.NET 7迁移WCF客户端时CreateMessage因转义ASCII字符失败

问题背景 #

将WCF客户端从.NET Framework迁移到.NET 7后，序列化包含ASCII 0x07分隔符的对象时，原本在.NET Framework中该字符会自动转义为，但在.NET 7中调用Message.ToString()时抛出System.ArgumentException: '\a', hexadecimal value 0x07, is an invalid character异常。直接使用XmlReader/XmlWriter时可通过CheckCharacters = false跳过检查，但WCF Message对象没有直接配置该属性的入口。

解决方案 #

方案1：自定义客户端消息格式化器（推荐） #

通过实现IClientMessageFormatter扩展WCF的序列化逻辑，手动配置XmlWriter关闭字符检查：

public class CustomClientFormatter : IClientMessageFormatter
{
    private readonly IClientMessageFormatter _originalFormatter;

    public CustomClientFormatter(IClientMessageFormatter originalFormatter)
    {
        _originalFormatter = originalFormatter;
    }

    public Message SerializeRequest(MessageVersion messageVersion, object[] parameters)
    {
        var originalMessage = _originalFormatter.SerializeRequest(messageVersion, parameters);
        var bufferedCopy = originalMessage.CreateBufferedCopy(int.MaxValue);
        var clonedMessage = bufferedCopy.CreateMessage();

        // 创建新消息，使用关闭字符检查的XmlWriter写入内容
        var newMessage = Message.CreateMessage(messageVersion, clonedMessage.Headers.Action);
        var writerSettings = new XmlWriterSettings { CheckCharacters = false };
        using (var writer = XmlWriter.Create(newMessage.BodyWriter.CreateBufferedCopy(int.MaxValue).CreateReader().ReadSubtree(), writerSettings))
        {
            clonedMessage.WriteBodyContents(writer);
        }

        // 复制原消息的头部和属性
        foreach (var header in clonedMessage.Headers)
        {
            newMessage.Headers.Add(header);
        }
        foreach (var prop in clonedMessage.Properties)
        {
            newMessage.Properties[prop.Key] = prop.Value;
        }

        return newMessage;
    }

    public object[] DeserializeReply(Message message, object[] parameters)
    {
        return _originalFormatter.DeserializeReply(message, parameters);
    }
}

再通过端点行为注入自定义格式化器：

public class CustomFormatterBehavior : IEndpointBehavior
{
    public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters) { }

    public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
    {
        foreach (var operation in clientRuntime.ClientOperations)
        {
            operation.Formatter = new CustomClientFormatter(operation.Formatter);
        }
    }

    public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher) { }

    public void Validate(ServiceEndpoint endpoint) { }
}

最后在客户端实例中添加该行为：

var client = new MyServiceClient();
client.Endpoint.Behaviors.Add(new CustomFormatterBehavior());

方案2：预转义0x07字符 #

在构造Request对象时，手动将0x07替换为XML实体，从源头上避免触发字符检查：

// 假设Request类的SerializedData字段包含分隔符
request.SerializedData = request.SerializedData.Replace("\a", "");

Message wcfMessage = Message.CreateMessage(MessageVersion.Soap12WSAddressing10, "MyServiceAction", request);
var wcfMessageXml = wcfMessage.ToString();

注意：需确认服务端能正确解析预转义的实体，避免兼容性问题。

方案3：反射修改内部XmlWriterSettings（临时 workaround） #

通过反射修改WCF Message内部使用的XmlWriterSettings，强制关闭字符检查：

var request = new Request(...);
Message wcfMessage = Message.CreateMessage(MessageVersion.Soap12WSAddressing10, "MyServiceAction", request);

// 反射获取并修改内部设置
var bodyWriterProp = typeof(Message).GetProperty("BodyWriter", BindingFlags.Instance | BindingFlags.NonPublic);
var bodyWriter = bodyWriterProp?.GetValue(wcfMessage);
var settingsField = bodyWriter?.GetType().GetField("_xmlWriterSettings", BindingFlags.Instance | BindingFlags.NonPublic);
if (settingsField != null)
{
    var settings = (XmlWriterSettings)settingsField.GetValue(bodyWriter);
    settings.CheckCharacters = false;
}

var wcfMessageXml = wcfMessage.ToString();

注意：此方法依赖.NET WCF的内部实现，后续版本可能失效，仅作为临时应急方案。

总结 #

优先选择方案1，这是符合WCF扩展规范的方式，兼容性和可维护性最好；若对象结构简单，方案2是最轻便的选择；方案3仅建议在紧急场景下临时使用。

内容的提问来源于stack exchange，提问作者Andy W