Question

我需要从存储帐户下载大型备份文件。我使用SAS进行尝试，并生成链接，当我使用该链接并输入该链接时直接将其下载到浏览器中会下载文件，但是当我尝试通过我的代码下载文件时，它将给我空文件或根本不下载文件。注释掉的行是我已经尝试过的，最后一个是Redirect（blobSasuri）;

public async Task DownloadBlobItemAsync([FromQuery] string userId, [FromRoute] string fileName, [FromBody] PathObject path, [FromRoute] int filestorageConnectionId)
{
    var fileStorageConnection = await _customerProvider.GetFileStorageConnection(filestorageConnectionId);
    var customer = await _customerProvider.GetCustomer(fileStorageConnection.CustomerId);

    CloudBlockBlob blob = _fileStorage.DownloadBlobFile(fileStorageConnection.Id, userId, customer.Id, fileName, path.Path);

    var sas = blob.GetSharedAccessSignature(new SharedAccessBlobPolicy()
    {
        SharedAccessStartTime = DateTime.UtcNow.AddHours(-5),
        SharedAccessExpiryTime = DateTime.UtcNow.AddHours(5),
        Permissions = SharedAccessBlobPermissions.Read
    });

    string blobSasUri = (string.Format(CultureInfo.InvariantCulture, "{0}{1}", blob.Uri, sas));

    // CloudBlockBlob blobNew = new CloudBlockBlob(new Uri(blobSasUri));

    // var pathNew = Directory.GetCurrentDirectory();
    // blobNew.DownloadToFileAsync(pathNew, FileMode.Create);

    //await blob.DownloadToFileAsync(blobSasUri, FileMode.Create);

    Redirect(blobSasUri);

    //using (var client = new WebClient())
    //{
    //    client.DownloadFile(blobSasUri, fileName);
    //}
}

Answer 1

我不知道您用什么方法下载Blob，我用blobSas.DownloadToStream()测试了一下，它对我有用。所以也许您可以尝试使用我的代码。

 static void Main(string[] args)
    {
        string storageConnectionString = "connectin string";

        // Check whether the connection string can be parsed.
        CloudStorageAccount storageAccount;

        CloudStorageAccount.TryParse(storageConnectionString, out storageAccount);

        var containerName = "test";
        var blobName = "testfile.zip";
        string saveFileName = @"E:\testfilefolder\myfile1.zip";

        var blobContainer = storageAccount.CreateCloudBlobClient().GetContainerReference(containerName);
        var blob = blobContainer.GetBlockBlobReference(blobName);
        var sas =blob.GetSharedAccessSignature(new SharedAccessBlobPolicy()
        {
            SharedAccessStartTime = DateTime.UtcNow.AddHours(-5),
            SharedAccessExpiryTime = DateTime.UtcNow.AddHours(5),
            Permissions = SharedAccessBlobPermissions.Read
        });
        string blobSasUri = (string.Format(CultureInfo.InvariantCulture, "{0}{1}", blob.Uri, sas));

        //Download Blob through SAS url
        CloudBlockBlob blobSas = new CloudBlockBlob(new Uri(blobSasUri));

        long startPosition = 0;
        using (MemoryStream ms = new MemoryStream())
        {
            blobSas.DownloadToStream(ms);
            byte[] data = new byte[ms.Length];
            ms.Position = 0;
            ms.Read(data, 0, data.Length);

            using (FileStream fs = new FileStream(saveFileName, FileMode.OpenOrCreate))
            {
                fs.Position = startPosition;
                fs.Write(data, 0, data.Length);
            }
        }
    }

除了使用sas url下载大的blob之外，另一种选择是以大块形式提供文件。这是代码。

        int segmentSize = 1 * 1024 * 1024;//1 MB chunk

        var blobContainer = storageAccount.CreateCloudBlobClient().GetContainerReference(containerName);
        var blob = blobContainer.GetBlockBlobReference(blobName);
        blob.FetchAttributes();
        var blobLengthRemaining = blob.Properties.Length;
        long startPosition = 0;
        string saveFileName = @"E:\testfilefolder\myfile.zip";
        do
        {
            long blockSize = Math.Min(segmentSize, blobLengthRemaining);
            byte[] blobContents = new byte[blockSize];
            using (MemoryStream ms = new MemoryStream())
            {
                blob.DownloadRangeToStream(ms, startPosition, blockSize);
                ms.Position = 0;
                ms.Read(blobContents, 0, blobContents.Length);
                using (FileStream fs = new FileStream(saveFileName, FileMode.OpenOrCreate))
                {
                    fs.Position = startPosition;
                    fs.Write(blobContents, 0, blobContents.Length);
                }
            }
            startPosition += blockSize;
            blobLengthRemaining -= blockSize;
        }
        while (blobLengthRemaining > 0);

希望这可以为您提供帮助，如果仍然有其他问题，请随时告诉我。

Answer 2

这不适用于我和大于5 GB的大文件。我所做的是我返回了文件的路径，并在其上添加了SAS，并将其返回到前端。因此，现在在前端，我已经与sas链接，并且可以通过浏览器直接将其下载到那里。

尝试下载较大的Blob文件

2 个答案: