如何从 S3 获取 GetObjectResponse 的字节？答案

【问题标题】：How can I get the bytes of a GetObjectResponse from S3?如何从 S3 获取 GetObjectResponse 的字节？
【发布时间】：2016-03-12 16:48:47
【问题描述】：

我正在从 Amazon S3 检索文件。我想将文件转换为字节，以便我可以按如下方式下载它：

var download = new FileContentResult(bytes, "application/pdf");
download.FileDownloadName = filename;
return download;

我这里有文件：

var client = Amazon.AWSClientFactory.CreateAmazonS3Client(
        accessKey,
        secretKey,
        config
        );
GetObjectRequest request = new GetObjectRequest();
GetObjectResponse response = client.GetObject(request);

我知道 response.WriteResponseStreamToFile() 但我想将文件下载到常规下载文件夹。如果我将 GetObjectResponse 转换为字节，我可以返回该文件。我该怎么做？

【问题讨论】：

标签： c# amazon-web-services amazon-s3 download byte

【解决方案1】：

这是我为其他需要它的人找到的解决方案：

GetObjectResponse response = client.GetObject(request);
using (Stream responseStream = response.ResponseStream)
{
    var bytes = ReadStream(responseStream);
    var download = new FileContentResult(bytes, "application/pdf");
    download.FileDownloadName = filename;
    return download;
}

public static byte[] ReadStream(Stream responseStream)
{
    byte[] buffer = new byte[16 * 1024];
    using (MemoryStream ms = new MemoryStream())
    {
        int read;
        while ((read = responseStream.Read(buffer, 0, buffer.Length)) > 0)
        {
            ms.Write(buffer, 0, read);
        }
        return ms.ToArray();
    }
}

【讨论】：

【解决方案2】：

只是另一种选择：

Stream rs;    
using (IAmazonS3 client = Amazon.AWSClientFactory.CreateAmazonS3Client())
{
    GetObjectRequest getObjectRequest = new GetObjectRequest();
    getObjectRequest.BucketName = "mybucketname";
    getObjectRequest.Key = "mykey";

    using (var getObjectResponse = client.GetObject(getObjectRequest))
    {
              getObjectResponse.ResponseStream.CopyTo(rs);
    }
}

【讨论】：

'ResponseStream.CopyTo' 比在其他答案中必须创建方法'ReadStream(Stream responseStream)' 更干净。您也可以使用“CopyToAsync”并使方法异步。

【解决方案3】：

我努力让 Alex 提供的更清洁的方法起作用（不确定我缺少什么），但我想不使用 Erica 提供的额外 ReadStream 方法（尽管它有效）......在这里这就是我最终要做的事情：

var s3Client = new AmazonS3Client(AccessKeyId, SecretKey, Amazon.RegionEndpoint.USEast1);
    using (s3Client)
    {
        MemoryStream ms = new MemoryStream();
        GetObjectRequest getObjectRequest = new GetObjectRequest();
        getObjectRequest.BucketName = BucketName;
        getObjectRequest.Key = awsFileKey;

        using (var getObjectResponse = s3Client.GetObject(getObjectRequest))
        {
            getObjectResponse.ResponseStream.CopyTo(ms);
        }
        var download = new FileContentResult(ms.ToArray(), "image/png"); //"application/pdf"
        download.FileDownloadName = ToFilePath;
        return download;
    }

【讨论】：

【解决方案4】：

Stream 现在有异步方法。在 C# 8 中，您可以这样做：

public async Task<byte[]> GetAttachmentAsync(string objectPointer)
{
    var objReq = new GetObjectRequest
    {
        BucketName = "bucket-name",
        Key = objectPointer,    // the file name
    };

    using var objResp = await _s3Client.GetObjectAsync(objReq);
    using var ms = new MemoryStream();
    await objResp.ResponseStream.CopyToAsync(ms, _ct);  // _ct is a CancellationToken
    return ms.ToArray();
}

这不会在 IO 发生时阻塞任何线程。

【讨论】：

当我从同步方法调用它时，我对它的行为方式有点困惑。