Issue with deserialization when there are unexpected properties (due to null StreamReadConstraints)

[sbertault]

Hello,
We encountered a weird behaviour with jackson-core 2.15.0 that was not present in version 2.14.2 :
Disclaimer : this is a corner case (but still annoying ;))

When trying to unmarshall the raw json {"list":[{"type":"impl","unmappedKey":"unusedValue"}]}
with "type" being the discriminator for a sealed class, I get this error
com.fasterxml.jackson.databind.JsonMappingException: Cannot invoke "com.fasterxml.jackson.core.JsonParser.streamReadConstraints()" because "p" is null (through reference chain: com.orange.ccmd.connector.MyResponse["list"]->java.util.ArrayList[0])

In the debugger, there is no trace of a variable p being null though.
This happens only when there is all three conditions:

• an extra field in the json that is not mapped to a field of the target class
• an extra member in the class that is not present in the json.
• a class hierarchy

Here is a complete working unit test showing the bug, with the stacktrace :

import com.fasterxml.jackson.annotation.JsonProperty
import com.fasterxml.jackson.databind.DeserializationFeature
import com.fasterxml.jackson.databind.JsonMappingException
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.kotlin.KotlinModule
import io.kotest.assertions.throwables.shouldThrow
import io.kotest.matchers.shouldBe
import org.junit.jupiter.api.Test


internal class JacksonBugTest {

    private val objectMapper = ObjectMapper().apply {
        disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
        registerModules(KotlinModule.Builder().build())
    }

    @Test
    fun thisFails() {
        val rawResponse = """{"list":[{"type":"impl","unmappedKey":"unusedValue"}]}"""
        shouldThrow<JsonMappingException> {
            objectMapper.readValue(rawResponse, MyResponse::class.java)
        }
        /**
         * com.fasterxml.jackson.databind.JsonMappingException: Cannot invoke "com.fasterxml.jackson.core.JsonParser.streamReadConstraints()" because "p" is null (through reference chain: com.orange.ccmd.connector.MyResponse["list"]->java.util.ArrayList[0])
         * 	at app//com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:402)
         * 	at app//com.fasterxml.jackson.databind.JsonMappingException.wrapWithPath(JsonMappingException.java:373)
         * 	at app//com.fasterxml.jackson.databind.deser.std.CollectionDeserializer._deserializeFromArray(CollectionDeserializer.java:375)
         * 	at app//com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:244)
         * 	at app//com.fasterxml.jackson.databind.deser.std.CollectionDeserializer.deserialize(CollectionDeserializer.java:28)
         * 	at app//com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:545)
         * 	at app//com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:568)
         * 	at app//com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:439)
         * 	at app//com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1409)
         * 	at app//com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:352)
         * 	at app//com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185)
         * 	at app//com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:323)
         * 	at app//com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4825)
         * 	at app//com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3772)
         * 	at app//com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3740)
         * 	at app//com.orange.ccmd.connector.utils.CustomJacksonObjectMapperFactory.readObject(CustomJacksonJsonProvider.kt:36)
         */
    }

    @Test
    fun `is ok if no missing field in json`() {
        val rawResponse = """{"list":[{"type":"impl","missingInJson":"not missing","unmappedKey":"unusedValue"}]}"""
        val marshalled = objectMapper.readValue(rawResponse, MyResponse::class.java)
        marshalled shouldBe MyResponse(
            list = listOf(Base.Impl(
                type = "impl",
                missingInJson = "not missing"
            ))
        )
    }

    @Test
    fun `is ok if no extra field in json`() {
        val rawResponse = """{"list":[{"type":"impl"}]}"""
        val marshalled = objectMapper.readValue(rawResponse, MyResponse::class.java)
        marshalled shouldBe MyResponse(
            list = listOf(Base.Impl(
                type = "impl",
                missingInJson = null
            ))
        )
    }

    @Test
    fun `is ok if no class hierarchy`() {
        val rawResponse = """{"list":[{"type":"impl"}]}"""
        val marshalled = objectMapper.readValue(rawResponse, MyResponseWithoutHierarchy::class.java)
        marshalled shouldBe MyResponseWithoutHierarchy(
            list = listOf(Base.Impl(
                type = "impl",
                missingInJson = null
            ))
        )
    }
}

data class MyResponse(
    val list: List<Base>
)

data class MyResponseWithoutHierarchy(
    val list: List<Base.Impl>
)

sealed class Base  {
    companion object {
        @JsonCreator
        @JvmStatic
        fun unmarshall(
            @JsonProperty("missingInJson") missingInJson: String? = null,
            @JsonProperty("type") type: String? = null,
        ): Base? {
            return when (type) {
                "impl" -> Impl(
                    missingInJson = missingInJson,
                    type = type,
                )
                else -> null
            }
        }
    }

    data class Impl(
        val type: String? = null,
        val missingInJson: String? = null
    ) : Base()
}

Thanks for the invaluable work

[pjfanning]

this is best moved to https://github.com/FasterXML/jackson-module-kotlin/ - noone in the team that maintains the core Jackson modules uses Kotlin

[sbertault]

I detected it in a kotlin project but had the impression that I was in the core stack all the way. Will try to reproduce with java class hierarchy.

[sbertault]

Same behaviour in java. I am not even attaching the Kotlin module, nor am I using fancy java 17 stuff like records or sealed interface.

package jackson;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNull;

import java.util.List;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;

class JacksonBugTest {

    private ObjectMapper objectMapper() {
        ObjectMapper om = new ObjectMapper();
        om.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
        return om;
    }

    @Test
    void thisFails() {
        String rawResponse = "{\"list\":[{\"type\":\"impl\",\"unmappedKey\":\"unusedValue\"}]}";
        Assertions.assertThrows(JsonMappingException.class, () ->
                objectMapper().readValue(rawResponse, MyResponse.class));
    }

    @Test
    void isOkIfNoMissingFieldInJson() throws JsonProcessingException {
        String rawResponse = "{\"list\":[{\"type\":\"impl\",\"missingInJson\":\"not missing\",\"unmappedKey\":\"unusedValue\"}]}";
        MyResponse marshalled = objectMapper().readValue(rawResponse, MyResponse.class);
        assertEquals("impl", marshalled.getList().get(0).getType());
        assertEquals("not missing", marshalled.getList().get(0).getMissingInJson());
    }

    @Test
    void isOkIfNoExtraFieldInJson() throws JsonProcessingException {
        String rawResponse = "{\"list\":[{\"type\":\"impl\"}]}";
        MyResponse marshalled = objectMapper().readValue(rawResponse, MyResponse.class);
        assertEquals("impl", marshalled.getList().get(0).getType());
        assertNull(marshalled.getList().get(0).getMissingInJson());
    }

    @Test
    void isOkIfNoClassHierarchy() throws JsonProcessingException {
        String rawResponse = "{\"list\":[{\"type\":\"impl\"}]}";
        MyResponseWithoutHierarchy marshalled = objectMapper().readValue(rawResponse, MyResponseWithoutHierarchy.class);
        assertEquals("impl", marshalled.getList().get(0).getType());
        assertNull(marshalled.getList().get(0).getMissingInJson());
    }

}

class MyResponse {
    private List<Base> list;

    public List<Base> getList() {
        return list;
    }

    public void setList(List<Base> list) {
        this.list = list;
    }
}

class MyResponseWithoutHierarchy {

    private List<Impl> list;

    public List<Impl> getList() {
        return list;
    }

    public void setList(List<Impl> list) {
        this.list = list;
    }
}

interface Base {

    String getType();

    String getMissingInJson();

    @JsonCreator
    static Base unmarshall(
            @JsonProperty("missingInJson") String missingInJson,
            @JsonProperty("type") String type
    ) {
        return switch (type) {
            case "impl" -> new Impl(type, missingInJson);
            default -> null;
        };
    }
}

final class Impl implements Base {
    private String type;
    private String missingInJson;

    public Impl() {
    }

    public Impl(String type, String missingInJson) {
        this.type = type;
        this.missingInJson = missingInJson;
    }

    @Override public String getType() {
        return type;
    }

    @Override public String getMissingInJson() {
        return missingInJson;
    }

    public void setType(String type) {
        this.type = type;
    }

    public void setMissingInJson(String missingInJson) {
        this.missingInJson = missingInJson;
    }
}

[pjfanning]

@cowtowncoder can you move this to jackson-databind? I have a PR there - #3911

@sbertault thanks for the Java test case