在 MVC3 中下载 Azure Blob 文件

Question

我们的 ASP.NET MVC 3 应用程序在 Azure 上运行并使用 Blob 作为文件存储。我已经弄清楚了上传部分。

视图将具有文件名，单击该文件名将提示出现文件下载屏幕。

谁能告诉我该怎么做？

Answer 1

确实有两个选项...第一个是直接将用户重定向到 blob（如果 blob 在公共容器中）。看起来有点像：

return Redirect(container.GetBlobReference(name).Uri.AbsoluteUri);

如果 blob 位于私有容器中，您可以使用共享访问签名并像前面的示例一样执行重定向，或者您可以在控制器操作中读取 blob 并将其作为下载推送到客户端：

Response.AddHeader("Content-Disposition", "attachment; filename=" + name); // force download
container.GetBlobReference(name).DownloadToStream(Response.OutputStream);
return new EmptyResult();

Answer 2

这是私有 blob 访问的可恢复版本（适用于大文件或允许在视频或音频播放中查找）：

public class AzureBlobStream : ActionResult
{
    private string filename, containerName;

    public AzureBlobStream(string containerName, string filename)
    {
        this.containerName = containerName;
        this.filename = filename;
        this.contentType = contentType;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        var response = context.HttpContext.Response;
        var request = context.HttpContext.Request;

        var connectionString = ConfigurationManager.ConnectionStrings["Storage"].ConnectionString;
        var account = CloudStorageAccount.Parse(connectionString);
        var client = account.CreateCloudBlobClient();
        var container = client.GetContainerReference(containerName);
        var blob = container.GetBlockBlobReference(filename);

        blob.FetchAttributes();
        var fileLength = blob.Properties.Length;
        var fileExists = fileLength > 0;
        var etag = blob.Properties.ETag;

        var responseLength = fileLength;
        var buffer = new byte[4096];
        var startIndex = 0;

        //if the "If-Match" exists and is different to etag (or is equal to any "*" with no resource) then return 412 precondition failed
        if (request.Headers["If-Match"] == "*" && !fileExists ||
            request.Headers["If-Match"] != null && request.Headers["If-Match"] != "*" && request.Headers["If-Match"] != etag)
        {
            response.StatusCode = (int)HttpStatusCode.PreconditionFailed;
            return;
        }

        if (!fileExists)
        {
            response.StatusCode = (int)HttpStatusCode.NotFound;
            return;
        }

        if (request.Headers["If-None-Match"] == etag)
        {
            response.StatusCode = (int)HttpStatusCode.NotModified;
            return;
        }

        if (request.Headers["Range"] != null && (request.Headers["If-Range"] == null || request.Headers["IF-Range"] == etag))
        {
            var match = Regex.Match(request.Headers["Range"], @"bytes=(\d*)-(\d*)");
            startIndex = Util.Parse<int>(match.Groups[1].Value);
            responseLength = (Util.Parse<int?>(match.Groups[2].Value) + 1 ?? fileLength) - startIndex;
            response.StatusCode = (int)HttpStatusCode.PartialContent;
            response.Headers["Content-Range"] = "bytes " + startIndex + "-" + (startIndex + responseLength - 1) + "/" + fileLength;
        }

        response.Headers["Accept-Ranges"] = "bytes";
        response.Headers["Content-Length"] = responseLength.ToString();
        response.Cache.SetCacheability(HttpCacheability.Public); //required for etag output
        response.Cache.SetETag(etag); //required for IE9 resumable downloads
        response.ContentType = blob.Properties.ContentType;

        blob.DownloadRangeToStream(response.OutputStream, startIndex, responseLength);
    }
}

例子：

Response.AddHeader("Content-Disposition", "attachment; filename=" + filename); // force download
return new AzureBlobStream(blobContainerName, filename);

Answer 3

我注意到从 action 方法写入响应流会弄乱 HTTP 标头。缺少一些预期的标头，而其他标头设置不正确。

因此，我没有写入响应流，而是将 blob 内容作为流获取并将其传递给 Controller.File() 方法。

CloudBlockBlob blob = container.GetBlockBlobReference(blobName);
Stream blobStream = blob.OpenRead();
return File(blobStream, blob.Properties.ContentType, "FileName.txt");