Port IRouteConstraint to the dispatcher project

src/Microsoft.AspNetCore.Dispatcher/ConstraintPurpose.cs

@@ -0,0 +1,21 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNetCore.Dispatcher
+{
+    /// <summary>
+    /// Represents the purpose for invoking an <see cref="IDispatcherValueConstraint"/>.
+    /// </summary>
+    public enum ConstraintPurpose
+    {
+        /// <summary>
+        /// A request URL is being processed by the dispatcher.
+        /// </summary>
+        IncomingRequest,
+
+        /// <summary>
+        /// A URL is being created by a template.
+        /// </summary>
+        TemplateExecution,
+    }
+}

src/Microsoft.AspNetCore.Dispatcher/DispatcherValueConstraintContext.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using Microsoft.AspNetCore.Http;
+
+namespace Microsoft.AspNetCore.Dispatcher
+{
+    /// <summary>
+    /// A context object for <see cref="IDispatcherValueConstraint"/>.
+    /// </summary>
+    public class DispatcherValueConstraintContext
+    {
+        private HttpContext _httpContext;
+        private DispatcherValueCollection _values;
+        private ConstraintPurpose _purpose;
+        private string _key;
+
+        /// <summary>
+        /// Creates a new <see cref="DispatcherValueConstraintContext"/>.
+        /// </summary>
+        public DispatcherValueConstraintContext()
+        {
+        }
+
+        /// <summary>
+        /// Creates a new <see cref="DispatcherValueConstraintContext"/> for the current request.
+        /// </summary>
+        /// <param name="httpContext">The <see cref="Http.HttpContext"/> associated with the current request.</param>
+        /// <param name="values">The <see cref="DispatcherValueCollection"/> for the current operation.</param>
+        /// <param name="purpose">The purpose for invoking the constraint.</param>
+        public DispatcherValueConstraintContext(HttpContext httpContext, DispatcherValueCollection values, ConstraintPurpose purpose)
+        {
+            if (httpContext == null)
+            {
+                throw new ArgumentNullException(nameof(httpContext));
+            }
+
+            if (values == null)
+            {
+                throw new ArgumentNullException(nameof(values));
+            }
+
+            HttpContext = httpContext;
+            Values = values;
+            Purpose = purpose;
+        }
+
+        /// <summary>
+        /// Gets or sets the <see cref="Http.HttpContext"/> associated with the current request.
+        /// </summary>
+        public HttpContext HttpContext
+        {
+            get => _httpContext;
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException(nameof(value));
+                }
+
+                _httpContext = value;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets the key associated with the current <see cref="IDispatcherValueConstraint"/>.
+        /// </summary>
+        public string Key
+        {
+            get => _key;
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException(nameof(value));
+                }
+
+                _key = value;
+            }
+        }
+
+        /// <summary>
+        /// Gets or sets the purpose of executing the <see cref="IDispatcherValueConstraint"/>.
+        /// </summary>
+        public ConstraintPurpose Purpose
+        {
+            get => _purpose;
+            set => _purpose = value;
+        }
+
+        /// <summary>
+        /// Gets or sets the <see cref="DispatcherValueCollection"/> associated with the current operation.
+        /// </summary>
+        public DispatcherValueCollection Values
+        {
+            get => _values;
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException(nameof(value));
+                }
+
+                _values = value;
+            }
+        }
+    }
+}

src/Microsoft.AspNetCore.Dispatcher/IDispatcherValueConstraint.cs

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+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNetCore.Dispatcher
+{
+    /// <summary>
+    /// Defines the contract that a class must implement in order to check whether a URL parameter
+    /// value is valid for a constraint.
+    /// </summary>
+    public interface IDispatcherValueConstraint
+    {
+        /// <summary>
+        /// Determines whether the current operation should succeed or fail, typically by validating one or
+        /// more values in <see cref="DispatcherValueConstraintContext.Values"/>.
+        /// </summary>
+        /// <param name="context">The <see cref="DispatcherValueConstraintContext"/> associated with the current operation.</param>
+        /// <returns><c>true</c> if the current operation should proceed; otherwise <c>false</c>.</returns>
+        bool Match(DispatcherValueConstraintContext context);
+    }
+}
+