I want to create custom resource pack with implement of IResourcePack, I saw I need to make 8 functions.

I'm migrating mod from 1.12.2 to 1.16.5, I have

class OutResource(root: String): IResourcePack {
    override fun getInputStream(location: ResourceLocation): InputStream {
        return FileInputStream(File(rootDir, location.path))
    }

    override fun resourceExists(location: ResourceLocation): Boolean {
        return File(rootDir, location.path).exists()
    }

    override fun getResourceDomains(): MutableSet<String> {
        return domains
    }

    override fun <T : IMetadataSection?> getPackMetadata(
        metadataSerializer: MetadataSerializer,
        metadataSectionName: String
    ): T? {
        return null
    }

    override fun getPackImage(): BufferedImage? {
        return null
    }

    override fun getPackName(): String {
        return name
    }

    val rootDir = File(name)
    companion object {
        val name = ImageOverlayMod.MOD_ID
        val domains = setOf(name).toMutableSet()
    }
}

But I have no idea how to implement getRootResourceStream, getResourceNamespaces, getMetadata.

What is meaning of those functions?

I'm making resource pack to get images from extend of jar file.

Thanks!