Add recursion limit handling to JSON parsing.

Fixes issue #932.

csharp/src/Google.Protobuf.Test/CodedInputStreamTest.cs

@@ -284,7 +284,7 @@ namespace Google.Protobuf
             Assert.Throws<InvalidProtocolBufferException>(() => input.ReadBytes());
         }
 
-        private static TestRecursiveMessage MakeRecursiveMessage(int depth)
+        internal static TestRecursiveMessage MakeRecursiveMessage(int depth)
         {
             if (depth == 0)
             {
@@ -296,7 +296,7 @@ namespace Google.Protobuf
             }
         }
 
-        private static void AssertMessageDepth(TestRecursiveMessage message, int depth)
+        internal static void AssertMessageDepth(TestRecursiveMessage message, int depth)
         {
             if (depth == 0)
             {

csharp/src/Google.Protobuf.Test/JsonParserTest.cs

@@ -723,5 +723,23 @@ namespace Google.Protobuf
             string json = "{} 10";
             Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
         }
+
+        /// <summary>
+        /// JSON equivalent to <see cref="CodedInputStreamTest.MaliciousRecursion"/>
+        /// </summary>
+        [Test]
+        public void MaliciousRecursion()
+        {
+            string data64 = CodedInputStreamTest.MakeRecursiveMessage(64).ToString();
+            string data65 = CodedInputStreamTest.MakeRecursiveMessage(65).ToString();
+
+            var parser64 = new JsonParser(new JsonParser.Settings(64));
+            CodedInputStreamTest.AssertMessageDepth(parser64.Parse<TestRecursiveMessage>(data64), 64);
+            Assert.Throws<InvalidProtocolBufferException>(() => parser64.Parse<TestRecursiveMessage>(data65));
+
+            var parser63 = new JsonParser(new JsonParser.Settings(63));
+            Assert.Throws<InvalidProtocolBufferException>(() => parser63.Parse<TestRecursiveMessage>(data64));
+
+        }
     }
 }