使用C#反序列化Avro文件

Question

我找不到用C#反序列化Apache Avro文件的方法.Avro文件是Microsoft Azure Event Hub中的存档功能生成的文件.

使用Java,我可以使用Apache的Avro Tools将文件转换为JSON:

java -jar avro-tools-1.8.1.jar tojson --pretty inputfile > output.json

使用NuGet包Microsoft.Hadoop.Avro我能提取SequenceNumber,Offset和EnqueuedTimeUtc,但因为我不知道该用什么类型Body的异常被抛出.我试过Dictionary<string, object>和其他类型.

static void Main(string[] args)
{
    var fileName = "...";

    using (Stream stream = new FileStream(fileName, FileMode.Open, FileAccess.Read, FileShare.Read))
    {
        using (var reader = AvroContainer.CreateReader<EventData>(stream))
        {
            using (var streamReader = new SequentialReader<EventData>(reader))
            {
                var record = streamReader.Objects.FirstOrDefault();
            }
        }
    }
}

[DataContract(Namespace = "Microsoft.ServiceBus.Messaging")]
public class EventData
{
    [DataMember(Name = "SequenceNumber")]
    public long SequenceNumber { get; set; }

    [DataMember(Name = "Offset")]
    public string Offset { get; set; }

    [DataMember(Name = "EnqueuedTimeUtc")]
    public string EnqueuedTimeUtc { get; set; }

    [DataMember(Name = "Body")]
    public foo Body { get; set; }

    // More properties...
}

架构如下所示:

{
  "type": "record",
  "name": "EventData",
  "namespace": "Microsoft.ServiceBus.Messaging",
  "fields": [
    {
      "name": "SequenceNumber",
      "type": "long"
    },
    {
      "name": "Offset",
      "type": "string"
    },
    {
      "name": "EnqueuedTimeUtc",
      "type": "string"
    },
    {
      "name": "SystemProperties",
      "type": {
        "type": "map",
        "values": [ "long", "double", "string", "bytes" ]
      }
    },
    {
      "name": "Properties",
      "type": {
        "type": "map",
        "values": [ "long", "double", "string", "bytes" ]
      }
    },
    {
      "name": "Body",
      "type": [ "null", "bytes" ]
    }
  ]
}    

Answer 1

我终于能够让它与 Apache C# 库/框架一起工作。
我被困了一段时间，因为 Azure 事件中心的捕获功能有时会输出一个没有任何消息内容的文件。我可能还对消息最初如何序列化到 EventData 对象中存在疑问。
下面的代码适用于从捕获 blob 容器保存到磁盘的文件。

var dataFileReader = DataFileReader<EventData>.OpenReader(file);
foreach (var record in dataFileReader.NextEntries)
{
   // Do work on EventData object
}

这也适用于使用 GenericRecord 对象。

var dataFileReader = DataFileReader<GenericRecord>.OpenReader(file);

这需要一些努力才能弄清楚。不过，我现在同意 Azure 事件中心捕获功能是备份所有事件的绝佳功能。我仍然觉得他们应该使格式可选，就像他们对流分析作业输出所做的那样，但也许我会习惯 Avro。

Answer 2

我能够使用完整的数据访问工作dynamic.这是访问原始body数据的代码,它存储为一个字节数组.在我的例子中,这些字节包含UTF8编码的JSON,但当然这取决于您最初创建EventData发布到事件中心的实例的方式:

using (var reader = AvroContainer.CreateGenericReader(stream))
{
    while (reader.MoveNext())
    {
        foreach (dynamic record in reader.Current.Objects)
        {
            var sequenceNumber = record.SequenceNumber;
            var bodyText = Encoding.UTF8.GetString(record.Body);
            Console.WriteLine($"{sequenceNumber}: {bodyText}");
        }
    }
}

如果有人可以发布一个静态类型的解决方案,我会支持它,但考虑到任何系统中更大的延迟几乎肯定是与Event Hub Archive blob的连接,我不担心解析性能.:)

Answer 3

本要点展示了如何使用Microsoft.Hadoop.Avro2使用C#反序列化事件中心捕获,它具有兼容.NET Framework 4.5和.NET Standard 1.6的优点:

 var connectionString = "<Azure event hub capture storage account connection string>";
 var containerName = "<Azure event hub capture container name>";
 var blobName = "<Azure event hub capture BLOB name (ends in .avro)>";

 var storageAccount = CloudStorageAccount.Parse(connectionString);
 var blobClient = storageAccount.CreateCloudBlobClient();
 var container = blobClient.GetContainerReference(containerName);
 var blob = container.GetBlockBlobReference(blobName);
 using (var stream = blob.OpenRead())
 using (var reader = AvroContainer.CreateGenericReader(stream))
     while (reader.MoveNext())
         foreach (dynamic result in reader.Current.Objects)
         {
             var record = new AvroEventData(result);
             record.Dump();
         }

 public struct AvroEventData
 {
     public AvroEventData(dynamic record)
     {
         SequenceNumber = (long) record.SequenceNumber;
         Offset = (string) record.Offset;
         DateTime.TryParse((string) record.EnqueuedTimeUtc, out var enqueuedTimeUtc);
         EnqueuedTimeUtc = enqueuedTimeUtc;
         SystemProperties = (Dictionary<string, object>) record.SystemProperties;
         Properties = (Dictionary<string, object>) record.Properties;
         Body = (byte[]) record.Body;
     }
     public long SequenceNumber { get; set; }
     public string Offset { get; set; }
     public DateTime EnqueuedTimeUtc { get; set; }
     public Dictionary<string, object> SystemProperties { get; set; }
     public Dictionary<string, object> Properties { get; set; }
     public byte[] Body { get; set; }
 }

• NuGet参考:

  • Microsoft.Hadoop.Avro2(1.2.1有效)
  • WindowsAzure.Storage(8.3.0有效)

• 命名空间:

  • Microsoft.Hadoop.Avro.Container
  • Microsoft.WindowsAzure.Storage