Deserialisation fails for objects after saving generic form in Tasklist

[ThorbenLindhauer]

This issue was imported from JIRA:

Field	Value
JIRA Link	CAM-13463
Reporter	@garima-camunda
Has restricted visibility comments	true

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What are the steps to reproduce your problem?

A sample application is attached for quick reference.

Steps followed

• Installed Camunda spring boot starter 7.15.0-ee
• Created Java Delegate with the name SomeDelegate which sets an object variable in Java API.
• Deployed sample BPMN <^recreate_error.bpmn> which calls this Java delegate via process application
• Started the server
• Go to tasklist, and start the process instance
• Now in Tasklist, go to the User Task, claim the task and "Load the variable" in generic User Task form
• Submit the generic user task form
• An exception is thrown as shown in the screenshot below  Stack trace shows following as cause:

  
  Caused by: com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot construct instance of `test.camunda.DeliveryInformation` (although at least one Creator exists): no String-argument constructor/factory method to deserialize from String value ('{"id":"f8d791db-924e-4def-a63a-da069298b26d","packages":<{"id":"id1","storageAreaId":"areaa1","storageId":"storage1","article":null}>,"carrier":"carrier1"}')
  at <Source: UNKNOWN; line: -1, column: -1>
  at com.fasterxml.jackson.databind.exc.MismatchedInputException.from(MismatchedInputException.java:63) <sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.DeserializationContext.reportInputMismatch(DeserializationContext.java:1455) </sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1081) <sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.deser.ValueInstantiator._createFromStringFallbacks(ValueInstantiator.java:371) </sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.deser.std.StdValueInstantiator.createFromString(StdValueInstantiator.java:323) <sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromString(BeanDeserializerBase.java:1408) </sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeOther(BeanDeserializer.java:176) <sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:166) </sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.ObjectMapper._readValue(ObjectMapper.java:4497) <sub><jackson-databind-2.11.3.jar:2.11.3>
  at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2799) </sub><jackson-databind-2.11.3.jar:2.11.3>
  at org.camunda.spin.impl.json.jackson.format.JacksonJsonDataFormatMapper.mapInternalToJava(JacksonJsonDataFormatMapper.java:98) ~<camunda-spin-dataformat-json-jackson-1.10.1.jar:1.10.1>
  ... 248 common frames omitted

**What is the problem?**  
Deserialization fails for object

**What would be the expected behavior:** 
No error in saving serialized object

**Hints (optional):**

* This always happens when you submit an object variable from the task form (you can also create a new one and look up the variable in the history, it cannot be deserialized as well). 
* The quotation marks used in the serialized String are not handled correctly. This works all fine in the "Add Variable to Process Instance" dialog in Cockpit

**Links:**
* is related to https://jira.camunda.com/browse/SUPPORT-10620

[ThorbenLindhauer]

This comment was imported from JIRA and written by user akPKWEz

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This bug makes using the generic task form and using objects in process variables mutually exclusive. Since its mostly about removing one level of escaping, it would be great if this can be fixed soon

[nikku]

I heard rumors that @derari is interested in fixing this issue.

Is there any advice we can give a community contributor on where to dig? I guess it is the core engine, not tasklist failing here?

[ThorbenLindhauer]

Hi Nico,

This needs a fix in tasklist. Tasklist makes the following request:

POST http://localhost:8080/camunda/api/engine/engine/default/task/<task id>/submit-form

{
  "variables": {
    "myPojo": {
      "value": "\"{\\\"prop1\\\":\\\"foo\\\",\\\"prop2\\\":42}\"",
      "type": "Object",
      "valueInfo": {
        "objectTypeName": "org.camunda.bpm.platform.example.servlet.MyPojo",
        "serializationDataFormat": "application/json"
      }
    }
  }
}

whereas the correct request body would be:

{
  "variables": {
    "myPojo": {
      "value": "{\"prop1\":\"foo\",\"prop2\":42}",
      "type": "Object",
      "valueInfo": {
        "objectTypeName": "org.camunda.bpm.platform.example.servlet.MyPojo",
        "serializationDataFormat": "application/json"
      }
    }
  }
}

So a bit too much escaping going on. When fixing this, we should also check if that impacts any of the other variable types and make sure we are not introducing regressions.

Cheers, Thorben

edit: I don't have a pointer to the corresponding code as I'm not that familiar with the frontend code. But happy to let someone else look into this if there is a serious interest in contributing and another hint is needed :)