C# 大文件下载可从 azure blob 存储恢复

Question

我真的需要一些橡皮鸭...

我有一个至少为 2.3 GiB 的文件。我目前正在将此文件下载到临时目录。但是当下载中断时（连接错误，或 windows 崩溃）我希望用户从停止的地方恢复下载。而不是重新下载整个文件。该代码的工作原理是它继续下载文件，但我看到下载流又从头开始了。所以这意味着文件最终为（2.3 GiB + 之前下载的字节数），这会损坏我的文件。

我使用了以下代码片段来恢复下载，所以我希望流能在停止的地方恢复 localStream.Seek(positionInFile, SeekOrigin.Begin);

关于我在这里遗漏的任何想法？这是我的代码。

                BlobContainerClient containerClient = new BlobContainerClient(connectionString, container);
                var blobClient = containerClient.GetBlobClient(downloadFile);

                fullOutputPath = createOutputFilePath(updateFileUri.OriginalString, outputFolder);
                downloadFileInfo = new FileInfo(fullOutputPath);

                var response = blobClient.Download(cts.Token);
                contentLength = response.Value.ContentLength;
                if (contentLength.HasValue && contentLength.Value > 0)
                {
                    if (_fileSystemService.FileExists(fullOutputPath))
                    {
                        from = downloadFileInfo.Length;
                        to = contentLength;

                        if (from == to)
                        {
                            //file is already downloaded
                            //skip it
                            progress.Report(1);
                            return;
                        }
                        fileMode = FileMode.Open;
                        positionInFile = downloadFileInfo.Length;
                    }

                    using FileStream localStream = _fileSystemService.CreateFile(fullOutputPath, fileMode, FileAccess.Write);
                    localStream.Seek(positionInFile, SeekOrigin.Begin);

                    bytesDownloaded = positionInFile;
                    double dprog = ((double)bytesDownloaded / (double)(contentLength.Value + positionInFile));
                    do
                    {
                        bytesRead = await response.Value.Content.ReadAsync(buffer, 0, buffer.Length, cts.Token);

                        await localStream.WriteAsync(buffer, 0, bytesRead, cts.Token);
                        await localStream.FlushAsync();

                        bytesDownloaded += bytesRead;
                        dprog = ((double)bytesDownloaded / (double)(contentLength.Value + positionInFile));
                        progress.Report(dprog);

                    } while (bytesRead > 0);
                }

Answer 1

我为您做了一些测试，就我而言，我使用.txt 文件来演示您的要求。您可以看到 .txt 文件 here。如您所见，在第 151 行，我做了一个结束标记：

我还创建了一个以这个结束标记结尾的本地文件来模拟下载中断，我们将继续从存储中下载：

下面是我的快速演示代码：

static void Main(string[] args)
{
    string containerName = "container name";
    string blobName = ".txt file name";
    string storageConnStr = "storage account conn str";

    string localFilePath = @"local file path";

    var localFileStream = new FileStream(localFilePath, FileMode.Append);

    var localFileLength = new FileInfo(localFilePath).Length;

    localFileStream.Seek(localFileLength, SeekOrigin.Begin);


    var blobServiceClient = new BlobServiceClient(storageConnStr);
    var blobClient = blobServiceClient.GetBlobContainerClient(containerName).GetBlobClient(blobName);

    var stream = blobClient.Download(new Azure.HttpRange(localFileLength)).Value.Content;

    var contentStrting = new StreamReader(stream).ReadToEnd();

    Console.WriteLine(contentStrting);

    localFileStream.Write(Encoding.ASCII.GetBytes(contentStrting));
    localFileStream.Flush();
}

结果：我们只下载了结束标志后面的内容：

内容已下载到本地 .txt 文件：

如果您还有其他问题，请告诉我。

C# 大文件下载可从 azure blob 存储恢复

C# big filedownload resumable from azure blob storage

c#

azure

azure-storage