Obfuscating a Polymorphic JSON Contract: Why [JsonDerivedType] Survives Renaming and TypeNameHandling Does Not
Property-level renaming breaks are annoying but shallow: a key comes out wrong, you pin it with [JsonPropertyName] , done. Polymorphic serialization is a deeper hazard, because the thing that goes on the wire is not a property name — it is the identity of the type itself . Obfuscation exists to destroy that identity. So a polymorphic contract is exactly the place where "renaming broke…
Renaming does not impact System.Text.Json's [JsonDerivedType] serialization, whereas Newtonsoft's TypeNameHandling does. With System.Text.Json, the wire format remains unchanged even after type renaming. To obfuscate a type hierarchy without relying on a single name, use opaque, intentional discriminators chosen as a wire vocabulary, rather than deriving them from the identifier. This approach ensures that even after obfuscation, the wire format remains identical and can be deserialized without issue.
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