Attempted to access an element as a type incompatible with the array.

[n9]

Version: 2.12.27 (current in nuget, but not as a release in this repo)
Caller: .NET 6 (Windows)
Target: .NET 6 (Android)

Exception: StreamJsonRpc.RemoteInvocationException
ErrorCode: -32000 (StreamJsonRpc.Protocol.JsonRpcErrorCode.InvocationError)
ErrorData.TypeName: System.ArrayTypeMismatchException
ErrorData.Message: Attempted to access an element as a type incompatible with the array.
ErrorData.Stack:

   at StreamJsonRpc.TargetMethod.TryGetArguments(JsonRpcRequest request, MethodSignature method, Span`1 arguments)
   at StreamJsonRpc.TargetMethod..ctor(JsonRpcRequest request, List`1 candidateMethodTargets, SynchronizationContext fallbackSynchronizationContext)
   at StreamJsonRpc.Reflection.RpcTargetInfo.TryGetTargetMethod(JsonRpcRequest request, TargetMethod& targetMethod)
   at StreamJsonRpc.JsonRpc.DispatchIncomingRequestAsync(JsonRpcRequest request)

Signature of the called method:

Task Start();

Not sure how mono is currently integrated into .NET 6 (for Android), there is already one ticket with the same error message: #387

[n9]

@AArnott Could you please release preview/testing nuget with modified "mono" check (that will also work on Android).

The current check is not working on Android:

vs-streamjsonrpc/src/StreamJsonRpc/Utilities.cs

Line 16 in d691f42

internal static bool IsRunningOnMono => Type.GetType("Mono.Runtime") is not null;

But the following check is:

Type.GetType("Mono.RuntimeStructs") != null

Source:

https://github.com/dotnet/runtime/blob/9e1350eb6d8d6018d599b7fefbae6805dbd420ea/src/libraries/Common/tests/TestUtilities/System/PlatformDetection.cs#L30

[n9]

The issue appears only when the method has no parameters. "Mono" (.net 6 on android) returns in that case RuntimeParameterInfo[] instead of ParameterInfo[].

In that case, AsSpan will fail, but ReadOnlySpan will work:

static void Main()
{
        var type = Type.GetType("System.Object");
        TestMethod(type, "ReferenceEquals");
        TestMethod(type, "ToString");
}

static void TestMethod(Type type, string name)
{
        var method = type.GetMethod(name);
        var parameters = method.GetParameters();
        new ReadOnlySpan<ParameterInfo>(parameters, 0, 0);
        Span<ParameterInfo> sp = parameters.AsSpan(0, 0); // <- this will fail on "mono" in case of method with 0 parameters
}

The following example will fail also in "vanilla" .net 6 (on windows):

class A { }
class B : A { }

void Main()
{
	new ReadOnlySpan<A>(Array.Empty<B>());
	((A[])Array.Empty<B>()).AsSpan(); // <- error here
}

I think it is correct that AsSpan will fail in that case.

So, the fix should not improve "mono" detection, but use ReadOnlySpan<T> instead of AsSpan.

Do you agree?

[AArnott]

Excellent analysis, @n9. I'm preparing the change now.