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

.

Can you share a sample project to troubleshoot your problem?

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.

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.