JsonConverter type of: UnixDateTimeConverter throws exception

[FunkeeDan]

C# Destination types

[JsonConverter(typeof(UnixDateTimeConverter))]
public DateTime startdate;
[JsonConverter(typeof(UnixDateTimeConverter))]
public DateTime enddate;

Source JSON

{"data":[{"startdate":1568067791,"enddate":1577836800}],"state":""}

Expected behavior

The Json.NET package should deserialise the unix timestamp in the json data to System.DateTime instead of as an integer/string/other. This value deserialises correctly in Editor.

Actual behavior

When running an iOS build on iPhone this code throws exceptions:

JsonException: No parameterless constructor defined for 'Newtonsoft.Json.Converters.UnixDateTimeConverter'.
 at Newtonsoft.Json.Serialization.JsonTypeReflector+<>c__DisplayClass22_0.<GetCreator>b__0 (System.Object[] parameters) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonTypeReflector.GetJsonConverter (System.Object attributeProvider) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.SetPropertySettingsFromAttributes (Newtonsoft.Json.Serialization.JsonProperty property, System.Object attributeProvider, System.String name, System.Type declaringType, Newtonsoft.Json.MemberSerialization memberSerialization, System.Boolean& allowNonPublicAccess) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateProperty (System.Reflection.MemberInfo member, Newtonsoft.Json.MemberSerialization memberSerialization) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateProperties (System.Type type, Newtonsoft.Json.MemberSerialization memberSerialization) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateObjectContract (System.Type objectType) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract (System.Type objectType) [0x00000] in <00000000000000000000000000000000>:0 
 at System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue].GetOrAdd (TKey key, System.Func`2[T,TResult] valueFactory) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateList (System.Collections.IList list, Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonArrayContract contract, Newtonsoft.Json.Serialization.JsonProperty containerProperty, System.String id) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateList (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, System.Object existingValue, System.String id) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue (Newtonsoft.Json.Serialization.JsonProperty property, Newtonsoft.Json.JsonConverter propertyConverter, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerProperty, Newtonsoft.Json.JsonReader reader, System.Object target) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject (System.Object newObject, Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonObjectContract contract, Newtonsoft.Json.Serialization.JsonProperty member, System.String id) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize (Newtonsoft.Json.JsonReader reader, System.Type objectType, System.Boolean checkAdditionalContent) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.JsonSerializer.DeserializeInternal (Newtonsoft.Json.JsonReader reader, System.Type objectType) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.JsonConvert.DeserializeObject (System.String value, System.Type type, Newtonsoft.Json.JsonSerializerSettings settings) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.JsonConvert.DeserializeObject[T] (System.String value, Newtonsoft.Json.JsonSerializerSettings settings) [0x00000] in <00000000000000000000000000000000>:0 
 at ProductGenius.Utilities.ServerFunctions+<>c__DisplayClass4_0`1[T].<GetData>b__0 (System.String json) [0x00000] in <00000000000000000000000000000000>:0 
 at ProductGenius.Utilities.ServerFunctions+<RetrieveTextData>d__5.MoveNext () [0x00000] in <00000000000000000000000000000000>:0 
 at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00000] in <00000000000000000000000000000000>:0 
Rethrow as JsonException: Error creating 'Newtonsoft.Json.Converters.UnixDateTimeConverter'.
 at Newtonsoft.Json.Serialization.JsonTypeReflector+<>c__DisplayClass22_0.<GetCreator>b__0 (System.Object[] parameters) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonTypeReflector.GetJsonConverter (System.Object attributeProvider) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.SetPropertySettingsFromAttributes (Newtonsoft.Json.Serialization.JsonProperty property, System.Object attributeProvider, System.String name, System.Type declaringType, Newtonsoft.Json.MemberSerialization memberSerialization, System.Boolean& allowNonPublicAccess) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateProperty (System.Reflection.MemberInfo member, Newtonsoft.Json.MemberSerialization memberSerialization) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateProperties (System.Type type, Newtonsoft.Json.MemberSerialization memberSerialization) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateObjectContract (System.Type objectType) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.DefaultContractResolver.CreateContract (System.Type objectType) [0x00000] in <00000000000000000000000000000000>:0 
 at System.Collections.Concurrent.ConcurrentDictionary`2[TKey,TValue].GetOrAdd (TKey key, System.Func`2[T,TResult] valueFactory) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateList (System.Collections.IList list, Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonArrayContract contract, Newtonsoft.Json.Serialization.JsonProperty containerProperty, System.String id) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateList (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, System.Object existingValue, System.String id) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue (Newtonsoft.Json.Serialization.JsonProperty property, Newtonsoft.Json.JsonConverter propertyConverter, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerProperty, Newtonsoft.Json.JsonReader reader, System.Object target) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject (System.Object newObject, Newtonsoft.Json.JsonReader reader, Newtonsoft.Json.Serialization.JsonObjectContract contract, Newtonsoft.Json.Serialization.JsonProperty member, System.String id) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject (Newtonsoft.Json.JsonReader reader, System.Type objectType, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerMember, System.Object existingValue) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize (Newtonsoft.Json.JsonReader reader, System.Type objectType, System.Boolean checkAdditionalContent) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.JsonSerializer.DeserializeInternal (Newtonsoft.Json.JsonReader reader, System.Type objectType) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.JsonConvert.DeserializeObject (System.String value, System.Type type, Newtonsoft.Json.JsonSerializerSettings settings) [0x00000] in <00000000000000000000000000000000>:0 
 at Newtonsoft.Json.JsonConvert.DeserializeObject[T] (System.String value, Newtonsoft.Json.JsonSerializerSettings settings) [0x00000] in <00000000000000000000000000000000>:0 
 at ApplicationNameRedacted.Utilities.ServerFunctions+<>c__DisplayClass4_0`1[T].<GetData>b__0 (System.String json) [0x00000] in <00000000000000000000000000000000>:0 
 at ApplicationNameRedacted.Utilities.ServerFunctions+<RetrieveTextData>d__5.MoveNext () [0x00000] in <00000000000000000000000000000000>:0 
 at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00000] in <00000000000000000000000000000000>:0 

Steps to reproduce

1. Create a C# class that includes DateTime types and add the JsonConverter attribute above a field:
   [JsonConverter(typeof(UnixDateTimeConverter))]
2. Provide some valid Json which includes a unix timestamp value e.g.:
   "startdate":1568067791
3. Set up code to deserialise your Json to a class of the type created in step 1 using:
   Newtonsoft.Json.JsonConvert.DeserializeObject<T>
4. 'Build And Run' while targeting iOS.
5. When the code is executed in your build, the above exception is thrown and is visible in the XCode console.

[applejag]

Assuming this works on other platforms such as in the editor, and since you're targeting iOS specifically which has stricter stripping rules than other AOT platforms, I'm assuming this is due to bytecode stripping removing the UnixDateTimeConverter.

Perhaps just referring to the type is not good enough.

To fix, add this link.xml file to your Assets folder (anywhere):

<linker>
    <assembly fullname="Newtonsoft.Json">
        <type fullname="Newtonsoft.Json.Converters.UnixDateTimeConverter" preserve="all"/>
    </assembly>
</linker>

[FunkeeDan]

Assuming this works on other platforms such as in the editor, and since you're targeting iOS specifically which has stricter stripping rules than other AOT platforms, I'm assuming this is due to bytecode stripping removing the UnixDateTimeConverter.

Perhaps just referring to the type is not good enough.

To fix, add this link.xml file to your Assets folder (anywhere):

<linker>
    <assembly fullname="Newtonsoft.Json">
        <type fullname="Newtonsoft.Json.Converters.UnixDateTimeConverter" preserve="all"/>
    </assembly>
</linker>

This worked. Thanks for the workaround.

[applejag]

Cool!

Keeping this issue open as a future note to myself to add documentation about adding link.xml files.

[FunkeeDan]

The call stack above for UnixDateTimeConverter looks like it is using some reflection. I'm guessing that's why it's getting code stripped despite being referenced in my managed code. There will probably be similar issues with other JsonConverter types.

[applejag]

Yes this is a very common and known issue. What I may do instead is force the linker to include all converters by default. Instead of having to specify it explicitly.

Problem with that is then there wont be a way to strip them anymore. A price we all can pay I presume. Talking few small classes either way.