Handle JSON parsing for Any.

This required a rework of the tokenizer to allow for a "replaying" tokenizer, basically in case the @type value comes after the data itself. This rework is nice in some ways (all the pushback and object depth logic in one place) but is a little fragile in terms of token push-back when using the replay tokenizer. It'll be fine for the scenario we need it for, but we should be careful...

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

@@ -30,6 +30,7 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 
+using Google.Protobuf.Reflection;
 using Google.Protobuf.TestProtos;
 using Google.Protobuf.WellKnownTypes;
 using NUnit.Framework;
@@ -717,6 +718,55 @@ namespace Google.Protobuf
             CollectionAssert.AreEqual(expectedPaths, parsed.Paths);
         }
 
+        [Test]
+        public void Any_RegularMessage()
+        {
+            var registry = TypeRegistry.FromMessages(TestAllTypes.Descriptor);
+            var formatter = new JsonFormatter(new JsonFormatter.Settings(false, TypeRegistry.FromMessages(TestAllTypes.Descriptor)));
+            var message = new TestAllTypes { SingleInt32 = 10, SingleNestedMessage = new TestAllTypes.Types.NestedMessage { Bb = 20 } };
+            var original = Any.Pack(message);
+            var json = formatter.Format(original); // This is tested in JsonFormatterTest
+            var parser = new JsonParser(new JsonParser.Settings(10, registry));
+            Assert.AreEqual(original, parser.Parse<Any>(json));
+            string valueFirstJson = "{ \"singleInt32\": 10, \"singleNestedMessage\": { \"bb\": 20 }, \"@type\": \"type.googleapis.com/protobuf_unittest.TestAllTypes\" }";
+            Assert.AreEqual(original, parser.Parse<Any>(valueFirstJson));
+        }
+
+        [Test]
+        public void Any_UnknownType()
+        {
+            string json = "{ \"@type\": \"type.googleapis.com/bogus\" }";
+            Assert.Throws<InvalidOperationException>(() => Any.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void Any_WellKnownType()
+        {
+            var registry = TypeRegistry.FromMessages(Timestamp.Descriptor);
+            var formatter = new JsonFormatter(new JsonFormatter.Settings(false, registry));
+            var timestamp = new DateTime(1673, 6, 19, 12, 34, 56, DateTimeKind.Utc).ToTimestamp();
+            var original = Any.Pack(timestamp);
+            var json = formatter.Format(original); // This is tested in JsonFormatterTest
+            var parser = new JsonParser(new JsonParser.Settings(10, registry));
+            Assert.AreEqual(original, parser.Parse<Any>(json));
+            string valueFirstJson = "{ \"value\": \"1673-06-19T12:34:56Z\", \"@type\": \"type.googleapis.com/google.protobuf.Timestamp\" }";
+            Assert.AreEqual(original, parser.Parse<Any>(valueFirstJson));
+        }
+
+        [Test]
+        public void Any_Nested()
+        {
+            var registry = TypeRegistry.FromMessages(TestWellKnownTypes.Descriptor, TestAllTypes.Descriptor);
+            var formatter = new JsonFormatter(new JsonFormatter.Settings(false, registry));
+            var parser = new JsonParser(new JsonParser.Settings(10, registry));
+            var doubleNestedMessage = new TestAllTypes { SingleInt32 = 20 };
+            var nestedMessage = Any.Pack(doubleNestedMessage);
+            var message = new TestWellKnownTypes { AnyField = Any.Pack(nestedMessage) };
+            var json = formatter.Format(message);
+            // Use the descriptor-based parser just for a change.
+            Assert.AreEqual(message, parser.Parse(json, TestWellKnownTypes.Descriptor));
+        }
+
         [Test]
         public void DataAfterObject()
         {

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

@@ -85,7 +85,7 @@ namespace Google.Protobuf
         public void ObjectDepth()
         {
             string json = "{ \"foo\": { \"x\": 1, \"y\": [ 0 ] } }";
-            var tokenizer = new JsonTokenizer(new StringReader(json));
+            var tokenizer = JsonTokenizer.FromTextReader(new StringReader(json));
             // If we had more tests like this, I'd introduce a helper method... but for one test, it's not worth it.
             Assert.AreEqual(0, tokenizer.ObjectDepth);
             Assert.AreEqual(JsonToken.StartObject, tokenizer.Next());
@@ -118,7 +118,7 @@ namespace Google.Protobuf
         public void ObjectDepth_WithPushBack()
         {
             string json = "{}";
-            var tokenizer = new JsonTokenizer(new StringReader(json));
+            var tokenizer = JsonTokenizer.FromTextReader(new StringReader(json));
             Assert.AreEqual(0, tokenizer.ObjectDepth);
             var token = tokenizer.Next();
             Assert.AreEqual(1, tokenizer.ObjectDepth);
@@ -275,7 +275,7 @@ namespace Google.Protobuf
             // Note: we don't test that the earlier tokens are exactly as expected,
             // partly because that's hard to parameterize.
             var reader = new StringReader(json.Replace('\'', '"'));
-            var tokenizer = new JsonTokenizer(reader);
+            var tokenizer = JsonTokenizer.FromTextReader(reader);
             for (int i = 0; i < expectedValidTokens; i++)
             {
                 Assert.IsNotNull(tokenizer.Next());
@@ -334,7 +334,7 @@ namespace Google.Protobuf
         [Test]
         public void NextAfterEndDocumentThrows()
         {
-            var tokenizer = new JsonTokenizer(new StringReader("null"));
+            var tokenizer = JsonTokenizer.FromTextReader(new StringReader("null"));
             Assert.AreEqual(JsonToken.Null, tokenizer.Next());
             Assert.AreEqual(JsonToken.EndDocument, tokenizer.Next());
             Assert.Throws<InvalidOperationException>(() => tokenizer.Next());
@@ -343,7 +343,7 @@ namespace Google.Protobuf
         [Test]
         public void CanPushBackEndDocument()
         {
-            var tokenizer = new JsonTokenizer(new StringReader("null"));
+            var tokenizer = JsonTokenizer.FromTextReader(new StringReader("null"));
             Assert.AreEqual(JsonToken.Null, tokenizer.Next());
             Assert.AreEqual(JsonToken.EndDocument, tokenizer.Next());
             tokenizer.PushBack(JsonToken.EndDocument);
@@ -373,7 +373,7 @@ namespace Google.Protobuf
         private static void AssertTokensNoReplacement(string json, params JsonToken[] expectedTokens)
         {
             var reader = new StringReader(json);
-            var tokenizer = new JsonTokenizer(reader);
+            var tokenizer = JsonTokenizer.FromTextReader(reader);
             for (int i = 0; i < expectedTokens.Length; i++)
             {
                 var actualToken = tokenizer.Next();
@@ -393,7 +393,7 @@ namespace Google.Protobuf
         private static void AssertThrowsAfter(string json, params JsonToken[] expectedTokens)
         {
             var reader = new StringReader(json);
-            var tokenizer = new JsonTokenizer(reader);
+            var tokenizer = JsonTokenizer.FromTextReader(reader);
             for (int i = 0; i < expectedTokens.Length; i++)
             {
                 var actualToken = tokenizer.Next();

csharp/src/Google.Protobuf/JsonFormatter.cs

@@ -808,12 +808,17 @@ namespace Google.Protobuf
         /// </summary>
         public sealed class Settings
         {
-            private static readonly Settings defaultInstance = new Settings(false);
-
             /// <summary>
             /// Default settings, as used by <see cref="JsonFormatter.Default"/>
             /// </summary>
-            public static Settings Default { get; } = new Settings(false);
+            public static Settings Default { get; }
+
+            // Workaround for the Mono compiler complaining about XML comments not being on
+            // valid language elements.
+            static Settings()
+            {
+                Default = new Settings(false);
+            }
 
             /// <summary>
             /// Whether fields whose values are the default for the field type (e.g. 0 for integers)