Increase C# default recursion limit to 100 (#5339)

* Increase C# default recursion limit to 100

This matches the Java and C++ defaults.

* Change compatibility tests to use execution-time default recursion limit

This way the same tests should pass against all versions, even
if the recursion limit changes. (The tests will be testing whether
different messages work, admittedly - but that's probably fine.)

csharp/compatibility_tests/v3.0.0/src/Google.Protobuf.Test/CodedInputStreamTest.cs

@@ -313,14 +313,14 @@ namespace Google.Protobuf
         [Test]
         public void MaliciousRecursion()
         {
-            ByteString data64 = MakeRecursiveMessage(64).ToByteString();
-            ByteString data65 = MakeRecursiveMessage(65).ToByteString();
+            ByteString atRecursiveLimit = MakeRecursiveMessage(CodedInputStream.DefaultRecursionLimit).ToByteString();
+            ByteString beyondRecursiveLimit = MakeRecursiveMessage(CodedInputStream.DefaultRecursionLimit + 1).ToByteString();
 
-            AssertMessageDepth(TestRecursiveMessage.Parser.ParseFrom(data64), 64);
+            AssertMessageDepth(TestRecursiveMessage.Parser.ParseFrom(atRecursiveLimit), CodedInputStream.DefaultRecursionLimit);
 
-            Assert.Throws<InvalidProtocolBufferException>(() => TestRecursiveMessage.Parser.ParseFrom(data65));
+            Assert.Throws<InvalidProtocolBufferException>(() => TestRecursiveMessage.Parser.ParseFrom(beyondRecursiveLimit));
 
-            CodedInputStream input = CodedInputStream.CreateWithLimits(new MemoryStream(data64.ToByteArray()), 1000000, 63);
+            CodedInputStream input = CodedInputStream.CreateWithLimits(new MemoryStream(atRecursiveLimit.ToByteArray()), 1000000, CodedInputStream.DefaultRecursionLimit - 1);
             Assert.Throws<InvalidProtocolBufferException>(() => TestRecursiveMessage.Parser.ParseFrom(input));
         }
 

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

@@ -327,14 +327,14 @@ namespace Google.Protobuf
         [Test]
         public void MaliciousRecursion()
         {
-            ByteString data64 = MakeRecursiveMessage(64).ToByteString();
-            ByteString data65 = MakeRecursiveMessage(65).ToByteString();
+            ByteString atRecursiveLimit = MakeRecursiveMessage(CodedInputStream.DefaultRecursionLimit).ToByteString();
+            ByteString beyondRecursiveLimit = MakeRecursiveMessage(CodedInputStream.DefaultRecursionLimit + 1).ToByteString();
 
-            AssertMessageDepth(TestRecursiveMessage.Parser.ParseFrom(data64), 64);
+            AssertMessageDepth(TestRecursiveMessage.Parser.ParseFrom(atRecursiveLimit), CodedInputStream.DefaultRecursionLimit);
 
-            Assert.Throws<InvalidProtocolBufferException>(() => TestRecursiveMessage.Parser.ParseFrom(data65));
+            Assert.Throws<InvalidProtocolBufferException>(() => TestRecursiveMessage.Parser.ParseFrom(beyondRecursiveLimit));
 
-            CodedInputStream input = CodedInputStream.CreateWithLimits(new MemoryStream(data64.ToByteArray()), 1000000, 63);
+            CodedInputStream input = CodedInputStream.CreateWithLimits(new MemoryStream(atRecursiveLimit.ToByteArray()), 1000000, CodedInputStream.DefaultRecursionLimit - 1);
             Assert.Throws<InvalidProtocolBufferException>(() => TestRecursiveMessage.Parser.ParseFrom(input));
         }
 

csharp/src/Google.Protobuf/CodedInputStream.cs

@@ -93,7 +93,7 @@ namespace Google.Protobuf
         private uint nextTag = 0;
         private bool hasNextTag = false;
 
-        internal const int DefaultRecursionLimit = 64;
+        internal const int DefaultRecursionLimit = 100;
         internal const int DefaultSizeLimit = Int32.MaxValue;
         internal const int BufferSize = 4096;
 
@@ -260,7 +260,7 @@ namespace Google.Protobuf
         /// to avoid maliciously-recursive data.
         /// </summary>
         /// <remarks>
-        /// The default limit is 64.
+        /// The default limit is 100.
         /// </remarks>
         /// <value>
         /// The recursion limit for this stream.