Question

如何正确处理“＆＃34;提交的块数不能超过50,000个块的最大限制。＆＃34;执行CloudAppendBlob.AppendTextAsync？

时出现异常

我目前有以下代码：

    private async Task MessageLogger()
    {
        string messages = "";
        while (true)
        {
            // Check if a new log file should be created
            if (DateTime.UtcNow.Day != _logCreatedUtc.Day)
            {
                // Create a new log file
                await CreateNewLogAsync();
            }

            if (_messageQueue.Count == 0 && messages.Length == 0)
            {
                await Task.Delay(50);
                continue;
            }

            int n = 0;
            while ((this._messageQueue.Count > 0) && (n < 50))
            {
                string message;
                if (this._messageQueue.TryPeek(out message))
                {
                    messages += message;
                    this._messageQueue.TryDequeue(out message);
                    n++;
                }
            }

            try
            {
                // Append messages to Azure Blob
                await _appendBlob.AppendTextAsync(messages);
                messages = "";
            }
            catch (Microsoft.WindowsAzure.Storage.StorageException exception)
                when(exception.RequestInformation.HttpStatusCode == 404)
            {
                // Log file was deleted. Create a new log file
                await CreateNewLogAsync();
            }
            catch (Exception exception)
            {
                LogException("Exception from CloudAppendBlob.AppendTextAsync", exception);
                await Task.Delay(1000);
            }
        }
    }

我的代码中有时会因为通用异常处理程序而记录以下类型的异常：

01.04.2018 22:17:03.030 - <<EXCEPTION>>: Exception from CloudAppendBlob.AppendTextAsync
01.04.2018 22:17:03.044 - <<EXCEPTION>>: Type =<System.AggregateException> Message =<One or more errors occurred. (One or more errors occurred. (The committed block count cannot exceed the maximum limit of 50,000 blocks.))> InnerException.Message=<One or more errors occurred. (The committed block count cannot exceed the maximum limit of 50,000 blocks.)>
   at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
   at Microsoft.WindowsAzure.Storage.Blob.BlobWriteStream.<Dispose>b__8_0()
   at Microsoft.WindowsAzure.Storage.Core.Util.CommonUtility.RunWithoutSynchronizationContext(Action actionToRun)
   at Microsoft.WindowsAzure.Storage.Blob.BlobWriteStream.Dispose(Boolean disposing)
   at System.IO.Stream.Close()
   at System.IO.Stream.Dispose()
   at Microsoft.WindowsAzure.Storage.Blob.CloudAppendBlob.<UploadFromStreamAsyncHelper>d__34.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
   at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
   at Infrastructure.Logging.AzureBlob.Logger.<MessageLogger>d__24.MoveNext() in /opt/vsts/work/1/s/Infrastructure/Logging/Infrastructure.Logging.AzureBlob/Logger.cs:line 183

异常处理程序如何捕获这种错误？我想为它添加一个特定的处理程序。

我试图查看调试器，但看起来很奇怪：

异常变量看起来像＆＃34; null＆＃34;在调试器中，但实际上它没有，它被记录正确。

Answer 1

我与产品团队进行了核实，他们建议实施并使用AccessConditions进行块附加，以避免发生异常：

 /// <summary>
    /// Gets or sets a value for a condition that specifies the maximum size allowed for an append blob when a new block is committed. The append
    /// will succeed only if the size of the blob after the append operation is less than or equal to the specified size.
    /// </summary>
    /// <value>The maximum size in bytes, or <c>null</c> if no value is set.</value>
    /// <remarks>This condition only applies to append blobs.</remarks>
    public long? IfMaxSizeLessThanOrEqual

基本上你将检查块的数量，并根据条件，你可以开始一个新的blob追加（如果达到最大值），或继续追加。

这两个会有所帮助：

x-ms-blob-condition-maxsize ：客户端可以使用此标头确保追加操作不会将blob大小增加到超出预期的最大大小（以字节为单位）。如果条件失败，请求将失败并出现MaxBlobSizeConditionNotMet错误（HTTP状态代码412 - Precondition Failed）。

x-ms-blob-condition-appendpos 可选条件标头，仅用于附加块操作。一个数字，指示要比较的字节偏移量。仅当追加位置等于此数字时，追加阻止才会成功。如果不是，则请求将因AppendPositionConditionNotMet错误而失败（HTTP状态代码412 - Precondition Failed）。

<强>来源：** https://github.com/Azure/azure-storage-net/blob/master/Lib/Common/AccessCondition.cs **

https://docs.microsoft.com/en-us/rest/api/storageservices/append-block

Answer 2

您的异常包含在AggregateException中。这就是你打开和处理它的方法：

catch (Exception exception)
{
    ExtractStorageError(exception);
}

。。

private static string ExtractStorageError(Exception ex) {   
    while (ex != null && !(ex is StorageException))     
    {       
        ex = (ex.InnerException != null) ? ex.InnerException.GetBaseException() : ex.InnerException;
    }   
    if (ex is StorageException)     
    {   
        StorageException se = ex as StorageException;    
        if(ste.RequestInformation.ExtendedErrorInformation != null)
           return se.RequestInformation.ExtendedErrorInformation.ErrorCode;     
    }   
    return null; 
}

如何处理追加blob异常？

2 个答案: