_delete = []
   for dest, link in source_symlinks:
     if link not in target_symlinks_d:
-      to_delete.append(link)
-  script.DeleteFiles(to_delete)
+      if link in replaced_symlinks:
+        may_delete.append((link, replaced_symlinks[link]))
+      else:
+        always_delete.append(link)
+  script.DeleteFiles(always_delete)
+  script.DeleteFilesIfNotMatching(may_delete)
 
   if system_diff.verbatim_targets:
     script.Print("Unpacking new system files...")