StorageException通过慢速网络下载大文件时 [英] StorageException when downloading a large file over a slow network

问题描述

我使用的NuGet包 WindowsAzure.Storage 版本4.2.1。

I'm using the NuGet package WindowsAzure.Storage version 4.2.1.

以下code试图从在一个遥远的数据中心存储容器下载Blob的。

The following code tries to download a blob from a storage container that is in a distant datacenter.

try
{
    var blobRequestOptions = new BlobRequestOptions
    {
        RetryPolicy = new ExponentialRetry(TimeSpan.FromSeconds(5), 3),
        MaximumExecutionTime = TimeSpan.FromMinutes(60),
        ServerTimeout = TimeSpan.FromMinutes(60)
    };
    using (var fileStream = File.Create(localPath))
    {
        blockBlob.DownloadToStream(fileStream, null, blobRequestOptions);
    }
}
catch (Exception e)
{
    Console.WriteLine(e.Message);
}

不过，有时它下载了大约10分钟，然后将它抛出以下异常：

However, sometimes it downloads for ~10 minutes and then it throws the following exception:

Unhandled Exception: Microsoft.WindowsAzure.Storage.StorageException: The client could not finish the operation within specified timeout. ---> System.TimeoutException: The client could not finish the operation within specified timeout.
--- End of inner exception stack trace ---
at Microsoft.WindowsAzure.Storage.Core.Util.StorageAsyncResult`1.End()
at Microsoft.WindowsAzure.Storage.Blob.CloudBlockBlob.EndUploadText(IAsyncResult asyncResult)
at Microsoft.WindowsAzure.Storage.Core.Util.AsyncExtensions.<>c__DisplayClass4.b__3(IAsyncResult ar)
--- End of stack trace from previous location where exception was thrown ---

我该如何解决这个问题？

推荐答案

请试试这个code。基本上它是它会创建一个空文件，然后再使用1 MB块读取blob数据<一个href=\"https://msdn.microsoft.com/en-us/library/microsoft.windowsazure.storage.blob.cloudblockblob.downloadrangetostream.aspx\"相对=nofollow> DownloadRangeToStream 方法。由于大块获取下载，它是附加到文件中。

Please try this code. Basically what it does is it creates an empty file first and then read the blob's data in 1 MB chunks using DownloadRangeToStream method. As the chunks get downloaded, it appends it to the file.

    private static void DownloadLargeFile()
    {
        var account = new CloudStorageAccount(new StorageCredentials(accountName, accountKey), true);
        var blobClient = account.CreateCloudBlobClient();
        var container = blobClient.GetContainerReference("container-name");
        var file = "my-very-large-file-name";
        var blob = container.GetBlockBlobReference(file);
        //First fetch the size of the blob. We use this to create an empty file with size = blob's size
        blob.FetchAttributes();
        var blobSize = blob.Properties.Length;
        long blockSize = (1 * 1024 * 1024);//1 MB chunk;
        blockSize = Math.Min(blobSize, blockSize);
        //Create an empty file of blob size
        using (FileStream fs = new FileStream(file, FileMode.Create))//Create empty file.
        {
            fs.SetLength(blobSize);//Set its size
        }
        var blobRequestOptions = new BlobRequestOptions
        {
            RetryPolicy = new ExponentialRetry(TimeSpan.FromSeconds(5), 3),
            MaximumExecutionTime = TimeSpan.FromMinutes(60),
            ServerTimeout = TimeSpan.FromMinutes(60)
        };
        long currentPointer = 0;
        long bytesRemaining = blobSize;
        do
        {
            var bytesToFetch = Math.Min(blockSize, bytesRemaining);
            using (MemoryStream ms = new MemoryStream())
            {
                //Download range (by default 1 MB)
                blob.DownloadRangeToStream(ms, currentPointer, bytesToFetch, null, blobRequestOptions);
                ms.Position = 0;
                var contents = ms.ToArray();
                using (var fs = new FileStream(file, FileMode.Open))//Open that file
                {
                    fs.Position = currentPointer;//Move the cursor to the end of file.
                    fs.Write(contents, 0, contents.Length);//Write the contents to the end of file.
                }
                currentPointer += contents.Length;//Update pointer
                bytesRemaining -= contents.Length;//Update bytes to fetch
            }
        }
        while (bytesRemaining > 0);
    }

我试过在一个小本文件code（差互联网连接：P）。与500 MB的文件尝试之前 - 所以，请您先尝试一下在一个小文件（10 MB左右说5）。 HTH。

I've tried this code on a small file (Poor Internet Connectivity :P). So please try it out first on a small file (say around 5 - 10 MB) before trying with your 500 MB file. HTH.

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