Optimize array allocations in ValidationEndpointFilterFactory

Co-authored-by: captainsafia <1857993+captainsafia@users.noreply.github.com>

Author: Copilot

src/Http/Routing/src/ValidationEndpointFilterFactory.cs

@@ -14,6 +14,21 @@ namespace Microsoft.AspNetCore.Http.Validation;
 
 internal static class ValidationEndpointFilterFactory
 {
+    // A small struct to hold the validatable parameter details to avoid allocating arrays for parameters that don't need validation
+    private readonly struct ValidatableParameterEntry
+    {
+        public ValidatableParameterEntry(int index, IValidatableInfo parameter, string displayName)
+        {
+            Index = index;
+            Parameter = parameter;
+            DisplayName = displayName;
+        }
+
+        public int Index { get; }
+        public IValidatableInfo Parameter { get; }
+        public string DisplayName { get; }
+    }
+
     public static EndpointFilterDelegate Create(EndpointFilterFactoryContext context, EndpointFilterDelegate next)
     {
         var parameters = context.MethodInfo.GetParameters();
@@ -25,12 +40,10 @@ public static EndpointFilterDelegate Create(EndpointFilterFactoryContext context
 
         var serviceProviderIsService = context.ApplicationServices.GetService<IServiceProviderIsService>();
 
-        var parameterCount = parameters.Length;
-        var validatableParameters = new IValidatableInfo[parameterCount];
-        var parameterDisplayNames = new string[parameterCount];
-        var hasValidatableParameters = false;
+        // Use a list to only store validatable parameters instead of arrays for all parameters
+        var validatableParameters = new System.Collections.Generic.List<ValidatableParameterEntry>();
 
-        for (var i = 0; i < parameterCount; i++)
+        for (var i = 0; i < parameters.Length; i++)
         {
             // Ignore parameters that are resolved from the DI container.
             if (IsServiceParameter(parameters[i], serviceProviderIsService))
@@ -40,13 +53,14 @@ public static EndpointFilterDelegate Create(EndpointFilterFactoryContext context
 
             if (options.TryGetValidatableParameterInfo(parameters[i], out var validatableParameter))
             {
-                validatableParameters[i] = validatableParameter;
-                parameterDisplayNames[i] = GetDisplayName(parameters[i]);
-                hasValidatableParameters = true;
+                validatableParameters.Add(new ValidatableParameterEntry(
+                    i,
+                    validatableParameter,
+                    GetDisplayName(parameters[i])));
             }
         }
 
-        if (!hasValidatableParameters)
+        if (validatableParameters.Count == 0)
         {
             return next;
         }
@@ -55,18 +69,20 @@ public static EndpointFilterDelegate Create(EndpointFilterFactoryContext context
         {
             ValidateContext? validateContext = null;
 
-            for (var i = 0; i < context.Arguments.Count; i++)
+            foreach (var entry in validatableParameters)
             {
-                var validatableParameter = validatableParameters[i];
-                var displayName = parameterDisplayNames[i];
+                if (entry.Index >= context.Arguments.Count)
+                {
+                    continue;
+                }
 
-                var argument = context.Arguments[i];
-                if (argument is null || validatableParameter is null)
+                var argument = context.Arguments[entry.Index];
+                if (argument is null)
                 {
                     continue;
                 }
 
-                var validationContext = new ValidationContext(argument, displayName, context.HttpContext.RequestServices, items: null);
+                var validationContext = new ValidationContext(argument, entry.DisplayName, context.HttpContext.RequestServices, items: null);
 
                 if (validateContext == null)
                 {
@@ -81,7 +97,7 @@ public static EndpointFilterDelegate Create(EndpointFilterFactoryContext context
                     validateContext.ValidationContext = validationContext;
                 }
 
-                await validatableParameter.ValidateAsync(argument, validateContext, context.HttpContext.RequestAborted);
+                await entry.Parameter.ValidateAsync(argument, validateContext, context.HttpContext.RequestAborted);
             }
 
             if (validateContext is { ValidationErrors.Count: > 0 })