From e22702891dbbb2f5a9ed96d1d3592bbfbff19fa4 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Mon, 29 Apr 2019 01:28:48 +0100
Subject: [PATCH] Pass catchAll ValueTuple via in (#9807)

---
 src/Http/Routing/src/Matching/Candidate.cs  |  2 +-
 src/Http/Routing/src/Matching/DfaMatcher.cs | 13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/Http/Routing/src/Matching/Candidate.cs b/src/Http/Routing/src/Matching/Candidate.cs
index 4493293251..cd390c4980 100644
--- a/src/Http/Routing/src/Matching/Candidate.cs
+++ b/src/Http/Routing/src/Matching/Candidate.cs
@@ -68,7 +68,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             int score,
             KeyValuePair<string, object>[] slots,
             (string parameterName, int segmentIndex, int slotIndex)[] captures,
-            (string parameterName, int segmentIndex, int slotIndex) catchAll,
+            in (string parameterName, int segmentIndex, int slotIndex) catchAll,
             (RoutePatternPathSegment pathSegment, int segmentIndex)[] complexSegments,
             KeyValuePair<string, IRouteConstraint>[] constraints)
         {
diff --git a/src/Http/Routing/src/Matching/DfaMatcher.cs b/src/Http/Routing/src/Matching/DfaMatcher.cs
index 441e53d556..e41fc44f6d 100644
--- a/src/Http/Routing/src/Matching/DfaMatcher.cs
+++ b/src/Http/Routing/src/Matching/DfaMatcher.cs
@@ -76,7 +76,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
             // This is a fast path for single candidate, 0 policies and default selector
             if (candidateCount == 1 && policyCount == 0 && _isDefaultEndpointSelector)
             {
-                ref var candidate = ref candidates[0];
+                ref readonly var candidate = ref candidates[0];
 
                 // Just strict path matching
                 if (candidate.Flags == Candidate.CandidateFlags.None)
@@ -110,7 +110,7 @@ namespace Microsoft.AspNetCore.Routing.Matching
                 // Reminder!
                 // candidate: readonly data about the endpoint and how to match
                 // state: mutable storarge for our processing
-                ref var candidate = ref candidates[i];
+                ref readonly var candidate = ref candidates[i];
                 ref var state = ref candidateState[i];
                 state = new CandidateState(candidate.Endpoint, candidate.Score);
 
@@ -249,13 +249,16 @@ namespace Microsoft.AspNetCore.Routing.Matching
 
         private void ProcessCatchAll(
             KeyValuePair<string, object>[] slots,
-            (string parameterName, int segmentIndex, int slotIndex) catchAll,
+            in (string parameterName, int segmentIndex, int slotIndex) catchAll,
             string path,
             ReadOnlySpan<PathSegment> segments)
         {
-            if (segments.Length > catchAll.segmentIndex)
+            // Read segmentIndex to local both to skip double read from stack value
+            // and to use the same in-bounds validated varaible to access the array.
+            var segmentIndex = catchAll.segmentIndex;
+            if ((uint)segmentIndex < (uint)segments.Length)
             {
-                var segment = segments[catchAll.segmentIndex];
+                var segment = segments[segmentIndex];
                 slots[catchAll.slotIndex] = new KeyValuePair<string, object>(
                     catchAll.parameterName,
                     path.Substring(segment.Start));