I've got a strange issue that I can't seem to reso...

# ktor

[Lev Teytelman]

I've got a strange issue that I can't seem to resolve. I have some data classes that look as follows:

@Serializable
data class Tag(
    val name: String,
    @Serializable(with = TagStringSerializer::class)
    val parent: Tag? = null,
    val subTags: MutableSet<@Serializable(with = TagStringSerializer::class) Tag> = ConcurrentSet(),
    val files: MutableSet<@Serializable(with = SavedFileStringSerializer::class) SavedFile> = ConcurrentSet()
)

@Serializable
data class SavedFile(
    @Serializable(with = FileSerializer::class)
    val file: File,
    val tags: MutableSet<@Serializable(with = TagStringSerializer::class) Tag> = ConcurrentSet()
)

Of course, I don't want recursive Tags/SavedFiles in my serialization, as that would lead to infinite loops; I only serialize the names (all my custom serializers do is extract names).
When I use ApplicationCall#respond(savedFile), this works properly and sends {"file":"example","tags":["test"]}.
However, when I do ApplicationCall#respond(savedFile.tags), I receive an array of default-serialized tags instead of just the names, as if it's ignoring the annotation in the set: [{"name":"test","subTags":[],"files":["example"]}].
Even stranger, when I do just Json.encodeToString(savedFile.tags), it works just fine and gives me a properly-encoded array ["test"].
Of course, I could just create a function like respondJson and wrap a call to respondText(Json.encodeToString(, but this seems hacky and non-ideal.
I'm just very confused as to why the two functions are behaving differently and how I can fix the serialization done within ApplicationCall#respond.

[Aleksei Tirman [JB]]

Can you share a sample project to troubleshoot your problem?

[Lev Teytelman]

Yes, here is an example that experiences the issue.
https://github.com/gecko10000/KtorSerializationExample
(use ./gradlew run to run it)
Requesting /r1 returns the properly serialized object, but requesting /r1children returns the children with default serialization, despite them being in a set with a specific serialization set. Moreover, requesting /r1childrenjson returns the proper string array and not an array of objects.

[Lev Teytelman]

I'm not sure if I'm even doing these serialization annotations correctly - is there some sort of protocol for recursive references in serializable classes like this?

[Lev Teytelman]

As in, how would I specify when to send all the children as serialized in the default manner, vs serialized with the special serializer?

[Lev Teytelman]

Maybe I should just use Collection mapping functions whenever I'm not returning an object directly... but then why does Json.encodeToString work properly? I'm worried that I will build my application around one behavior and suddenly begin to encounter another.

[Lev Teytelman]

any idea @Aleksei Tirman [JB]?

[Aleksei Tirman [JB]]

Since Ktor uses the typeInfo method from the reflection package to pass a type info to the ContentNegotiation plugin, I guess it loses the information about the serializer.

[Aleksei Tirman [JB]]

You better file an issue because that’s may be a bug.