从 asp.net POST 方法返回 JSON 时出现“无法翻译 Unicode 字符 \\uD83C”错误

Question

我在 MVC 项目中开发了一个 web api。我在我的 post 方法中返回一个 JToken 对象。通常我的 api 可以正常工作，但有时在特定数据中我会收到此错误：

  "Message": "An error has occurred.",
  "ExceptionMessage": "The 'ObjectContent`1' type failed to serialize the response body for content type 'application/json; charset=utf-8'.",
  "ExceptionType": "System.InvalidOperationException",
  "StackTrace": null,
  "InnerException": {
  "Message": "An error has occurred.",
  "ExceptionMessage": "Unable to translate Unicode character \\uD83C 
   at index 411 to specified code page."

这是我的发帖方式

public JToken Post([FromBody]Classes.Search search)
    {

        Classes.ReturnSearch returnSearch = new Classes.ReturnSearch();
        try
        {
            string con = System.Configuration.ConfigurationManager.ConnectionStrings["TConnectionString"].ConnectionString;
            SqlConnection cn = new SqlConnection(con);
            SqlDataAdapter sqlDataAdapter = new SqlDataAdapter("SP_Searchi", cn);
            sqlDataAdapter.SelectCommand.CommandType = CommandType.StoredProcedure;
            sqlDataAdapter.SelectCommand.Parameters.Add(new SqlParameter("@word", search.word));

            sqlDataAdapter.SelectCommand.Parameters.Add(new SqlParameter("@num", search.num));
            DataSet d = new DataSet();
            sqlDataAdapter.Fill(d);
            DataTable table = d.Tables[0];

            foreach(DataRow row in table.Rows)
            {
                string result=row[1].ToString();

                returnSearch.search_items.Add(new Classes.SearchItem(row[0].ToString(), row[1].ToString(),search.word));
            }
            returnSearch.status = "Success";


            return JObject.Parse(JsonConvert.SerializeObject(returnSearch));
        }
        catch (Exception e)
        {
            returnSearch.status = "Failed";
            returnSearch.search_items = null;
            ValuesController.Log("Error in Search: "+e.Message);
            return JObject.Parse(JsonConvert.SerializeObject(returnSearch));
        }


    }

有什么问题？！

Answer 1

这是一个表情符号修饰符。您可能会在解析输入的表情符号后看到它（可以拆分为多个 \u#### 实例）。

Answer 2

您的问题是 U+D83C is not a valid unicode character 以某种方式进入了您的 returnSearch 对象内的字符串之一。随后，asp.net-mvc 框架抛出异常，试图将这样的字符编码为 utf-8。

您需要做的是确定此角色如何进入您的returnSearch 结果并解决该潜在问题。由于您已经手动将返回的结果转换为JObject，为了使调试更容易，您可以使用以下转换器将所有字符串测试编码为 utf-8 并在出现问题时抛出异常：

public class EncodingValidatingStringConverter : JsonConverter
{
    readonly Encoding encoding;

    public EncodingValidatingStringConverter()
        : this(Encoding.GetEncoding(Encoding.UTF8.CodePage, new EncoderReplacementFallback("?"), new DecoderExceptionFallback()))
    {
    }

    public EncodingValidatingStringConverter(Encoding encoding)
    {
        if (encoding == null)
            throw new ArgumentNullException();
        this.encoding = encoding;
    }

    public override bool CanConvert(Type objectType)
    {
        return objectType == typeof(string);
    }

    public override bool CanRead { get { return false; } }

    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }

    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
    {
        var s = (string)value;
        var bytes = encoding.GetBytes(s);
        var sFixed = encoding.GetString(bytes);

        writer.WriteValue(sFixed);
    }
}

然后修改您的Post() 方法以捕获并记录EncoderFallbackException 并按照似乎可取的方式处理问题。例如，以下版本的方法在记录后将无效字符替换为 ? 字符：

        try
        {
            // Fill in the returnSearch

            // Convert to JObject and return
            var settings = new JsonSerializerSettings
            {
                Converters = new[] { new EncodingValidatingStringConverter(Encoding.GetEncoding(Encoding.UTF8.CodePage, new EncoderExceptionFallback(), new DecoderExceptionFallback())) },
            };
            return JObject.FromObject(returnSearch, JsonSerializer.CreateDefault(settings));
        }
        catch (EncoderFallbackException ex)
        {
            // Log the encoding error for debugging:
            ValuesController.Log("Encoding exception:\n" + ex.ToString());
            // You could log the search parameters or entire search_items list as well if desired.

            // Return whatever seems most advisable, e.g. replacing the bad character with a fallback if preferred.
            var settings = new JsonSerializerSettings
            {
                Converters = new[] { new EncodingValidatingStringConverter(Encoding.GetEncoding(Encoding.UTF8.CodePage, new EncoderReplacementFallback("?"), new DecoderExceptionFallback())) },
            };
            return JObject.FromObject(returnSearch, JsonSerializer.CreateDefault(settings));
        }
        catch (Exception ex)
        {
            returnSearch.status = "Failed";
            returnSearch.search_items = null;
            ValuesController.Log("Error in Search: " + ex.Message);
            var settings = new JsonSerializerSettings
            {
                Converters = new[] { new EncodingValidatingStringConverter(Encoding.GetEncoding(Encoding.UTF8.CodePage, new EncoderReplacementFallback("?"), new DecoderExceptionFallback())) },
            };
            return JObject.FromObject(returnSearch, JsonSerializer.CreateDefault(settings));
        }

请注意，对每个字符串进行测试编码会对性能产生负面影响，因此一旦您解决了根本问题，您应该删除此解决方法。

顺便说一句，您可以使用JObject.FromObject(returnSearch) 而不是JObject.Parse(JsonConvert.SerializeObject(returnSearch))。此方法直接写入JToken 层次结构，无需中间字符串表示，因此应该具有更好的性能。