Handle subtype with suffix being a subtype without a suffix (#1027)

src/Microsoft.Net.Http.Headers/MediaTypeHeaderValue.cs

@@ -650,6 +650,7 @@ namespace Microsoft.Net.Http.Headers
             {
                 return true;
             }
+
             if (set.Suffix.HasValue)
             {
                 if (Suffix.HasValue)
@@ -663,7 +664,10 @@ namespace Microsoft.Net.Http.Headers
             }
             else
             {
-                return set.SubType.Equals(SubType, StringComparison.OrdinalIgnoreCase);
+                // If this subtype or suffix matches the subtype of the set,
+                // it is considered a subtype.
+                // Ex: application/json > application/val+json
+                return MatchesEitherSubtypeOrSuffix(set);
             }
         }
 
@@ -673,6 +677,12 @@ namespace Microsoft.Net.Http.Headers
                 set.SubTypeWithoutSuffix.Equals(SubTypeWithoutSuffix, StringComparison.OrdinalIgnoreCase);
         }
 
+        private bool MatchesEitherSubtypeOrSuffix(MediaTypeHeaderValue set)
+        {
+            return set.SubType.Equals(SubType, StringComparison.OrdinalIgnoreCase) ||
+                set.SubType.Equals(Suffix, StringComparison.OrdinalIgnoreCase);
+        }
+
         private bool MatchesParameters(MediaTypeHeaderValue set)
         {
             if (set._parameters != null && set._parameters.Count != 0)

test/Microsoft.Net.Http.Headers.Tests/MediaTypeHeaderValueTest.cs

@@ -750,6 +750,8 @@ namespace Microsoft.Net.Http.Headers
         [InlineData("application/entity+json", "application/entity+json")]
         [InlineData("application/*+json", "application/entity+json")]
         [InlineData("application/*+json", "application/*+json")]
+        [InlineData("application/json", "application/problem+json")]
+        [InlineData("application/json", "application/vnd.restful+json")]
         [InlineData("application/*", "application/*+JSON")]
         [InlineData("application/vnd.github+json", "application/vnd.github+json")]
         [InlineData("application/*", "application/entity+JSON")]
@@ -774,6 +776,7 @@ namespace Microsoft.Net.Http.Headers
         [InlineData("application/*+*", "application/json")]
         [InlineData("application/entity+*", "application/entity+json")] // We don't allow suffixes to be wildcards
         [InlineData("application/*+*", "application/entity+json")] // We don't allow suffixes to be wildcards
+        [InlineData("application/entity+json", "application/entity")]
         public void IsSubSetOfWithSuffixes_NegativeCases(string set, string subset)
         {
             // Arrange