add benchmarks for IsRelationshipPath

Author: jaredcnance

benchmarks/BenchmarkDotNet.Artifacts/results/Benchmarks.JsonApiContext.PathIsRelationship_Benchmarks-report-github.md

@@ -0,0 +1,12 @@
+```ini
+BenchmarkDotNet=v0.10.10, OS=Mac OS X 10.12
+Processor=Intel Core i5-5257U CPU 2.70GHz (Broadwell), ProcessorCount=4
+.NET Core SDK=2.1.4
+  [Host]     : .NET Core 2.0.5 (Framework 4.6.0.0), 64bit RyuJIT
+  DefaultJob : .NET Core 2.0.5 (Framework 4.6.0.0), 64bit RyuJIT
+```
+
+| Method     |      Mean |      Error |     StdDev |  Gen 0 | Allocated |
+| ---------- | --------: | ---------: | ---------: | -----: | --------: |
+| UsingSplit | 421.08 ns | 19.3905 ns | 54.0529 ns | 0.4725 |     744 B |
+| Current    |  52.23 ns |  0.8052 ns |  0.7532 ns |      - |       0 B |

benchmarks/JsonApiContext/PathIsRelationship_Benchmarks.cs

@@ -0,0 +1,24 @@
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Attributes.Exporters;
+
+namespace Benchmarks.JsonApiContext
+{
+    [MarkdownExporter, MemoryDiagnoser]
+    public class PathIsRelationship_Benchmarks
+    {
+        private const string PATH = "https://example.com/api/v1/namespace/articles/relationships/author/";
+
+        [Benchmark]
+        public void Current() 
+            => JsonApiDotNetCore.Services.JsonApiContext.PathIsRelationship(PATH);
+
+        [Benchmark]
+        public void UsingSplit() => UsingSplitImpl(PATH);
+
+        private bool UsingSplitImpl(string path)
+        {
+            var split = path.Split('/');
+            return split[split.Length - 2] == "relationships";
+        }
+    }
+}

benchmarks/Program.cs

@@ -1,4 +1,5 @@
 using BenchmarkDotNet.Running;
+using Benchmarks.JsonApiContext;
 using Benchmarks.LinkBuilder;
 using Benchmarks.Query;
 using Benchmarks.RequestMiddleware;
@@ -12,7 +13,8 @@ static void Main(string[] args) {
                 typeof(JsonApiSerializer_Benchmarks),
                 typeof(QueryParser_Benchmarks),
                 typeof(LinkBuilder_GetNamespaceFromPath_Benchmarks),
-                typeof(ContainsMediaTypeParameters_Benchmarks)
+                typeof(ContainsMediaTypeParameters_Benchmarks),
+                typeof(PathIsRelationship_Benchmarks)
             });
             switcher.Run(args);
         }

benchmarks/RequestMiddleware/ContainsMediaTypeParameters_Benchmarks.cs

@@ -1,4 +1,3 @@
-using System;
 using BenchmarkDotNet.Attributes;
 using BenchmarkDotNet.Attributes.Exporters;
 using JsonApiDotNetCore.Internal;

src/JsonApiDotNetCore/Services/JsonApiContext.cs

@@ -1,9 +1,7 @@
 using System;
 using System.Collections.Generic;
-using System.Linq;
 using JsonApiDotNetCore.Builders;
 using JsonApiDotNetCore.Configuration;
-using JsonApiDotNetCore.Extensions;
 using JsonApiDotNetCore.Internal;
 using JsonApiDotNetCore.Internal.Generics;
 using JsonApiDotNetCore.Internal.Query;
@@ -65,23 +63,53 @@ public IJsonApiContext ApplyContext<T>(object controller)
                 throw new JsonApiException(500, $"A resource has not been properly defined for type '{typeof(T)}'. Ensure it has been registered on the ContextGraph.");
 
             var context = _httpContextAccessor.HttpContext;
-            var requestPath = context.Request.Path.Value;
 
             if (context.Request.Query.Count > 0)
             {
                 QuerySet = _queryParser.Parse(context.Request.Query);
                 IncludedRelationships = QuerySet.IncludedRelationships;
             }
 
-            var linkBuilder = new LinkBuilder(this);
-            BasePath = linkBuilder.GetBasePath(context, _controllerContext.RequestEntity.EntityName);
+            BasePath = new LinkBuilder(this).GetBasePath(context, _controllerContext.RequestEntity.EntityName);
             PageManager = GetPageManager();
-
-            var pathSpans = requestPath.SpanSplit('/');
-            IsRelationshipPath = pathSpans[pathSpans.Count - 2].ToString() == "relationships";
+            IsRelationshipPath = PathIsRelationship(context.Request.Path.Value);
 
             return this;
         }
+
+        internal static bool PathIsRelationship(string requestPath)
+        {
+            // while(!Debugger.IsAttached) { Thread.Sleep(1000); }
+            const string relationships = "relationships";
+            const char pathSegmentDelimiter = '/';
+
+            var span = requestPath.AsSpan();
+            
+            // we need to iterate over the string, from the end,
+            // checking whether or not the 2nd to last path segment
+            // is "relationships"
+            // -2 is chosen in case the path ends with '/'
+            for(var i = requestPath.Length - 2; i >= 0; i--)
+            {
+                // if there are not enough characters left in the path to 
+                // contain "relationships"
+                if(i < relationships.Length) 
+                    return false;
+
+                // we have found the first instance of '/'
+                if(span[i] == pathSegmentDelimiter)
+                {
+                    // in the case of a "relationships" route, the next
+                    // path segment will be "relationships"
+                    return (
+                        span.Slice(i - relationships.Length, relationships.Length)
+                            .SequenceEqual(relationships.AsSpan())
+                    );
+                }
+            }
+
+            return false;
+        }
 
         private PageManager GetPageManager()
         {