Delegating creator fails to work for binary data (byte[]) with binary formats (CBOR, Smile)

[ghost]

Jackson Versions: 2.8.9, 2.9.0.pr4

This issue might belong to jackson-dataformats-binary.

I created a class which is basically a wrapper around a byte[], using @JsonValue and @JsonCreator.
This works fine using the default JsonFactory, however when using a SimleFactory or CBORFactory (and probably others) the deserialization fails: It returns a byte[] instead of the expected target class (which causes a ClassCastException in the calling code).

This problem only occurs with byte[]. Other types such as int[], String[] or byte[][] are fine.

public class TestByteArray {
    private static class ByteArray {
        private final byte[] val;

        @JsonCreator public ByteArray(byte[] val) { this.val = val;}

        @JsonValue public byte[] getValue() { return val;}
    }

    public static void main(String[] args) throws IOException {
        //This works fine
        test(new ObjectMapper(new JsonFactory()));
        //This throws java.lang.ClassCastException: [B cannot be cast to TestByteArray$ByteArray
        test(new ObjectMapper(new SmileFactory()));
        System.out.println("No exception thrown.");
    }

    private static void test(ObjectMapper mapper) throws IOException {
        byte[] bytes = {1, 2, 3, 4, 5};
        ByteArray read = mapper.readValue(mapper.writeValueAsBytes(new ByteArray(bytes)), ByteArray.class);
        if (!Arrays.equals(bytes, read.val))
            throw new IllegalStateException("Arrays not equal");
    }
}

[cowtowncoder]

Thank you for reporting this. It could be either due to binary codecs, or databind not handling the case for some reason -- the way binary codecs expose binary content does differ from that of textual ones: whereas JSON parser has no way of knowing that a JSON String encodes byte[] (it must come from POJO type declaration), Smile/CBOR codecs do recognize it as binary and return JsonToken.VALUE_EMBEDDED_OBJECT. But why this prevents correct functioning of delegating creator is different story.

[cowtowncoder]

Yes, I can reproduce this as shown.

[cowtowncoder]

Interesting. Turns out that delegating-creator case was not covered for JsonToken.VALUE_EMBEDDED_OBJECT; I added this, fix will be in 2.8.10 / 2.9.0.
I think I will also add an explicit check to give better exception message in other cases; ability to "coerce" native/embedded object into target type is a powerful feature, but it has to obey JVM type limitations... so in this case it'd be better to get a JsonMappingException, instead of relying on JVM giving opaque ClassCastException with no context.