AWS .NET SDK 直接上传到 S3 - 预签名 URL

Question

我试图了解用于将文件上传到 S3 的特定 .NET SDK 示例 (seen here) 是先上传到我的服务器，还是直接上传到 S3？

我怀疑文件首先上传到我的服务器，然后保存到 S3。但也许 SDK 会神奇地绕过我的服务器？代码如下：

using System;
using System.IO;
using System.Net;
using Amazon.S3;
using Amazon.S3.Model;

namespace s3.amazon.com.docsamples
{
    class UploadObjcetUsingPresignedURL
    {
        static IAmazonS3 s3Client;
        // File to upload.
        static string filePath   = "*** Specify file to upload ***";
        // Information to generate pre-signed object URL.
        static string bucketName = "*** Provide bucket name ***";
        static string objectKey  = "*** Provide object key for the new object ***";

        public static void Main(string[] args)
        {
            try
            {
                using (s3Client = new AmazonS3Client(Amazon.RegionEndpoint.USEast1))
                {
                    string url = GeneratePreSignedURL();
                    UploadObject(url);

                }
            }
            catch (AmazonS3Exception amazonS3Exception)
            {
                if (amazonS3Exception.ErrorCode != null &&
                    (amazonS3Exception.ErrorCode.Equals("InvalidAccessKeyId")
                    ||
                    amazonS3Exception.ErrorCode.Equals("InvalidSecurity")))
                {
                    Console.WriteLine("Check the provided AWS Credentials.");
                    Console.WriteLine(
                    "To sign up for service, go to http://aws.amazon.com/s3");
                }
                else
                {
                    Console.WriteLine(
                     "Error occurred. Message:'{0}' when listing objects",
                     amazonS3Exception.Message);
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
            Console.WriteLine("Press any key to continue...");
            Console.ReadKey();
        }


        static void UploadObject(string url)
        {
            HttpWebRequest httpRequest = WebRequest.Create(url) as HttpWebRequest;
            httpRequest.Method = "PUT";
            using (Stream dataStream = httpRequest.GetRequestStream())
            {
                byte[] buffer = new byte[8000];
                using (FileStream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read))
                {
                    int bytesRead = 0;
                    while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) > 0)
                    {
                        dataStream.Write(buffer, 0, bytesRead);
                    }
                }
            }

            HttpWebResponse response = httpRequest.GetResponse() as HttpWebResponse;
        }

        static string GeneratePreSignedURL()
        {
            GetPreSignedUrlRequest request = new GetPreSignedUrlRequest
                {
                    BucketName = bucketName,
                    Key        = objectKey,
                    Verb       = HttpVerb.PUT,
                    Expires    = DateTime.Now.AddMinutes(5)
                };

            string url = null;
            url = s3Client.GetPreSignedURL(request);
            return url;
        }
    }
}

问题又来了
上面的例子是不是先上传到服务器，再传文件到S3？还是以某种方式绕过服务器并直接上传到 S3？

谢谢！

编辑
正如 TJ 所说，答案是肯定的，它会在到达亚马逊之前先通过我的服务器。现在感觉有点像一个愚蠢的问题。

如果有人感兴趣，我决定使用带有预签名 URL 的 CORS AJAX 上传到 S3。起初相当复杂，但我现在可以正常工作了。因此，我的服务器可以高枕无忧，同时进行无数次上传！

Answer 1

就是这一行：

while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) > 0)

在写入输出流之前，字节会被读入您的服务器（不保存在磁盘上，而是保留在内存中）。因此，您的服务器不会被绕过。