azureservicebus - 为什么 Azure WebJob ServiceBus 默认反序列化 XML？

Question

我有一个简单的 Azure WebJobs ServiceBusTrigger，看起来像

public static async void ProcessQueueMessage([ServiceBusTrigger("myqueuename")] String json, TextWriter log) { ... }

不幸的是，它无法将 JSON 反序列化为 XML(这并不奇怪)。我检查了有效负载并确认它只是一个 UTF-8 编码的字节数组。我有两个问题。

1. 为什么假设我的字符串是 XML？
2. 我如何告诉它不，没有 XML，只有一个字符串？

堆栈跟踪:

System.InvalidOperationException: Exception binding parameter 'json' ---> System.Runtime.Serialization.SerializationException: There was an error deserializing the object of type System.String. The input source is not correctly formatted. ---> System.Xml.XmlException: The input source is not correctly formatted.
 at System.Xml.XmlExceptionHelper.ThrowXmlException(XmlDictionaryReader reader, String res, String arg1, String arg2, String arg3)
 at System.Xml.XmlBufferReader.ReadValue(XmlBinaryNodeType nodeType, ValueHandle value)
 at System.Xml.XmlBinaryReader.ReadNode()
 at System.Xml.XmlBinaryReader.Read()
 at System.Xml.XmlBaseReader.IsStartElement()
 at System.Xml.XmlBaseReader.IsStartElement(XmlDictionaryString localName, XmlDictionaryString namespaceUri)
 at System.Runtime.Serialization.XmlReaderDelegator.IsStartElement(XmlDictionaryString localname, XmlDictionaryString ns)
 at System.Runtime.Serialization.XmlObjectSerializer.IsRootElement(XmlReaderDelegator reader, DataContract contract, XmlDictionaryString name, XmlDictionaryString ns)
 at System.Runtime.Serialization.DataContractSerializer.InternalIsStartObject(XmlReaderDelegator reader)
 at System.Runtime.Serialization.DataContractSerializer.InternalReadObject(XmlReaderDelegator xmlReader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
 at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
 --- End of inner exception stack trace ---
 at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
 at System.Runtime.Serialization.DataContractSerializer.ReadObject(XmlDictionaryReader reader, Boolean verifyObjectName)
 at Microsoft.ServiceBus.Messaging.DataContractBinarySerializer.ReadObject(XmlDictionaryReader reader, Boolean verifyObjectName)
 at System.Runtime.Serialization.XmlObjectSerializer.ReadObject(XmlReader reader, Boolean verifyObjectName)
 at System.Runtime.Serialization.XmlObjectSerializer.InternalReadObject(XmlReaderDelegator reader, Boolean verifyObjectName)
 at System.Runtime.Serialization.XmlObjectSerializer.InternalReadObject(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
 at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
 at System.Runtime.Serialization.XmlObjectSerializer.ReadObject(XmlDictionaryReader reader)
 at Microsoft.ServiceBus.Messaging.DataContractBinarySerializer.ReadObject(Stream stream)
 at Microsoft.ServiceBus.Messaging.BrokeredMessage.GetBody[T](XmlObjectSerializer serializer)
 at Microsoft.ServiceBus.Messaging.BrokeredMessage.GetBody[T]()
 at Microsoft.Azure.WebJobs.ServiceBus.Triggers.BrokeredMessageToStringConverter.ConvertAsync(BrokeredMessage input, CancellationToken cancellationToken)
 at Microsoft.Azure.WebJobs.ServiceBus.Triggers.ConverterArgumentBindingProvider`1.ConverterArgumentBinding.<BindAsync>d__0.MoveNext()

编辑:WebJobs 文档建议不仅我所做的工作 (String) 有效，ServiceBusTrigger 也应该自动反序列化 JSON 对象。但是，如果我尝试取出 POCO，我仍然会收到 XML 反序列化错误。有趣的是，如果我将类型设置为 Byte[]，我也会收到 XML 反序列化错误，这也应该可以工作。

编辑2:Stream也不起作用。看来只有 BrokeredMessage 适用于触发器，而 GetBody 是我能找到的从 BrokeredMessage 中获取字符串的唯一方法。

Answer 1

我能够通过添加自定义消息处理器来完成反序列化工作。

自定义消息处理器示例位于 https://github.com/Azure/azure-webjobs-sdk-samples/tree/master/BasicSamples/MiscOperations

您将 ContentType 设置为 application/json，如下所示 -

public class CustomMessagingProvider : MessagingProvider
{
    private readonly ServiceBusConfiguration _config;

    public CustomMessagingProvider(ServiceBusConfiguration config) : base(config)
    {
        _config = config;
    }

    public override MessageProcessor CreateMessageProcessor(string entityPath)
    {
        return new CustomMessageProcessor(_config.MessageOptions);
    }

    private class CustomMessageProcessor : MessageProcessor
    {
        public CustomMessageProcessor(OnMessageOptions messageOptions)
            : base(messageOptions)
        {
        }

        public override Task<bool> BeginProcessingMessageAsync(BrokeredMessage message, CancellationToken cancellationToken)
        {
            message.ContentType = "application/json";

            return base.BeginProcessingMessageAsync(message, cancellationToken);
        }
    }
}

然后，您可以在 webjob 中配置 ServiceBusConfiguration 时设置此消息处理器。

 JobHostConfiguration config = new JobHostConfiguration();
        ServiceBusConfiguration serviceBusConfig = new ServiceBusConfiguration
        {
            ConnectionString = _servicesBusConnectionString
        };

        serviceBusConfig.MessagingProvider = new CustomMessagingProvider(serviceBusConfig);

        config.UseServiceBus(serviceBusConfig);