Avoid double escaping in PathString

src/Microsoft.AspNetCore.Http.Abstractions/Internal/PathStringHelper.cs

@@ -28,5 +28,20 @@ namespace Microsoft.AspNetCore.Http.Internal
         {
             return c < ValidPathChars.Length && ValidPathChars[c];
         }
+
+        public static bool IsPercentEncodedChar(string str, int index)
+        {
+            return index < str.Length - 2
+                && str[index] == '%'
+                && IsHexadecimalChar(str[index + 1])
+                && IsHexadecimalChar(str[index + 2]);
+        }
+
+        public static bool IsHexadecimalChar(char c)
+        {
+            return ('0' <= c && c <= '9')
+                || ('A' <= c && c <= 'F')
+                || ('a' <= c && c <= 'f');
+        }
     }
 }

src/Microsoft.AspNetCore.Http.Abstractions/PathString.cs

@@ -53,7 +53,7 @@ namespace Microsoft.AspNetCore.Http
         }
 
         /// <summary>
-        /// Provides the path string escaped in a way which is correct for combining into the URI representation. 
+        /// Provides the path string escaped in a way which is correct for combining into the URI representation.
         /// </summary>
         /// <returns>The escaped path value</returns>
         public override string ToString()
@@ -77,9 +77,12 @@ namespace Microsoft.AspNetCore.Http
             var start = 0;
             var count = 0;
             var requiresEscaping = false;
-            for (int i = 0; i < _value.Length; ++i)
+            var i = 0;
+
+            while (i < _value.Length)
             {
-                if (PathStringHelper.IsValidPathChar(_value[i]))
+                var isPercentEncodedChar = PathStringHelper.IsPercentEncodedChar(_value, i);
+                if (PathStringHelper.IsValidPathChar(_value[i]) || isPercentEncodedChar)
                 {
                     if (requiresEscaping)
                     {
@@ -96,7 +99,16 @@ namespace Microsoft.AspNetCore.Http
                         count = 0;
                     }
 
-                    count++;
+                    if (isPercentEncodedChar)
+                    {
+                        count += 3;
+                        i += 3;
+                    }
+                    else
+                    {
+                        count++;
+                        i++;
+                    }
                 }
                 else
                 {
@@ -116,6 +128,7 @@ namespace Microsoft.AspNetCore.Http
                     }
 
                     count++;
+                    i++;
                 }
             }
 
@@ -146,6 +159,7 @@ namespace Microsoft.AspNetCore.Http
             }
         }
 
+
         /// <summary>
         /// Returns an PathString given the path as it is escaped in the URI format. The string MUST NOT contain any
         /// value that is not a path.
@@ -279,7 +293,7 @@ namespace Microsoft.AspNetCore.Http
         }
 
         /// <summary>
-        /// Adds two PathString instances into a combined PathString value. 
+        /// Adds two PathString instances into a combined PathString value.
         /// </summary>
         /// <returns>The combined PathString value</returns>
         public PathString Add(PathString other)
@@ -297,7 +311,7 @@ namespace Microsoft.AspNetCore.Http
         }
 
         /// <summary>
-        /// Combines a PathString and QueryString into the joined URI formatted string value. 
+        /// Combines a PathString and QueryString into the joined URI formatted string value.
         /// </summary>
         /// <returns>The joined URI formatted string value</returns>
         public string Add(QueryString other)

test/Microsoft.AspNetCore.Http.Abstractions.Tests/PathStringTests.cs

@@ -195,6 +195,10 @@ namespace Microsoft.AspNetCore.Http
         [InlineData("pct-encoding", "/单行道", "/%E5%8D%95%E8%A1%8C%E9%81%93")]
         [InlineData("mixed1", "/index/单行道=(x*y)[abc]", "/index/%E5%8D%95%E8%A1%8C%E9%81%93=(x*y)%5Babc%5D")]
         [InlineData("mixed2", "/index/单行道=(x*y)[abc]_", "/index/%E5%8D%95%E8%A1%8C%E9%81%93=(x*y)%5Babc%5D_")]
+        [InlineData("encoded", "/http%3a%2f%2f[foo]%3A5000/", "/http%3a%2f%2f%5Bfoo%5D%3A5000/")]
+        [InlineData("encoded", "/http%3a%2f%2f[foo]%3A5000/%", "/http%3a%2f%2f%5Bfoo%5D%3A5000/%25")]
+        [InlineData("encoded", "/http%3a%2f%2f[foo]%3A5000/%2", "/http%3a%2f%2f%5Bfoo%5D%3A5000/%252")]
+        [InlineData("encoded", "/http%3a%2f%2f[foo]%3A5000/%2F", "/http%3a%2f%2f%5Bfoo%5D%3A5000/%2F")]
         public void ToUriComponentEscapeCorrectly(string category, string input, string expected)
         {
             var path = new PathString(input);