Add support for optional parameters in Blazor routes

src/Components/Components/src/Routing/OptionalTypeRouteConstraint.cs

@@ -0,0 +1,45 @@
+// 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.Components.Routing
+{
+    /// <summary>
+    /// A route constraint that allows the value to be null or parseable as the specified
+    /// type.
+    /// </summary>
+    /// <typeparam name="T">The type to which the value must be parseable.</typeparam>
+    internal class OptionalTypeRouteConstraint<T> : RouteConstraint
+    {
+        public delegate bool TryParseDelegate(string str, out T result);
+
+        private readonly TryParseDelegate _parser;
+
+        public OptionalTypeRouteConstraint(TryParseDelegate parser)
+        {
+            _parser = parser;
+        }
+
+        public override bool Match(string pathSegment, out object convertedValue)
+        {
+            // Unset values are set to null in the Parameters object created in
+            // the RouteContext. To match this pattern, unset optional parmeters
+            // are converted to null.
+            if (string.IsNullOrEmpty(pathSegment))
+            {
+                convertedValue = null;
+                return true;
+            }
+
+            if (_parser(pathSegment, out var result))
+            {
+                convertedValue = result;
+                return true;
+            }
+            else
+            {
+                convertedValue = null;
+                return false;
+            }
+        }
+    }
+}

src/Components/Components/src/Routing/RouteConstraint.cs

@@ -47,32 +47,64 @@ public static RouteConstraint Parse(string template, string segment, string cons
             }
         }
 
+        /// <summary>
+        /// Creates a structured RouteConstraint object given a string that contains
+        /// the route constraint. A constraint is the place after the colon in a
+        /// parameter definition, for example `{age:int?}`.
+        ///
+        /// If the constraint denotes an optional, this method will return an
+        /// <see cref="OptionalTypeRouteConstraint{T}" /> which handles the appropriate checks.
+        /// </summary>
+        /// <param name="constraint">String representation of the constraint</param>
+        /// <returns>Type-specific RouteConstraint object</returns>
         private static RouteConstraint CreateRouteConstraint(string constraint)
         {
             switch (constraint)
             {
                 case "bool":
                     return new TypeRouteConstraint<bool>(bool.TryParse);
+                case "bool?":
+                    return new OptionalTypeRouteConstraint<bool>(bool.TryParse);
                 case "datetime":
                     return new TypeRouteConstraint<DateTime>((string str, out DateTime result)
                         => DateTime.TryParse(str, CultureInfo.InvariantCulture, DateTimeStyles.None, out result));
+                case "datetime?":
+                    return new OptionalTypeRouteConstraint<DateTime>((string str, out DateTime result)
+                        => DateTime.TryParse(str, CultureInfo.InvariantCulture, DateTimeStyles.None, out result));
                 case "decimal":
                     return new TypeRouteConstraint<decimal>((string str, out decimal result)
                         => decimal.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
+                case "decimal?":
+                    return new OptionalTypeRouteConstraint<decimal>((string str, out decimal result)
+                        => decimal.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
                 case "double":
                     return new TypeRouteConstraint<double>((string str, out double result)
                         => double.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
+                case "double?":
+                    return new OptionalTypeRouteConstraint<double>((string str, out double result)
+                        => double.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
                 case "float":
                     return new TypeRouteConstraint<float>((string str, out float result)
                         => float.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
+                case "float?":
+                    return new OptionalTypeRouteConstraint<float>((string str, out float result)
+                        => float.TryParse(str, NumberStyles.Number, CultureInfo.InvariantCulture, out result));
                 case "guid":
                     return new TypeRouteConstraint<Guid>(Guid.TryParse);
+                case "guid?":
+                    return new OptionalTypeRouteConstraint<Guid>(Guid.TryParse);
                 case "int":
                     return new TypeRouteConstraint<int>((string str, out int result)
                         => int.TryParse(str, NumberStyles.Integer, CultureInfo.InvariantCulture, out result));
+                case "int?":
+                    return new OptionalTypeRouteConstraint<int>((string str, out int result)
+                        => int.TryParse(str, NumberStyles.Integer, CultureInfo.InvariantCulture, out result));
                 case "long":
                     return new TypeRouteConstraint<long>((string str, out long result)
                         => long.TryParse(str, NumberStyles.Integer, CultureInfo.InvariantCulture, out result));
+                case "long?":
+                    return new OptionalTypeRouteConstraint<long>((string str, out long result)
+                        => long.TryParse(str, NumberStyles.Integer, CultureInfo.InvariantCulture, out result));
                 default:
                     return null;
             }

src/Components/Components/src/Routing/RouteEntry.cs

@@ -2,8 +2,10 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Linq;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Text;
 
 namespace Microsoft.AspNetCore.Components.Routing
 {
@@ -25,23 +27,52 @@ public RouteEntry(RouteTemplate template, Type handler, string[] unusedRoutePara
 
         internal void Match(RouteContext context)
         {
-            if (Template.Segments.Length != context.Segments.Length)
+            // If there are no optional segments on the route and the length of the route
+            // and the template do not match, then there is no chance of this matching and
+            // we can bail early.
+            if (Template.OptionalSegmentsCount == 0 && Template.Segments.Length != context.Segments.Length)
             {
                 return;
             }
 
             // Parameters will be lazily initialized.
             Dictionary<string, object> parameters = null;
+            var numMatchingSegments = 0;
             for (var i = 0; i < Template.Segments.Length; i++)
             {
                 var segment = Template.Segments[i];
-                var pathSegment = context.Segments[i];
+
+                // If the template contains more segments than the path, then
+                // we may need to break out of this for-loop. This can happen
+                // in one of two cases:
+                //
+                // (1) If we are comparing a literal route with a literal template
+                // and the route is shorter than the template.
+                // (2) If we are comparing a template where the last value is an optional
+                // parameter that the route does not provide.
+                if (i >= context.Segments.Length)
+                {
+                    // If we are under condition (1) above then we can stop evaluating
+                    // matches on the rest of this template.
+                    if (!segment.IsParameter && !segment.IsOptional)
+                    {
+                        break;
+                    }
+                }
+
+                string pathSegment = null;
+                if (i < context.Segments.Length)
+                {
+                    pathSegment = context.Segments[i];
+                }
+
                 if (!segment.Match(pathSegment, out var matchedParameterValue))
                 {
                     return;
                 }
                 else
                 {
+                    numMatchingSegments++;
                     if (segment.IsParameter)
                     {
                         parameters ??= new Dictionary<string, object>(StringComparer.Ordinal);
@@ -62,8 +93,32 @@ internal void Match(RouteContext context)
                 }
             }
 
-            context.Parameters = parameters;
-            context.Handler = Handler;
+            // We track the number of segments in the template that matched
+            // against this particular route then only select the route that
+            // matches the most number of segments on the route that was passed.
+            // This check is an exactness check that favors the more precise of
+            // two templates in the event that the following route table exists.
+            //  Route 1: /{anythingGoes}
+            //  Route 2: /users/{id:int}
+            // And the provided route is `/users/1`. We want to choose Route 2
+            // over Route 1.
+            // Furthermore, literal routes are preferred over parameterized routes.
+            // If the two routes below are registered in the route table.
+            // Route 1: /users/1
+            // Route 2: /users/{id:int}
+            // And the provided route is `/users/1`. We want to choose Route 1 over
+            // Route 2.
+            var allRouteSegmentsMatch = numMatchingSegments >= context.Segments.Length;
+            // Checking that all route segments have been matches does not suffice if we are
+            // comparing literal templates with literal routes. For example, the template
+            // `/this/is/a/template` and the route `/this/`. In that case, we want to ensure
+            // that all non-optional segments have matched as well.
+            var allNonOptionalSegmentsMatch = numMatchingSegments >= (Template.Segments.Length - Template.OptionalSegmentsCount);
+            if (allRouteSegmentsMatch && allNonOptionalSegmentsMatch)
+            {
+                context.Parameters = parameters;
+                context.Handler = Handler;
+            }
         }
     }
 }

src/Components/Components/src/Routing/RouteTableFactory.cs

@@ -142,6 +142,17 @@ internal static int RouteComparison(RouteEntry x, RouteEntry y)
 
                     if (xSegment.IsParameter)
                     {
+                        // Always favor non-optional parameters over optional ones
+                        if (!xSegment.IsOptional && ySegment.IsOptional)
+                        {
+                            return -1;
+                        }
+
+                        if (xSegment.IsOptional && !ySegment.IsOptional)
+                        {
+                            return 1;
+                        }
+
                         if (xSegment.Constraints.Length > ySegment.Constraints.Length)
                         {
                             return -1;

src/Components/Components/src/Routing/RouteTemplate.cs

@@ -3,6 +3,7 @@
 
 
 using System.Diagnostics;
+using System.Linq;
 
 namespace Microsoft.AspNetCore.Components.Routing
 {
@@ -13,10 +14,13 @@ public RouteTemplate(string templateText, TemplateSegment[] segments)
         {
             TemplateText = templateText;
             Segments = segments;
+            OptionalSegmentsCount = segments.Count(template => template.IsOptional);
         }
 
         public string TemplateText { get; }
 
         public TemplateSegment[] Segments { get; }
+
+        public int OptionalSegmentsCount { get; }
     }
 }

src/Components/Components/src/Routing/TemplateParser.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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;
 
@@ -13,21 +13,20 @@ namespace Microsoft.AspNetCore.Components.Routing
     // simple parameters from it.
     // Some differences with ASP.NET Core routes are:
     // * We don't support catch all parameter segments.
-    // * We don't support optional parameter segments.
     // * We don't support complex segments.
     // The things that we support are:
     // * Literal path segments. (Like /Path/To/Some/Page)
     // * Parameter path segments (Like /Customer/{Id}/Orders/{OrderId})
     internal class TemplateParser
     {
         public static readonly char[] InvalidParameterNameCharacters =
-            new char[] { '*', '?', '{', '}', '=', '.' };
+            new char[] { '*', '{', '}', '=', '.' };
 
         internal static RouteTemplate ParseTemplate(string template)
         {
             var originalTemplate = template;
             template = template.Trim('/');
-            if (template == "")
+            if (template == string.Empty)
             {
                 // Special case "/";
                 return new RouteTemplate("/", Array.Empty<TemplateSegment>());
@@ -89,9 +88,10 @@ internal static RouteTemplate ParseTemplate(string template)
                 for (int j = i + 1; j < templateSegments.Length; j++)
                 {
                     var nextSegment = templateSegments[j];
-                    if (!nextSegment.IsParameter)
+
+                    if (currentSegment.IsOptional && !nextSegment.IsOptional)
                     {
-                        continue;
+                        throw new InvalidOperationException($"Invalid template '{template}'. Non-optional parameters or literal routes cannot appear after optional parameters.");
                     }
 
                     if (string.Equals(currentSegment.Value, nextSegment.Value, StringComparison.OrdinalIgnoreCase))

src/Components/Components/src/Routing/TemplateSegment.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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;
@@ -12,9 +12,29 @@ public TemplateSegment(string template, string segment, bool isParameter)
         {
             IsParameter = isParameter;
 
+            // Process segments that are not parameters or do not contain
+            // a token separating a type constraint.
             if (!isParameter || segment.IndexOf(':') < 0)
             {
-                Value = segment;
+                // Set the IsOptional flag to true for segments that contain
+                // a parameter with no type constraints but optionality set
+                // via the '?' token.
+                if (segment.IndexOf('?') == segment.Length - 1)
+                {
+                    IsOptional = true;
+                    Value = segment.Substring(0, segment.Length - 1);
+                }
+                // If the `?` optional marker shows up in the segment but not at the very end,
+                // then throw an error.
+                else if (segment.IndexOf('?') >= 0 && segment.IndexOf('?') != segment.Length - 1)
+                {
+                    throw new ArgumentException($"Malformed parameter '{segment}' in route '{template}'. '?' character can only appear at the end of parameter name.");
+                }
+                else
+                {
+                    Value = segment;
+                }
+
                 Constraints = Array.Empty<RouteConstraint>();
             }
             else
@@ -25,6 +45,10 @@ public TemplateSegment(string template, string segment, bool isParameter)
                     throw new ArgumentException($"Malformed parameter '{segment}' in route '{template}' has no name before the constraints list.");
                 }
 
+                // Set the IsOptional flag to true if any type constraints
+                // for this parameter are designated as optional.
+                IsOptional = tokens.Skip(1).Any(token => token.EndsWith("?"));
+
                 Value = tokens[0];
                 Constraints = tokens.Skip(1)
                     .Select(token => RouteConstraint.Parse(template, segment, token))
@@ -38,6 +62,8 @@ public TemplateSegment(string template, string segment, bool isParameter)
 
         public bool IsParameter { get; }
 
+        public bool IsOptional { get;  }
+
         public RouteConstraint[] Constraints { get; }
 
         public bool Match(string pathSegment, out object matchedParameterValue)

src/Components/Components/test/Routing/RouteConstraintTest.cs

@@ -32,5 +32,15 @@ public void Parse_CachesCreatedConstraint_ForSameKind()
             // Assert
             Assert.Same(original, another);
         }
+
+        [Fact]
+        public void Parse_DoesNotThrowIfOptionalConstraint()
+        {
+            // Act
+            var exceptions = Record.Exception(() => RouteConstraint.Parse("ignore", "ignore", "int?"));
+
+            // Assert
+            Assert.Null(exceptions);
+        }
     }
 }