I m currently working with the nextcloud api and have some p

Question

I m currently working with the nextcloud api and have some problems deserializing it For example I get the following answer stripped all unneeded stuff So the problem is that I get the `ocs data groups` property as `Map lt String Long gt ` if there are some groups and permissions The long available or as empty Array if nothing is set there This problem I also have on the `ocs data` level on some other api endpoints Kotlin 1 8 20 kotlinx serialization Plugin 1 8 20 kotlinx serialization 1 5 0 ``` ocs meta data 1 groups 2 groups admin 7 ``` I tried implementing a `TransformEmptyArrayAsObjectSerializer` like so ```internal open class TransformEmptyArrayAsObjectSerializer lt T Any gt tSerializer KSerializer lt T gt JsonTransformingSerializer lt T gt tSerializer override fun transformDeserialize element JsonElement JsonElement = if element is JsonArray buildJsonObject else element ``` But after annotating the object with ` Serializable with = TransformEmptyArrayAsObjectSerializer class ` there is a weird compiler error and IntelliJ is highlighting the line with `Class TransformEmptyArrayAsObjectSerializer lt gt which is serializer for type Any is applied here to type Map lt String Set lt PermissionType gt gt This may lead to errors or incorrect behavior` Which I do not undestand correctly but I think it s about type erasure The data class definitions and the weird compile message can be found in the thread Question How can this be solved

maxemann96 · Answer

``` Serializable internal data class Ocs lt T Any gt val ocs OcsEntity lt T gt Serializable internal data class OcsEntity lt T Any gt val meta MetaEntity Serializable with = TransformEmptyArrayAsObjectSerializer class val data T Serializable internal data class MetaEntity SerialName status val status String SerialName statuscode val statusCode Int SerialName message val message String Serializable public data class GroupFolderDetails SerialName id val id Int SerialName mount point val mountPoint String empty array or a map of groups with their permissions SerialName groups Serializable with = TransformEmptyArrayAsObjectSerializer class val groups Map lt String Set lt PermissionType gt gt = null SerialName quota val quota Long SerialName size val size Long needs 64 bit integer SerialName acl val acl Boolean SerialName manage val manage List lt GroupFolderManageDetails gt = null ``` Tried to deserialize it as `Ocs lt Map lt String GroupFolderDetails gt gt `

maxemann96 · Answer

```e org jetbrains kotlin backend common BackendException Backend Internal error Exception during IR lowering File being compiled home maximilian Development iog feather nextcloud src main kotlin dev maximilian feather nextcloud groupfolders entities GroupFolderDetails kt The root cause java lang RuntimeException was thrown at org jetbrains kotlin backend jvm codegen FunctionCodegen generate FunctionCodegen kt 51 Caused by java lang RuntimeException Exception while generating code for FUN CLASS STATIC INITIALIZER name lt clinit gt visibility public package modality FINAL lt gt returnType kotlin Unit BLOCK BODY SET FIELD FIELD FIELD FOR OBJECT INSTANCE name Companion type dev maximilian feather nextcloud groupfolders entities GroupFolderDetails Companion visibility public final static type=kotlin Unit origin=INITIALIZE FIELD value CONSTRUCTOR CALL public constructor lt init gt $constructor marker kotlin jvm internal DefaultConstructorMarker declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails Companion type=dev maximilian feather nextcloud groupfolders entities GroupFolderDetails Companion origin=null $constructor marker CONST Null type=kotlin jvm internal DefaultConstructorMarker value=null BLOCK type=kotlin Unit origin=SYNTHESIZED INIT BLOCK SET FIELD FIELD COMPANION PROPERTY BACKING FIELD name $childSerializers type kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt visibility private final static type=kotlin Unit origin=null value BLOCK type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null VAR IR TEMPORARY VARIABLE name tmp0 type kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val CALL public final fun arrayOfNulls lt T gt size kotlin Array lt T of kotlin arrayOfNulls gt declared in kotlin type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null lt T gt kotlinx serialization KSerializer lt kotlin Any gt size CONST Int type= value=7 CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=0 value CONST Null type=kotlin Nothing value=null CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=1 value CONST Null type=kotlin Nothing value=null CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=2 value CONSTRUCTOR CALL public constructor lt init gt tSerializer kotlinx serialization KSerializer lt T of dev maximilian feather nextcloud TransformEmptyArrayAsObjectSerializer gt primary declared in dev maximilian feather nextcloud TransformEmptyArrayAsObjectSerializer type=dev maximilian feather nextcloud TransformEmptyArrayAsObjectSerializer lt kotlin String gt origin=null lt class T gt lt none gt CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=3 value CONST Null type=kotlin Nothing value=null CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=4 value CONST Null type=kotlin Nothing value=null CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=5 value CONST Null type=kotlin Nothing value=null CALL public final fun set index value T of kotlin Array kotlin Unit operator declared in kotlin Array type=kotlin Unit origin=null $this GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null index CONST Int type= value=6 value CONSTRUCTOR CALL public constructor lt init gt element kotlinx serialization KSerializer lt E of kotlinx serialization internal ArrayListSerializer gt primary declared in kotlinx serialization internal ArrayListSerializer type=kotlinx serialization internal ArrayListSerializer lt dev maximilian feather nextcloud groupfolders entities GroupFolderManageDetails gt origin=null lt class E gt lt none gt element GET FIELD FIELD FIELD FOR OBJECT INSTANCE name INSTANCE type dev maximilian feather nextcloud groupfolders entities GroupFolderManageDetails $serializer visibility public final static type=dev maximilian feather nextcloud groupfolders entities GroupFolderManageDetails $serializer origin=null GET VAR val tmp0 kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt val declared in dev maximilian feather nextcloud groupfolders entities GroupFolderDetails lt clinit gt type=kotlin Array lt kotlinx serialization KSerializer lt kotlin Any gt gt origin=null at org jetbrains kotlin backend jvm codegen FunctionCodegen generate FunctionCodegen kt 51 ```

Adam S · Answer

in the example JSON you gave `ocs data` is always an object but in the `OcsEntity` class you ve set the `data` property to use your custom serializer that doesn t seem right to me

maxemann96 · Answer

This case also happens always an object or an empty array for `ocs data` or `ocs data groups` ``` ocs meta data ```

Adam S · Answer

if you want to get something going quickly you could just use `val data JsonObject` and then manually transform the data Okay sure it s nice to use a serializer and hide away the JSON logic but sometimes it s easier to decode it with Kotlin code

Adam S · Answer

ah okay gotcha Hmm

maxemann96 · Answer

Setting the `groups` attribute from the `GroupFolderDetails` a specific inherited serializer works But this does not work on the `ocs data` level ```internal object GroupFolderGroupDetailsSerializer TransformEmptyArrayAsObjectSerializer lt Map lt String Set lt PermissionType gt gt gt MapSerializer String serializer PermissionTypeSetSerializer Serializable public data class GroupFolderDetails SerialName groups Serializable with = GroupFolderGroupDetailsSerializer class val groups Map lt String Set lt PermissionType gt gt = null ```

maxemann96 · Answer

Also found a workaround for the other case ```internal object GroupFoldersAnswerEntitySerializer TransformEmptyArrayAsObjectSerializer lt Map lt String GroupFolderDetails gt gt MapSerializer String serializer GroupFolderDetails serializer Serializable with = GroupFoldersAnswerEntitySerializer class internal sealed interface GroupFoldersAnswerEntity Map lt String GroupFolderDetails gt ``` and then deserializing it as `Ocs lt GroupFoldersAnswerEntity gt ` But I would love to get a workaround that is not that specific and generically useable

Adam S · Answer

I had to handle a similar problem where an empty array would be encoded to an empty JSON object I solved it by using a value class with a custom serializer and using that `MyValueClass lt T gt ` instead of `List lt T gt ` I ll se if I can come up with an example that works for your case

Adam S · Answer

try this I defined a value class `NextCloudData lt T gt ` that has a custom serializer `NextCloudDataSerializer lt T Any gt ` Value classes are nice in KxS because they can be equivalent to an existing type in this instance a `Map lt String T gt ` but you can attach specific serialization logic to them Instead of using the JSON Transform serializer I like implementing a KSerializer because it gives a little more control over the logic If `NextCloudDataSerializer` is decoding JSON then it can first decode to the polymorphic `JsonElement` type and if it matches your requirements then it will use a delegate serializer of type `Map lt String T gt ` to decode the value properly In code you can use `NextCloudData lt T gt ` in any place where you would normally use a `Map lt String T gt `

maxemann96 · Answer

My time ran out today I will look into this later Thank you for the ideas

maxemann96 · Answer

This case also is possible ``` ocs meta data success true ``` Which correctly gets deserialized with ``` Serializable internal data class SuccessResponse val success Boolean ``` as `Ocs lt SuccessResponse gt ` So only if I expect a `Map lt String T gt ` then there is this weird behavior of ` ` or a normal encoded Map as json object Possibly there are some other weird nextcloud edge cases but I currently discovered them not until yet

ephemient · Answer

I don t understand why they would do that

ephemient · Answer

I ve seen APIs that return ` ` for empty which is equally annoying to deal with in a strictly typed language but kinda makes some sense in JS `Boolean null == Boolean == false` `Boolean == Boolean == true`

ephemient · Answer

in any case if that s something they always do I think it would be better to handle it in the format rather than in individual serializers

ephemient · Answer

unfortunately it s not really something easily customized in kotlinx serialization now

ephemient · Answer

but I have made a few things like <https kotlinlang slack com archives C7A1U5PTM p1653151131184099 thread ts=1653099160 150059 amp cid=C7A1U5PTM> which show that it s possible with effort