[HDDS-8551] Fix the generic type of CodecRegistry.getCodec

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.4.0
• Component/s: db
• Labels: pull-request-available
• Assignee: Tsz-wo Sze
• Reporter: Tsz-wo Sze
• Created: 05/May/23 15:40
• Updated: 08/May/23 11:32
• Resolved: 08/May/23 11:32

Description

//CodecRegistry.java
  private <T> Codec<T> getCodec(Class<T> format) {
    final List<Class<?>> classes = new ArrayList<>();
    classes.add(format);
    classes.addAll(ClassUtils.getAllSuperclasses(format));
    classes.addAll(ClassUtils.getAllInterfaces(format));
    for (Class<?> clazz : classes) {
      final Codec<?> codec = valueCodecs.get(clazz);
      if (codec != null) {
        return (Codec<T>) codec;
      }
    }
    throw new IllegalStateException(
        "Codec is not registered for type: " + format);
  }

In the code above, it tries to get a codec from the super classes and interfaces of T.

Suppose Class<T> is not in valueCodecs and Class<S> is in valueCodecs, where S is a super class/interface of T and S != T. The method will return Codec<S>. However, Codec<S> is a lossy codec:

• Codec<S> can serialize T as S, possibly losing the extra information in T but not in S;
• Codec<S> cannot deserialize T – it will return S instead.

In such cases, the returned Codec<S> does not match the return type Codec<T>.

Issue Links

• links to: GitHub Pull Request #4667