BinaryFormatter exception in ConfigurationManager when accessing non-existing key

[steinmal]

.NET 6
Console application

Why does this create an exception regarding BinaryFormatter not supported?
I am not using any binary formatter, and SettingsSerializeAs is set to XML.

using System.Configuration;

var provider = new LocalFileSettingsProvider();
var context = new SettingsContext();

var attributes = new SettingsAttributeDictionary();
var attr = new UserScopedSettingAttribute();
attributes.Add(attr.TypeId, attr);

var prop = new SettingsProperty(
"Test",
typeof(bool),
provider,
false,
default(bool),
SettingsSerializeAs.Xml,
attributes,
false,
false);

var propertyCollection = new SettingsPropertyCollection { prop };
var propertyValueCollection = provider.GetPropertyValues(context, propertyCollection);
var pv = propertyValueCollection["Test"];
var value = pv.PropertyValue;

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[danmoseley]

Can you please share the call stack.

[steinmal]

The exception:
System.NotSupportedException HResult=0x80131515 Message=BinaryFormatter serialization is obsolete and should not be used. See https://aka.ms/binaryformatter for more information. Source=System.Configuration.ConfigurationManager StackTrace: at System.Configuration.SettingsPropertyValue.Deserialize() at System.Configuration.SettingsPropertyValue.get_PropertyValue() at Program.<Main>$(String[] args) in C:\Users\****\source\repos\TestPreference\Program.cs:line 24

[ericstj]

I can repro, looks to me like this bug was introduced here:
2fb544c#diff-5adbe04e45ed985efd15df67801b9b845ac8453357d74478b2124bbeb1d85c6fR136
Between the 5.0.0 and 6.0.0 version of ConfigurationManger package.

Previously this would actually throw a cast exception when trying to cast to byte[]

runtime/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/SettingsPropertyValue.cs

Line 99 in 05a8c76

using (MemoryStream ms = new MemoryStream((byte[])SerializedValue))

That would be caught and swallowed:

runtime/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/SettingsPropertyValue.cs

Lines 106 to 125 in 05a8c76

	catch (Exception exception)
	{
	try
	{
	if (IsHostedInAspnet())
	{
	object[] args = new object[] { Property, this, exception };
	const string webBaseEventTypeName = "System.Web.Management.WebBaseEvent, System.Web";
	Type type = Type.GetType(webBaseEventTypeName, true);
	type.InvokeMember("RaisePropertyDeserializationWebErrorEvent",
	BindingFlags.NonPublic | BindingFlags.Static | BindingFlags.InvokeMethod,
	null, null, args, CultureInfo.InvariantCulture);
	}
	}
	catch
	{
	}
	}

And then the deserialize method would fall back to assigning from the DefaultValue

runtime/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/SettingsPropertyValue.cs

Lines 142 to 145 in 05a8c76

	if (!(Property.DefaultValue is string))
	{
	value = Property.DefaultValue;
	}

This is happening because on construction of the SettingsPropertyValue the LocalFileSettingsProvider applies the default value as SerializedValue:

runtime/src/libraries/System.Configuration.ConfigurationManager/src/System/Configuration/LocalFileSettingsProvider.cs

Lines 151 to 154 in 05a8c76

	else if (setting.DefaultValue != null)
	{
	value.SerializedValue = setting.DefaultValue;
	}

This is odd, but seems to be long standing existing behavior.

I think we can fix this by doing a type check up front on byte[] and avoid going down the BinaryFormatter path if the SerializedValue is not a byte[]. That will still introduce an exception where one wasn't before if 1) BinaryFormatter is disabled 2) when BinaryFormatter was enabled it would have failed to deserialize and throw an exception (which would have been swallowed). I suspect this is rare enough to allow it and prioritize exposing an exception when BinaryFormatter was disabled and might have been needed.

[ericstj]

I'll go ahead and fix this since I repro'ed it and made the fix. Just working on a test.