Add PropertyNamingSource enum to support proto field names

README.md

@@ -44,7 +44,26 @@ var deserialized = JsonSerializer.Deserialize<SimpleMessage>(payload, jsonSerial
 ## Configuration
 The library offers several configuration options to fine-tune protobuf serialization. You can modify the default settings using a delegate passed to the AddProtobufSupport method. The available options are described below:
 
-### UseProtobufJsonNames
+### PropertyNamingSource
+This option specifies the source for property names in JSON serialization. The default value is `PropertyNamingSource.Default`.
+
+Available values:
+- `PropertyNamingSource.Default`: Use the default `PropertyNamingPolicy` from `JsonSerializerOptions`.
+- `PropertyNamingSource.ProtobufJsonName`: Use the JsonName from the protobuf contract. This is usually the lower-camel-cased form of the field name, but can be overridden using the `json_name` option in the .proto file.
+- `PropertyNamingSource.ProtobufFieldName`: Use the original field name as defined in the .proto file (e.g., "double_property" instead of "doubleProperty").
+
+Example:
+```csharp
+var jsonSerializerOptions = new JsonSerializerOptions();
+jsonSerializerOptions.AddProtobufSupport(options => 
+{
+    options.PropertyNamingSource = PropertyNamingSource.ProtobufFieldName;
+});
+```
+
+### UseProtobufJsonNames (Obsolete)
+**Note:** This property is obsolete and will be removed in a future version. Use `PropertyNamingSource` instead.
+
 This option defines how property names should be resolved for protobuf contracts. When set to `true`, the `PropertyNamingPolicy` will be ignored, and property names will be derived from the protobuf contract. The default value is `false`.
 
 ### TreatDurationAsTimeSpan

src/Protobuf.System.Text.Json/JsonProtobufSerializerOptions.cs

@@ -12,7 +12,18 @@ public class JsonProtobufSerializerOptions
     /// option in the .proto file.
     /// The default value is false.
     /// </summary>
-    public bool UseProtobufJsonNames { get; set; }
+    [Obsolete("Use PropertyNamingSource instead. This property will be removed in a future version.")]
+    public bool UseProtobufJsonNames
+    {
+        get => PropertyNamingSource == PropertyNamingSource.ProtobufJsonName;
+        set => PropertyNamingSource = value ? PropertyNamingSource.ProtobufJsonName : PropertyNamingSource.Default;
+    }
+
+    /// <summary>
+    /// Specifies the source for property names in JSON serialization.
+    /// The default value is <see cref="PropertyNamingSource.Default"/>.
+    /// </summary>
+    public PropertyNamingSource PropertyNamingSource { get; set; } = PropertyNamingSource.Default;
 
     /// <summary>
     /// Controls how <see cref="Google.Protobuf.WellKnownTypes.Duration"/> fields are handled.

src/Protobuf.System.Text.Json/PropertyNamingSource.cs

@@ -0,0 +1,25 @@
+namespace Protobuf.System.Text.Json;
+
+/// <summary>
+/// Specifies the source for property names in JSON serialization.
+/// </summary>
+public enum PropertyNamingSource
+{
+    /// <summary>
+    /// Use the default PropertyNamingPolicy from JsonSerializerOptions.
+    /// </summary>
+    Default = 0,
+
+    /// <summary>
+    /// Use the JsonName from the protobuf contract.
+    /// This is usually the lower-camel-cased form of the field name,
+    /// but can be overridden using the json_name option in the .proto file.
+    /// </summary>
+    ProtobufJsonName = 1,
+
+    /// <summary>
+    /// Use the original field name as defined in the .proto file.
+    /// For example, "double_property" instead of "doubleProperty".
+    /// </summary>
+    ProtobufFieldName = 2
+}

src/Protobuf.System.Text.Json/ProtobufConverter.cs

@@ -24,7 +24,7 @@ public ProtobufConverter(JsonSerializerOptions jsonSerializerOptions, JsonProtob
         var propertyInfo = type.GetProperty("Descriptor", BindingFlags.Public | BindingFlags.Static);
         var messageDescriptor = (MessageDescriptor) propertyInfo?.GetValue(null, null)!;
 
-        var convertNameFunc = GetConvertNameFunc(jsonSerializerOptions.PropertyNamingPolicy, jsonProtobufSerializerOptions.UseProtobufJsonNames);
+        var convertNameFunc = GetConvertNameFunc(jsonSerializerOptions.PropertyNamingPolicy, jsonProtobufSerializerOptions.PropertyNamingSource);
 
         _fields = messageDescriptor.Fields.InDeclarationOrder().Select(fieldDescriptor =>
         {
@@ -49,19 +49,24 @@ public ProtobufConverter(JsonSerializerOptions jsonSerializerOptions, JsonProtob
         _fieldsLookup = _fields.ToDictionary(x => x.JsonName, x => x, stringComparer);
     }
 
-    private static Func<FieldDescriptor, string> GetConvertNameFunc(JsonNamingPolicy? jsonNamingPolicy, bool useProtobufJsonNames)
+    private static Func<FieldDescriptor, string> GetConvertNameFunc(JsonNamingPolicy? jsonNamingPolicy, PropertyNamingSource propertyNamingSource)
     {
-        if (useProtobufJsonNames)
+        switch (propertyNamingSource)
         {
-            return descriptor => descriptor.JsonName;
-        }
-
-        if (jsonNamingPolicy != null)
-        {
-            return descriptor => jsonNamingPolicy.ConvertName(descriptor.PropertyName);
+            case PropertyNamingSource.ProtobufJsonName:
+                return descriptor => descriptor.JsonName;
+
+            case PropertyNamingSource.ProtobufFieldName:
+                return descriptor => descriptor.Name;
+
+            case PropertyNamingSource.Default:
+            default:
+                if (jsonNamingPolicy != null)
+                {
+                    return descriptor => jsonNamingPolicy.ConvertName(descriptor.PropertyName);
+                }
+                return descriptor => descriptor.PropertyName;
         }
-
-        return descriptor => descriptor.PropertyName;
     }
 
     public override T? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)

test/Protobuf.System.Text.Json.Tests/JsonNamingPolicyTests.Should_use_protobuf_field_name_when_PropertyNamingSource_set_to_ProtobufFieldName.approved.json

@@ -0,0 +1,17 @@
+{
+  "double_property": 2.5,
+  "float_property": 0,
+  "int_32_property": 0,
+  "int_64_property": 0,
+  "uint_32_property": 0,
+  "uint_64_property": 0,
+  "sint_32_property": 0,
+  "sint_64_property": 0,
+  "fixed_32_property": 0,
+  "fixed_64_property": 0,
+  "sfixed_32_property": 0,
+  "sfixed_64_property": 0,
+  "bool_property": false,
+  "string_property": "",
+  "bytes_property": ""
+}

test/Protobuf.System.Text.Json.Tests/JsonNamingPolicyTests.Should_use_protobuf_json_name_when_PropertyNamingSource_set_to_ProtobufJsonName.approved.json

@@ -0,0 +1,17 @@
+{
+  "doubleProperty": 2.5,
+  "floatProperty": 0,
+  "int32Property": 0,
+  "int64Property": 0,
+  "uint32Property": 0,
+  "uint64Property": 0,
+  "sint32Property": 0,
+  "sint64Property": 0,
+  "fixed32Property": 0,
+  "fixed64Property": 0,
+  "sfixed32Property": 0,
+  "sfixed64Property": 0,
+  "boolProperty": false,
+  "stringProperty": "",
+  "bytesProperty": ""
+}

test/Protobuf.System.Text.Json.Tests/JsonNamingPolicyTests.cs

@@ -37,7 +37,9 @@ public void Should_ignore_PropertyNamingPolicy_when_UseProtobufJsonNames_set_to_
         };
         var jsonSerializerOptions = new JsonSerializerOptions();
         jsonSerializerOptions.PropertyNamingPolicy = new JsonLowerCaseNamingPolicy();
+#pragma warning disable CS0618 // Type or member is obsolete
         jsonSerializerOptions.AddProtobufSupport(options => options.UseProtobufJsonNames = true);
+#pragma warning restore CS0618 // Type or member is obsolete
 
         // Act
         var serialized = JsonSerializer.Serialize(msg, jsonSerializerOptions);
@@ -47,6 +49,62 @@ public void Should_ignore_PropertyNamingPolicy_when_UseProtobufJsonNames_set_to_
         approver.VerifyJson(serialized);
     }
 
+    [Fact]
+    public void Should_use_protobuf_json_name_when_PropertyNamingSource_set_to_ProtobufJsonName()
+    {
+        // Arrange
+        var msg = new SimpleMessage
+        {
+            DoubleProperty = 2.5d
+        };
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.PropertyNamingPolicy = new JsonLowerCaseNamingPolicy();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufJsonName);
+
+        // Act
+        var serialized = JsonSerializer.Serialize(msg, jsonSerializerOptions);
+
+        // Assert
+        var approver = new ExplicitApprover();
+        approver.VerifyJson(serialized);
+    }
+
+    [Fact]
+    public void Should_use_protobuf_field_name_when_PropertyNamingSource_set_to_ProtobufFieldName()
+    {
+        // Arrange
+        var msg = new SimpleMessage
+        {
+            DoubleProperty = 2.5d
+        };
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.PropertyNamingPolicy = new JsonLowerCaseNamingPolicy();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufFieldName);
+
+        // Act
+        var serialized = JsonSerializer.Serialize(msg, jsonSerializerOptions);
+
+        // Assert
+        var approver = new ExplicitApprover();
+        approver.VerifyJson(serialized);
+    }
+
+    [Fact]
+    public void Should_deserialize_using_protobuf_field_name_when_PropertyNamingSource_set_to_ProtobufFieldName()
+    {
+        // Arrange
+        var json = "{\"double_property\": 2.5}";
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufFieldName);
+
+        // Act
+        var deserialized = JsonSerializer.Deserialize<SimpleMessage>(json, jsonSerializerOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(2.5d, deserialized.DoubleProperty);
+    }
+
     private class JsonLowerCaseNamingPolicy : JsonNamingPolicy
     {
         public override string ConvertName(string name)

test/Protobuf.System.Text.Json.Tests/PropertyNamingSourceTests.Should_use_custom_json_name_when_PropertyNamingSource_is_ProtobufJsonName.approved.json

@@ -0,0 +1,4 @@
+{
+  "customDoubleProperty": 2.5,
+  "stringProperty": "test"
+}

test/Protobuf.System.Text.Json.Tests/PropertyNamingSourceTests.Should_use_proto_field_name_when_PropertyNamingSource_is_ProtobufFieldName.approved.json

@@ -0,0 +1,4 @@
+{
+  "double_property": 2.5,
+  "string_property": "test"
+}

test/Protobuf.System.Text.Json.Tests/PropertyNamingSourceTests.cs

@@ -0,0 +1,105 @@
+using System.Text.Json;
+using System.Text.Json.Protobuf.Tests;
+using SmartAnalyzers.ApprovalTestsExtensions;
+using Xunit;
+
+namespace Protobuf.System.Text.Json.Tests;
+
+public class PropertyNamingSourceTests
+{
+    [Fact]
+    public void Should_use_custom_json_name_when_PropertyNamingSource_is_ProtobufJsonName()
+    {
+        // Arrange
+        var msg = new MessageWithCustomJsonName
+        {
+            DoubleProperty = 2.5d,
+            StringProperty = "test"
+        };
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufJsonName);
+
+        // Act
+        var serialized = JsonSerializer.Serialize(msg, jsonSerializerOptions);
+
+        // Assert
+        var approver = new ExplicitApprover();
+        approver.VerifyJson(serialized);
+    }
+
+    [Fact]
+    public void Should_use_proto_field_name_when_PropertyNamingSource_is_ProtobufFieldName()
+    {
+        // Arrange
+        var msg = new MessageWithCustomJsonName
+        {
+            DoubleProperty = 2.5d,
+            StringProperty = "test"
+        };
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufFieldName);
+
+        // Act
+        var serialized = JsonSerializer.Serialize(msg, jsonSerializerOptions);
+
+        // Assert
+        var approver = new ExplicitApprover();
+        approver.VerifyJson(serialized);
+    }
+
+    [Fact]
+    public void Should_deserialize_using_custom_json_name_when_PropertyNamingSource_is_ProtobufJsonName()
+    {
+        // Arrange
+        var json = "{\"customDoubleProperty\": 2.5, \"stringProperty\": \"test\"}";
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufJsonName);
+
+        // Act
+        var deserialized = JsonSerializer.Deserialize<MessageWithCustomJsonName>(json, jsonSerializerOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(2.5d, deserialized.DoubleProperty);
+        Assert.Equal("test", deserialized.StringProperty);
+    }
+
+    [Fact]
+    public void Should_deserialize_using_proto_field_name_when_PropertyNamingSource_is_ProtobufFieldName()
+    {
+        // Arrange
+        var json = "{\"double_property\": 2.5, \"string_property\": \"test\"}";
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufFieldName);
+
+        // Act
+        var deserialized = JsonSerializer.Deserialize<MessageWithCustomJsonName>(json, jsonSerializerOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(2.5d, deserialized.DoubleProperty);
+        Assert.Equal("test", deserialized.StringProperty);
+    }
+
+    [Fact]
+    public void Should_round_trip_with_ProtobufFieldName()
+    {
+        // Arrange
+        var original = new MessageWithCustomJsonName
+        {
+            DoubleProperty = 2.5d,
+            StringProperty = "test"
+        };
+        var jsonSerializerOptions = new JsonSerializerOptions();
+        jsonSerializerOptions.AddProtobufSupport(options => options.PropertyNamingSource = PropertyNamingSource.ProtobufFieldName);
+
+        // Act
+        var serialized = JsonSerializer.Serialize(original, jsonSerializerOptions);
+        var deserialized = JsonSerializer.Deserialize<MessageWithCustomJsonName>(serialized, jsonSerializerOptions);
+
+        // Assert
+        Assert.NotNull(deserialized);
+        Assert.Equal(original.DoubleProperty, deserialized.DoubleProperty);
+        Assert.Equal(original.StringProperty, deserialized.StringProperty);
+    }
+}

test/Protobuf.System.Text.Json.Tests/Protos/message_with_custom_json_name.proto

@@ -0,0 +1,9 @@
+syntax = "proto3";
+
+option csharp_namespace = "System.Text.Json.Protobuf.Tests";
+
+message MessageWithCustomJsonName {
+  double double_property = 1 [json_name = "customDoubleProperty"];
+
+  string string_property = 2;
+}