Add option to ignore reference cycles on serialization

[jozkee]

Fixes #40099

This is a draft implementing a new API for ReferenceHandler capable of detect circularity on the input value of JsonSerializer.Serialize. A sample usage scenario would be the following:

class Node
{
    public string Description { get; set; }
    public object Next { get; set; }
}

void Test()
{
    var node = new Node { Description = "Node 1" };
    node.Next = node;
    
    var opts = new JsonSerializerOptions { ReferenceHandler = ReferenceHandler.IgnoreCycle };
    
    string json = JsonSerializer.Serialize(node, opts);
    Console.WriteLine(json); // Prints {"Description":"Node 1","Next":null}
}

Note that reference cycles are broken by null tokens in JSON.

[Dotnet-GitSync-Bot]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, to please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[eiriktsarpalis]

I think this has already been discussed in the parent issue, but as a json user, assuming I didn't want to preserve references I would prefer it if the serializer threw an exception rather than silently ignoring data (because there's likely a bug in my code).

[jozkee]

@eiriktsarpalis this is not changing the default behavior that throws an exception when MaxDepth is reached. You have to opt-in for ignoring reference loops as shown in the description's code snippet.

[steveharter]

@jozkee have you evaluated what it would take to improve the existing extensibility model to support ignore? That would either be an alternative to this feature or perhaps complementary to handle scenarios with different requirements.

[jozkee]

@steveharter I was thinking that we could add a ReferenceCycleStrategy flag that indicates the semantics that will be used and add a couple methods to ReferenceResolver for such purpose.

public abstract class ReferenceResolver
{
    protected ReferenceResolver() { }
    public abstract void AddReference(string referenceId, object value);
    public abstract string GetReference(object value, out bool alreadyExists);
    public abstract object ResolveReference(string referenceId);

+   // Pushes the value to the stack of references.
+   // Returns true if the reference already exists; otherwise, false.
+   public virtual bool PushReferenceForCycleDetection(object value);
+
+   // Pops the last reference on the stack of references once serialization of the value is complete.
+   public virtual void PopReferenceForCycleDetection();
}

public abstract class ReferenceHandler
{
    public static ReferenceHandler Preserve { get { throw null; } }
    public static ReferenceHandler IgnoreCycle { get { throw null; } }
    public abstract ReferenceResolver CreateResolver();

+   public virtual JsonReferenceCycleStrategy ReferenceCycleStrategy => JsonReferenceCycleStrategy.None;
}

+public enum JsonReferenceCycleStrategy
+{
+   // Use preserve semantics ($id and $ref) on (de)serialization.
+   None, 
+   // Use ignore semantics (treat the value as null on cycle detection) on serialization. 
+   Ignore 
+}

EDIT: As we discussed offline, this prototype breaks the single responsibility principle in ReferenceResolver.

[jozkee]

-public abstract class ReferenceResolver
+public abstract class ReferenceResolver : ReferenceResolverBase
{
    public abstract void AddReference(string referenceId, object value);
    public abstract string GetReference(object value, out bool alreadyExists);
    public abstract object ResolveReference(string referenceId);
}

+public abstract class ReferenceResolverBase {}

+public abstract class IgnoreReferenceResolver : ReferenceResolverBase 
+{
+   public abstract void PopReferenceForCycleDetection() => throw new InvalidOperationException();
+   public abstract void PushReferenceForCycleDetection(object value) => throw new InvalidOperationException();
+   public abstract bool ContainsReferenceForCycleDetection(object value) => throw new InvalidOperationException();
+}

// Binary breaking change.
-public sealed class ReferenceHandler<T> : ReferenceHandler where T : ReferenceResolver, new()
+public sealed class ReferenceHandler<T> : ReferenceHandler where T : ReferenceResolverBase, new()
{
    
-   public override ReferenceResolver CreateResolver() { throw null; }
+   public override ReferenceResolverBase CreateResolver() { throw null; }
}

public abstract partial class ReferenceHandler
{
    protected ReferenceHandler() { }
    public static ReferenceHandler Preserve { get; }
    public static ReferenceHandler IgnoreCycle { get; }
-   public abstract ReferenceResolver CreateResolver();
+   public abstract ReferenceResolverBase CreateResolver();
}

I was thinking a bit more about how an uber class could help us to keep single responsibility on each resolver and thought that we could probably add ReferenceResolverBase and make ReferenceResolver inherit from it, that way, we can keep it to work as a set of references that uses the Preserve semantics.

ReferenceResolverBase would allow us to add a new resolver (IgnoreReferenceResolver) that can be used as a stack of references and would use the ignore semantics from Newtonsoft.

However the downside of such design is that it would introduce a binary breaking change on users that already implement their own ReferenceHandler.

@steveharter @ahsonkhan @layomia @eiriktsarpalis thoughts?

[jozkee]

Update: addressed feedback and changed feature behavior to treat reference loops as null values in order to not alter the length of collections.

[jozkee]

Fixed a perf regression caused by using IsIgnoreCyclesEnabled method in order to constantly check if the feature was on.

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializer.Write.HandleMetadata.cs

Lines 91 to 92 in 2e55d73

	internal static bool IsIgnoreCyclesEnabled(JsonSerializerOptions options)
	=> !options.ReferenceHandler?.UsePreserveSemantics ?? false;

New internal field ReferenceHandlingStrategy in JsonSerializerOptions is used instead in order to perform the same check. Using a field that refreshes only when ReferenceHandler changes is cheaper than using above method.

runtime/src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

Lines 491 to 496 in 1905462

	ReferenceHandlingStrategy = value?.HandlingStrategy ?? ReferenceHandlingStrategy.None;
	}
	}
	// The cached value used to determine if ReferenceHandler should use Preserve or IgnoreCycle semanitcs or None of them.
	internal ReferenceHandlingStrategy ReferenceHandlingStrategy = ReferenceHandlingStrategy.None;

[jozkee]

BenchmarkDotNet=v0.12.1.1466-nightly, OS=Windows 10.0.18363.1316 (1909/November2019Update/19H2)
Intel Core i7-9750H CPU 2.60GHz, 1 CPU, 12 logical and 6 physical cores
.NET SDK=5.0.100
  [Host]     : .NET 5.0.0 (5.0.20.51904), X64 RyuJIT
  Job-ABOOKC : .NET 6.0.0 (42.42.42.42424), X64 RyuJIT
  Job-QJROBB : .NET 6.0.0 (42.42.42.42424), X64 RyuJIT

PowerPlanMode=00000000-0000-0000-0000-000000000000  Arguments=/p:DebugType=portable  IterationTime=250.0000 ms  
MaxIterationCount=20  MinIterationCount=15  WarmupCount=1  

Type	Method	Job	Toolchain	Mean	Error	StdDev	Median	Min	Max	Ratio	MannWhitney(3ms)	Gen 0	Gen 1	Gen 2	Allocated
WriteJson<IndexViewModel>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	17,076.1 ns	172.47 ns	161.33 ns	17,057.3 ns	16,803.3 ns	17,401.4 ns	1.01	Same	2.0292	0.0676	-	13,024 B
WriteJson<IndexViewModel>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	16,887.4 ns	99.72 ns	93.27 ns	16,875.5 ns	16,746.1 ns	17,076.6 ns	1.00	Base	2.0380	0.0679	-	13,024 B
WriteJson<Int32>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	122.9 ns	1.55 ns	1.37 ns	123.1 ns	119.2 ns	125.0 ns	1.01	Same	0.0289	-	-	184 B
WriteJson<Int32>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	121.1 ns	1.78 ns	1.48 ns	121.1 ns	117.9 ns	123.5 ns	1.00	Base	0.0289	-	-	184 B
WriteJson<LargeStructWithProperties>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	627.5 ns	4.92 ns	4.60 ns	627.4 ns	621.2 ns	636.3 ns	1.01	Same	0.0578	-	-	376 B
WriteJson<LargeStructWithProperties>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	624.2 ns	4.57 ns	4.28 ns	624.6 ns	617.5 ns	632.7 ns	1.00	Base	0.0581	-	-	376 B
WriteJson<Location>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	761.1 ns	4.59 ns	4.07 ns	760.9 ns	755.2 ns	770.5 ns	0.98	Same	0.0611	-	-	384 B
WriteJson<Location>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	778.0 ns	7.14 ns	6.68 ns	778.5 ns	768.6 ns	792.3 ns	1.00	Base	0.0596	-	-	384 B
WriteJson<LoginViewModel>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	314.8 ns	2.71 ns	2.54 ns	314.4 ns	310.9 ns	320.0 ns	0.98	Same	0.0410	-	-	264 B
WriteJson<LoginViewModel>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	320.0 ns	1.60 ns	1.42 ns	320.2 ns	317.1 ns	323.1 ns	1.00	Base	0.0416	-	-	264 B
WriteJson<MyEventsListerViewModel>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	413,696.7 ns	3,250.95 ns	3,040.94 ns	412,356.4 ns	410,011.2 ns	418,388.0 ns	1.01	Same	29.6053	4.9342	-	191,665 B
WriteJson<MyEventsListerViewModel>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	408,065.2 ns	3,297.89 ns	3,084.85 ns	408,330.6 ns	403,268.6 ns	412,867.3 ns	1.00	Base	28.8462	4.8077	-	191,705 B
WriteJson<SimpleStructWithProperties>	SerializeToUtf8Bytes	Job-ABOOKC	\runtime2\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	232.2 ns	1.87 ns	1.75 ns	231.9 ns	229.1 ns	235.3 ns	1.01	Same	0.0361	-	-	232 B
WriteJson<SimpleStructWithProperties>	SerializeToUtf8Bytes	Job-QJROBB	\runtime\artifacts\bin\testhost\net6.0-windows-Release-x64\shared\Microsoft.NETCore.App\6.0.0\CoreRun.exe	230.6 ns	2.59 ns	2.42 ns	230.4 ns	227.7 ns	236.1 ns	1.00	Base	0.0366	-	-	232 B

[layomia]

For this and the following collection-related types, I notice that the element types are all object. Do we have any with strongly typed class-type, value-type, and nullable-value-type elements?

[jozkee]

I added more types that contain a property with object or a concrete type. It should cover boxed classes, non-boxed classes and boxed structs.

I am not testing non-boxed value types since those are ignored/never tracked in the stack of references and Nullable<T> can't be boxed.

[layomia]

Does Newtonsoft.Json have the same behavior here?

[jozkee]

Yes, Newtonsoft also detects loops in the elements of the extension data.

[layomia]

LGTM

[jozkee]

CI issues are unrelated: #39244, #39244.

[jeffhandley]

Awesome! 💯

@jozkee, please add a comment to dotnet/core#5889 to capture this new feature in the Preview 2 release notes.

[ericsampson]

@jozkee thank you very much, I know there was a lot of churn/heat regarding this :)

[MattGal]

CI issues are unrelated: #39244, #39244.

@jozkee based off the log you linked, please investigate immediately and back out your changes if appropriate. dotnet.exe exiting with 0xc0000409 (STATUS_STACK_BUFFER_OVERRUN) is not a helix failure, rather a crash with a buffer overrun

[jozkee]

@MattGal I have sent #48464 which build on top of these changes, will expect to not hit those errors in the new PR, otherwise I will investigate if they are related to this change.

[MattGal]

@MattGal I have sent #48464 which build on top of these changes, will expect to not hit those errors in the new PR, otherwise I will investigate if they are related to this change.

On further investigation this really seems like a payload building problem, since it didn't repro on the same combos in master after you merged. Probably can ignore, but please do be cautious about this sort of thing as it wasn't related to the linked issues.