Compare with DB when loading library cache (fixes #256)

src/library/library.cr

@@ -25,20 +25,22 @@ class Library
     begin
       Compress::Gzip::Reader.open path do |content|
         loaded = Library.from_yaml content
+        # We will have to do a full restart in these cases. Otherwise having
+        #   two instances of the library will cause some weirdness.
         if loaded.dir != Config.current.library_path
-          # We will have to do a full restart in this case. Otherwise having
-          #   two instances of the library will cause some weirdness.
           Logger.fatal "Cached library dir #{loaded.dir} does not match " \
                        "current library dir #{Config.current.library_path}. " \
                        "Deleting cache"
-          File.delete path
-          Logger.fatal "Invalid library cache deleted. Mango needs to " \
-                       "perform a full reset to recover from this. " \
-                       "Pleae restart Mango."
-          Logger.fatal "Exiting"
-          exit 1
+          delete_cache_and_exit path
+        end
+        if loaded.title_ids.size > 0 &&
+           Storage.default.count_titles == 0
+          Logger.fatal "The library cache is inconsistent with the DB. " \
+                       "Deleting cache"
+          delete_cache_and_exit path
         end
         @@default = loaded
+        Logger.debug "Library cache loaded"
       end
       Library.default.register_jobs
     rescue e

src/storage.cr

@@ -619,6 +619,20 @@ class Storage
     {token, expires}
   end
 
+  def count_titles : Int32
+    count = 0
+    MainFiber.run do
+      get_db do |db|
+        db.query "select count(*) from titles" do |rs|
+          rs.each do
+            count = rs.read Int32
+          end
+        end
+      end
+    end
+    count
+  end
+
   def close
     MainFiber.run do
       unless @db.nil?

src/util/util.cr

@@ -163,3 +163,12 @@ def sanitize_filename(str : String) : String
     .gsub(/[\177\000-\031\\:\*\?\"<>\|]/, "")
   sanitized.size > 0 ? sanitized : random_str
 end
+
+def delete_cache_and_exit(path : String)
+  File.delete path
+  Logger.fatal "Invalid library cache deleted. Mango needs to " \
+               "perform a full reset to recover from this. " \
+               "Pleae restart Mango. This is NOT a bug."
+  Logger.fatal "Exiting"
+  exit 1
+end