c# - XML 文档 (1, 1) 中存在错误。反序列化一个简单的 xml 字符串时

Question

我检查了this post之前，但它对我没有帮助(它也没有被接受的答案)。

这个测试失败了:

using System.IO;
using System.Xml.Serialization;
using Xunit;

namespace ATest
{
    public class XmlSerializerTest
    {
        [Fact]
        public void DeserializeTest()
        {
            string request = Serializer.ByteArrayToString(new RegisterRequest{ ... }
               .ToXml());

            RegisterRequest deserialized = request.DeserializeXmlString<RegisterRequest>();

            Assert.NotNull(deserialized);
        }
    }

    public static class Serializer
    {
        public static T DeserializeXmlString<T>(this string xmlObj)
        {
            T outputObject;
            using (StringReader xmlReader = new StringReader(xmlObj))
            {
                var serializer = new XmlSerializer(typeof(T));
                outputObject = (T)serializer.Deserialize(xmlReader); // throws here
            }
            return outputObject;
        }

        public static byte[] ToXml<T>(this T obj)
        {
            XmlWriterSettings settings = new XmlWriterSettings();
            settings.Encoding = Encoding.UTF8;
            settings.Indent = false;

            using MemoryStream ms = new MemoryStream();
            using XmlWriter xmlWriter = XmlWriter.Create(ms, settings);

            XmlSerializerNamespaces namespaces = new XmlSerializerNamespaces();
            namespaces.Add(String.Empty, String.Empty);

            XmlSerializer serializer = new XmlSerializer(typeof(T));
            serializer.Serialize(xmlWriter, obj, namespaces);

            return ms.ToArray();
        }

        // And convert that byte[] to string with this:
        public static string ByteArrayToString(byte[] bytes) =>
                Encoding.UTF8.GetString(bytes);
    }

    [XmlRoot(elementName: "RegisterRequest")]
    public class RegisterRequest
    {
        [XmlElement]
        public int WorkerId;

        [XmlElement]
        public string WorkerIP;

        [XmlElement]
        public int WorkerPort;
    }
}

我得到的错误是:

System.InvalidOperationException: 'There is an error in XML document (1, 1).'

InnerExceptionXmlException: Data at the root level is invalid. Line 1, position 1.

Answer 1

这里的问题是 Encoding.UTF8 是带有 BOM(字节顺序标记)的 UTF-8 编码，这意味着 XmlSerializer 在开头发出几个字节以指示所述字节顺序标记。因此，您的 ToXml 的结果在开头包含那些非字符字节，并且反序列化失败，因为反序列化不需要它们。要修复，请通过执行以下操作告诉序列化程序不要发出 BOM:

XmlWriterSettings settings = new XmlWriterSettings();
//settings.Encoding = Encoding.UTF8;
settings.Encoding = new UTF8Encoding(false); // false means no BOM here

顺便说一句，您粘贴到问题中的文本不包含所述不可见字符，因此使用您粘贴的特定硬编码字符串无法重现问题。但是，由于您包含了产生问题字符串的代码 - 可以通过手动调用 ByteArrayToString(ToXml(..)) 来重现它。