下载大文件时浏览器崩溃

Question

我有一个 web api，它从 azure 读取文件并将其下载到字节数组中。客户端收到此字节数组并将其下载为 pdf。这不适用于大文件。 我无法弄清楚如何将字节从 web api 分块发送到客户端。

下面是web api代码，它只是将字节数组返回给客户端：

        CloudBlockBlob blockBlob = container.GetBlockBlobReference(fileName);
        blockBlob.FetchAttributes();
        byte[] data = new byte[blockBlob.Properties.Length];
        blockBlob.DownloadToByteArray(data, 0);
        return report;

客户端代码在ajax请求完成时获取数据，创建一个超链接并设置下载文件的下载属性：

var a = document.createElement("a");
a.href = 'data:application/pdf;base64,' + data.$value;;
a.setAttribute("download", filename);

1.86 MB 的文件出现错误。

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Answer 1

问题很可能是您的服务器在这些大文件上的内存不足。不要将整个文件加载到变量中，然后将其作为响应发送出去。这会导致双重下载，您的服务器必须从 azure 存储下载它并将其保存在内存中，然后您的客户端必须从服务器下载它。你可以做一个流来流复制，这样内存就不会被占用。这是来自您的 WebApi 控制器的示例。

public async Task<HttpResponseMessage> GetPdf()
{
    //normally us a using statement for streams, but if you use one here, the stream will be closed before your client downloads it.

    Stream stream;
    try
    {
        //container setup earlier in code

        var blockBlob = container.GetBlockBlobReference(fileName);

        stream = await blockBlob.OpenReadAsync();

        //Set your response as the stream content from Azure Storage
        response.Content = new StreamContent(stream);
        response.Content.Headers.ContentLength = stream.Length;

        //This could change based on your file type
        response.Content.Headers.ContentType = new MediaTypeHeaderValue("application/pdf");
    }
    catch (HttpException ex)
    {
        //A network error between your server and Azure storage
        return this.Request.CreateErrorResponse((HttpStatusCode)ex.GetHttpCode(), ex.Message);
    }
    catch (StorageException ex)
    {
        //An Azure storage exception
        return this.Request.CreateErrorResponse((HttpStatusCode)ex.RequestInformation.HttpStatusCode, "Error getting the requested file.");
    }
    catch (Exception ex)
    {
        //catch all exception...log this, but don't bleed the exception to the client
        return this.Request.CreateErrorResponse(HttpStatusCode.BadRequest, "Bad Request");
    }
    finally
    {
        stream = null;
    }
}

我已经（几乎完全）使用了这段代码，并且能够下载超过 1GB 大小的文件。