C# 为什么CloudBlockBlob.DownloadToStream总是返回空流？

我有以下代码：

public static void UploadStreamToBlob(Stream stream, string containerName, string blobName)
{
    CloudStorageAccount storageAccount = 
        CloudStorageAccount.Parse(CloudConfigurationManager.GetSetting("StorageConnectionString"));
    CloudBlobClient blobClient = storageAccount.CreateCloudBlobClient();

    CloudBlobContainer blobContainer = blobClient.GetContainerReference(containerName);
    blobContainer.CreateIfNotExists();
    blobContainer.SetPermissions(
        new BlobContainerPermissions
        {
            PublicAccess = BlobContainerPublicAccessType.Blob
        });

    CloudBlockBlob blockBlob = blobContainer.GetBlockBlobReference(blobName);
    long streamlen = stream.Length;  <-- This shows 203 bytes
    blockBlob.UploadFromStream(stream);        
}

public static void UploadStreamToBlob（流、字符串containerName、字符串blobName）
{
CloudStorageAccount storageAccount=
解析（CloudConfigurationManager.GetSetting（“StorageConnectionString”）；
CloudBlobClient blobClient=storageAccount.CreateCloudBlobClient（）；
CloudBlobContainer blobContainer=blobClient.GetContainerReference（containerName）；
blobContainer.CreateIfNotExists（）；
blobContainer.SetPermissions(
新BlobContainerPermissions
{
PublicAccess=BlobContainerPublicAccessType.Blob
});
CloudBlockBlob blockBlob=blobContainer.getblockblobbreference（blobName）；
long streamlen=stream.Length；啊，我算出来了

以下几行：

long streamlen = stream.Length;
blockBlob.UploadFromStream(stream);   

需要改成

long streamlen = stream.Length;  
stream.Position = 0;
blockBlob.UploadFromStream(stream);   

+1：刚刚帮我摆脱了一个空Blob下载场景…通常是简单的细节让我们绊倒。这是处理流时的常见问题。我将所有设置都设置为IO方法
stream.Seek（0，SeekOrigin.Begin）；
long streamlen = stream.Length;  
stream.Position = 0;
blockBlob.UploadFromStream(stream);