如何用protobuf-net序列化时兼容proto3包装类型字段格式？

问题概述 #

与协作方基于proto3协议对接，对方定义的RemoteDOutCommand消息中使用了google.protobuf.UInt32Value、BoolValue等包装类型。但在.NET 6中用protobuf-net（v3.22.0）将uint?/bool?类型的字段序列化后，生成的字节流不符合proto3包装类型的嵌套结构，导致protoc解码时显示为直接数值而非预期的包装类型结构。

对方的proto3核心定义：

syntax = "proto3";
import "google/protobuf/wrappers.proto";
package RemoteDOutCommandConfig;

message RemoteDOutCommand
{
    google.protobuf.UInt32Value command_id = 1; //transaction ID
    google.protobuf.BoolValue command_value = 2;
    uint32 command_trigger_time_utc = 3;
    google.protobuf.UInt32Value acceptable_execution_latency_secs = 4;
    google.protobuf.BoolValue disable_latency_check = 5;
}

原.NET类定义（存在问题）：

public partial class RemoteDOutCommand
{
    [global::ProtoBuf.ProtoMember(1, Name = @"command_id")]
    public uint? CommandId { get; set; }

    [global::ProtoBuf.ProtoMember(2, Name = @"command_value")]
    public bool? CommandValue { get; set; }

    [global::ProtoBuf.ProtoMember(3, Name = @"command_trigger_time_utc")]
    public uint CommandTriggerTimeUtc { get; set; }

    [global::ProtoBuf.ProtoMember(4, Name = @"acceptable_execution_latency_secs")]
    public uint? AcceptableExecutionLatencySecs { get; set; }

    [global::ProtoBuf.ProtoMember(5, Name = @"disable_latency_check")]
    public bool? DisableLatencyCheck { get; set; }
}

解决方案 #

protobuf-net默认会把nullable值类型序列化为proto3的普通可选字段，而非Google包装类型的嵌套结构。要匹配对方的格式，需让字段对应到包装类型的结构，有两种可行方式：

方式1：使用官方Google.Protobuf包装类型（推荐） #

1. 安装NuGet包Google.Protobuf，该包包含官方定义的UInt32Value、BoolValue等包装类型。
2. 修改.NET类，将nullable值类型替换为对应的Google包装类型：

public partial class RemoteDOutCommand
{
    [global::ProtoBuf.ProtoMember(1, Name = @"command_id")]
    public Google.Protobuf.WellKnownTypes.UInt32Value CommandId { get; set; }

    [global::ProtoBuf.ProtoMember(2, Name = @"command_value")]
    public Google.Protobuf.WellKnownTypes.BoolValue CommandValue { get; set; }

    [global::ProtoBuf.ProtoMember(3, Name = @"command_trigger_time_utc")]
    public uint CommandTriggerTimeUtc { get; set; }

    [global::ProtoBuf.ProtoMember(4, Name = @"acceptable_execution_latency_secs")]
    public Google.Protobuf.WellKnownTypes.UInt32Value AcceptableExecutionLatencySecs { get; set; }

    [global::ProtoBuf.ProtoMember(5, Name = @"disable_latency_check")]
    public Google.Protobuf.WellKnownTypes.BoolValue DisableLatencyCheck { get; set; }
}

这样protobuf-net会自动按照proto3包装类型的嵌套结构序列化，生成的字节流与对方示例完全匹配。

方式2：自定义包装类并配置protobuf-net属性 #

若不想依赖Google.Protobuf包，可手动定义与proto包装类型结构一致的类：

// 自定义UInt32Value包装类，匹配proto定义
[global::ProtoBuf.ProtoContract(Name = @"UInt32Value")]
public class UInt32Value
{
    [global::ProtoBuf.ProtoMember(1, Name = @"value")]
    public uint Value { get; set; }
}

// 自定义BoolValue包装类，匹配proto定义
[global::ProtoBuf.ProtoContract(Name = @"BoolValue")]
public class BoolValue
{
    [global::ProtoBuf.ProtoMember(1, Name = @"value")]
    public bool Value { get; set; }
}

// 修改RemoteDOutCommand类
public partial class RemoteDOutCommand
{
    [global::ProtoBuf.ProtoMember(1, Name = @"command_id")]
    public UInt32Value CommandId { get; set; }

    [global::ProtoBuf.ProtoMember(2, Name = @"command_value")]
    public BoolValue CommandValue { get; set; }

    [global::ProtoBuf.ProtoMember(3, Name = @"command_trigger_time_utc")]
    public uint CommandTriggerTimeUtc { get; set; }

    [global::ProtoBuf.ProtoMember(4, Name = @"acceptable_execution_latency_secs")]
    public UInt32Value AcceptableExecutionLatencySecs { get; set; }

    [global::ProtoBuf.ProtoMember(5, Name = @"disable_latency_check")]
    public BoolValue DisableLatencyCheck { get; set; }
}

需确保自定义类的ProtoContract名称、ProtoMember的编号和名称与proto定义完全一致。

验证效果 #

修改后重新序列化，使用protoc解码将得到与对方示例一致的输出：

command_id {
  value: 12
}
command_value {
}
command_trigger_time_utc: 1675325420
acceptable_execution_latency_secs {
  value: 200
}
disable_latency_check {
  value: true
}

内容的提问来源于stack exchange，提问作者fishberg5051