feat: #3823 add support for masking rules using Func delegates

docs/events/protection.md

@@ -17,11 +17,11 @@ builder.Services.AddMarten(opts =>
 {
     opts.Connection(builder.Configuration.GetConnectionString("marten"));
 
-    // By a single, concrete type
-    opts.Events.AddMaskingRuleForProtectedInformation<AccountChanged>(x =>
+    // By a single, concrete type (class or record)
+    opts.Events.AddMaskingRuleForProtectedInformation<AccountChanged>(x => x with
     {
         // I'm only masking a single property here, but you could do as much as you want
-        x.Name = "****";
+        Name = "****"
     });
 
     // Maybe you have an interface that multiple event types implement that would help

src/EventSourcingTests/removing_protected_information.cs

@@ -38,7 +38,23 @@ public void match_exactly_on_event_type()
         theEvents.TryMask(@event).ShouldBeTrue();
 
         started.Name.ShouldBe("****");
+    }
+
+    private record AccountChangedRecord(string FirstName, string LastName);
+
+    [Fact]
+    public void match_exactly_on_event_type_when_record()
+    {
+        theEvents.AddMaskingRuleForProtectedInformation<AccountChangedRecord>(x => x with { LastName = "****" });
+
+        var started = new AccountChangedRecord("John", "Doe");
 
+        var @event = new Event<AccountChangedRecord>(started);
+
+        theEvents.TryMask(@event).ShouldBeTrue();
+
+        started.FirstName.ShouldBe("John");
+        started.LastName.ShouldBe("****");
     }
 
     [Fact]
@@ -442,8 +458,6 @@ await theStore.Advanced.ApplyEventDataMasking(x =>
     }
 }
 
-
-
 public interface IAccountEvent
 {
     string Name { get; set; }

src/Marten/Events/EventGraph.Masking.cs

@@ -13,12 +13,25 @@ public partial class EventGraph
     /// for an event type "T" or series of event types that can be cast
     /// to "T"
     /// </summary>
-    /// <param name="action"></param>
+    /// <param name="action">Action to mask the current object</param>
     /// <typeparam name="T"></typeparam>
     public void AddMaskingRuleForProtectedInformation<T>(Action<T> action)
     {
         ArgumentNullException.ThrowIfNull(action);
-        _maskers.Add(new Masker<T>(action));
+        _maskers.Add(new ActionMasker<T>(action));
+    }
+
+    /// <summary>
+    /// Register a policy for how to remove or mask protected information
+    /// for an event type "T" or series of event types that can be cast
+    /// to "T"
+    /// </summary>
+    /// <param name="func">Function to replace the event with a masked event</param>
+    /// <typeparam name="T"></typeparam>
+    public void AddMaskingRuleForProtectedInformation<T>(Func<T,T> func)
+    {
+        ArgumentNullException.ThrowIfNull(func);
+        _maskers.Add(new FuncMasker<T>(func));
     }
 
     internal bool TryMask(IEvent e)
@@ -38,11 +51,11 @@ internal interface IMasker
     bool TryMask(IEvent @event);
 }
 
-internal class Masker<T> : IMasker where T : notnull
+internal class ActionMasker<T> : IMasker where T : notnull
 {
     private readonly Action<T> _masking;
 
-    public Masker(Action<T> masking)
+    public ActionMasker(Action<T> masking)
     {
         _masking = masking;
     }
@@ -58,3 +71,24 @@ public bool TryMask(IEvent @event)
         return false;
     }
 }
+
+internal class FuncMasker<T> : IMasker where T : notnull
+{
+    private readonly Func<T,T> _masking;
+
+    public FuncMasker(Func<T,T> masking)
+    {
+        _masking = masking;
+    }
+
+    public bool TryMask(IEvent @event)
+    {
+        if (@event is IEvent<T> e)
+        {
+            e.WithData(_masking(e.Data));
+            return true;
+        }
+
+        return false;
+    }
+}