Uploaded image for project: 'Spigot'
  1. Spigot
  2. SPIGOT-6749

Library Loader does not isolate dependencies



    • Bug
    • Resolution: Fixed
    • Minor
    • None
    • None
    • CraftBukkit version 3246-Spigot-6c1c1b2-dc764e7 (MC: 1.17.1) (Implementing API version 1.17.1-R0.1-SNAPSHOT)
    • Yes


      Expected Behavior

      Plugins should not see each others' libraries from the "library loader" feature, except in the case of dependencies between plugins.

      Actual Behavior

      If and only if a class in a library has already been loaded, other plugins can see the loaded class even when they do not depend on the plugin providing the library. This is incorrect behavior.

      How to use the Reproducer

      Refer to https://github.com/A248/SpigotLibraryLoaderReproducer

      1. Build with maven, "mvn package"
      2. Add the two plugins created by the reproducer build to the /plugins directory
      3. Start the server
      4. Observe log output


      This bug occurs because PluginClassLoader performs a "super.loadClass" call.


          Class<?> loadClass0(@NotNull String name, boolean resolve, boolean checkGlobal, boolean checkLibraries) throws ClassNotFoundException {
              try {
                  return super.loadClass(name, resolve);
              } catch (ClassNotFoundException ex) {
          // remaining implementation omitted

      As specified in the documentation of ClassLoader, and which is confirmed by the implementation, ClassLoader#loadClass will find an existing loaded class before trying to find the class from a jar file. The logic of loadClass is as follows:

      1. If there is an existing Class instance defined to the ClassLoader, yield that Class.
      2. Otherwise, check the parent ClassLoader for the Class instance.
      3. Otherwise again, check the "findClass" method.

      Per the reproducer, when PluginUsingLL loads the Caffeine class, the Caffeine class becomes defined to the ClassLoader of PluginUsingLL. When PluginIndependent later tries to load the Caffeine class, it can now see the Caffeine class from PluginUsingLL.





            Unassigned Unassigned
            A248 Anand Beh
            0 Vote for this issue
            2 Start watching this issue