AZ-204 Blob存储教程代码报错：Stream does not support reading

问题情况 #

学习微软AZ-204认证的《使用Blob存储开发解决方案》教程时，完全复制教程代码运行，容器可在Azure门户正常创建，但执行文件上传至Blob步骤时抛出以下异常：

Unhandled exception. System.NotSupportedException: Stream does not support reading.
   at System.IO.Strategies.BufferedFileStreamStrategy.CopyToAsync(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)
   at System.IO.FileStream.CopyToAsync(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)
   at Azure.Storage.NonDisposingStream.CopyToAsync(Stream destination, Int32 bufferSize, CancellationToken cancellationToken)
   at Azure.Core.RequestContent.StreamContent.WriteToAsync(Stream stream, CancellationToken cancellation)
   at Azure.Core.Pipeline.HttpClientTransport.PipelineRequest.PipelineContentAdapter.SerializeToStreamAsync(Stream stream, TransportContext context, CancellationToken cancellationToken)
   at System.Net.Http.HttpContent.<CopyToAsync>g__WaitAsync|56_0(ValueTask copyTask)
   at System.Net.Http.HttpConnection.SendRequestContentAsync(HttpRequestMessage request, HttpContentWriteStream stream, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnection.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnection.SendAsyncCore(HttpRequestMessage request, Boolean async, CancellationToken cancellationToken)
   at System.Net.Http.HttpConnectionPool.SendWithVersionDetectionAndRetryAsync(HttpRequestMessage request, Boolean async, Boolean doRequestAuth, CancellationToken cancellationToken)
   at System.Net.Http.HttpClient.<SendAsync>g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)
   at Azure.Core.Pipeline.HttpClientTransport.ProcessAsync(HttpMessage message, Boolean async)
   at Azure.Core.Pipeline.HttpPipelineTransportPolicy.ProcessAsync(HttpMessage message, ReadOnlyMemory`1 pipeline)
   at Azure.Core.Pipeline.ResponseBodyPolicy.ProcessAsync(HttpMessage message, ReadOnlyMemory`1 pipeline, Boolean async)
   at Azure.Core.Pipeline.HttpPipelineSynchronousPolicy.<ProcessAsync>g__ProcessAsyncInner|4_0(HttpMessage message, ReadOnlyMemory`1 pipeline)
onary`2 metadata, IDictionary`2 tags, BlobRequestConditions conditions, Nullable`1 accessTier, BlobImmutabilityPolicy immutabilityPolicy, Nullable`1 legalHold, IProgress`1 progressHandler, UploadTransferValidationOptions transferValidationOverride, String operationName, Boolean async, CancellationToken cancellationToken)
   at Azure.Storage.Blobs.Specialized.BlockBlobClient.<>c__DisplayClass64_0.<<GetPartitionedUploaderBehaviors>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Azure.Storage.PartitionedUploader`2.UploadInternal(Stream content, Nullable`1 expectedContentLength, TServiceSpecificData args, IProgress`1 progressHandler, Boolean async, CancellationToken cancellationToken)
   at Azure.Storage.Blobs.BlobClient.StagedUploadInternal(Stream content, BlobUploadOptions options, Boolean async, CancellationToken cancellationToken)
   at Azure.Storage.Blobs.BlobClient.UploadAsync(Stream content)
   at Program.<<Main>$>g__ProcessAsync|0_0() in C:\Users\[redacted]\Documents\devops\working with blob storage module\az204-blob\Program.cs:line 51
   at Program.<Main>$(String[] args) in C:\Users\[redacted]\Documents\devops\working with blob storage module\az204-blob\Program.cs:line 7

执行的完整代码如下：

using Azure.Storage.Blobs;
using Azure.Storage.Blobs.Models;

Console.WriteLine("Azure Blob Storage exercise\n");

// Run the examples asynchronously, wait for the results before proceeding
ProcessAsync().GetAwaiter().GetResult();

Console.WriteLine("Press enter to exit the sample application.");
Console.ReadLine();

static async Task ProcessAsync()
{
    // Copy the connection string from the portal in the variable below.
    string storageConnectionString = "[redacted]";

    // Create a client that can authenticate with a connection string
    BlobServiceClient blobServiceClient = new BlobServiceClient(storageConnectionString);

    // COPY EXAMPLE CODE BELOW HERE
    
    // CREATE A CONTAINER
    //Create a unique name for the container
    string containerName = "wtblob" + Guid.NewGuid().ToString();

    // Create the container and return a container client object
    BlobContainerClient containerClient = await blobServiceClient.CreateBlobContainerAsync(containerName);
    Console.WriteLine("A container named '" + containerName + "' has been created. " +
        "\nTake a minute and verify in the portal." + 
        "\nNext a file will be created and uploaded to the container.");
    Console.WriteLine("Press 'Enter' to continue.");
    Console.ReadLine();
    
    // UPLOAD BLOBS TO A CONTAINER
    // Create a local file in the ./data/ directory for uploading and downloading
    string localPath = "./data/";
    string fileName = "wtfile" + Guid.NewGuid().ToString() + ".txt";
    string localFilePath = Path.Combine(localPath, fileName);

    // Write text to the file
    await File.WriteAllTextAsync(localFilePath, "Hello, World!");

    // Get a reference to the blob
    BlobClient blobClient = containerClient.GetBlobClient(fileName);

    Console.WriteLine("Uploading to Blob storage as blob:\n\t {0}\n", blobClient.Uri);

    // Open the file and upload its data
    using (FileStream uploadFileStream = File.OpenWrite(localFilePath))
        {
    await blobClient.UploadAsync(uploadFileStream);
    uploadFileStream.Close();
        }

    Console.WriteLine("\nThe file was uploaded. We'll verify by listing" + 
            " the blobs next.");
    Console.WriteLine("Press 'Enter' to continue.");
    Console.ReadLine();
    
    // LIST THE BLOBS IN A CONTAINER
    // List blobs in the container
    Console.WriteLine("Listing blobs...");
    await foreach (BlobItem blobItem in containerClient.GetBlobsAsync())
    {
        Console.WriteLine("\t" + blobItem.Name);
    }

    Console.WriteLine("\nYou can also verify by looking inside the " + 
            "container in the portal." +
            "\nNext the blob will be downloaded with an altered file name.");
    Console.WriteLine("Press 'Enter' to continue.");
    Console.ReadLine();
    
    // DOWNLOAD BLOBS
    // Download the blob to a local file
    // Append the string "DOWNLOADED" before the .txt extension 
    string downloadFilePath = localFilePath.Replace(".txt", "DOWNLOADED.txt");

    Console.WriteLine("\nDownloading blob to\n\t{0}\n", downloadFilePath);

    // Download the blob's contents and save it to a file
    BlobDownloadInfo download = await blobClient.DownloadAsync();

    using (FileStream downloadFileStream = File.OpenWrite(downloadFilePath))
    {
        await download.Content.CopyToAsync(downloadFileStream);
    }
    Console.WriteLine("\nLocate the local file in the data directory created earlier to verify it was downloaded.");
    Console.WriteLine("The next step is to delete the container and local files.");
    Console.WriteLine("Press 'Enter' to continue.");
    Console.ReadLine();
    
    // DELETE A CONTAINER
    // Delete the container and clean up local files created
    Console.WriteLine("\n\nDeleting blob container...");
    await containerClient.DeleteAsync();

    Console.WriteLine("Deleting the local source and downloaded files...");
    File.Delete(localFilePath);
    File.Delete(downloadFilePath);

    Console.WriteLine("Finished cleaning up.");
    
    
}

修复方案 #

核心原因 #

代码中使用File.OpenWrite(localFilePath)打开文件流，该方法返回的是只写模式的流，不支持读取操作；而Azure Blob的UploadAsync()方法需要从流中读取数据完成上传，因此抛出Stream does not support reading异常。

具体修复 #

将文件打开方式从File.OpenWrite()改为File.OpenRead()，获取可读的文件流：

// 修正后的上传代码块
using (FileStream uploadFileStream = File.OpenRead(localFilePath))
{
    await blobClient.UploadAsync(uploadFileStream);
}

注意：using语句会自动释放流资源，无需手动调用Close()方法。

额外说明 #

如果坚持使用File.OpenWrite()，需要在写完文件后将流的位置重置到起始位置，但这种方式没必要（因为已经通过WriteAllTextAsync完成了文件写入），直接使用File.OpenRead()是更简洁正确的方案。

内容的提问来源于stack exchange，提问作者Anna