如何直接从Amazon s3存储中提供非公共文件

Question

We need to work on .net based web application that will upload files to Amazon S3 Storage bucket using admin panel of the app and clients will be given to downloadable files with client.aspx file.

We looked at few example and got confused with some of the sample code for downloading non public files from S3 storage. one such example is below

AmazonS3Config config = new AmazonS3Config()
{
RegionEndpoint = RegionEndpoint.USEast1
};
IAmazonS3 client = new AmazonS3Client(accessKey, secretKey, config);
string dest = System.IO.Path.GetTempPath() + "event.mp4";
using (client)
{
GetObjectRequest request = new GetObjectRequest() { BucketName = "bucketname" + @"/" + "videos2015", Key = "event.mp4" };
using (GetObjectResponse response = client.GetObject(request))
{
response.WriteResponseStreamToFile(dest);
}
}
Response.Clear();
Response.AppendHeader("content-disposition", "attachment; filename=" + "dynamic_filename.png");
Response.ContentType = "application/octet-stream";
Response.TransmitFile(dest);
Response.Flush();
Response.End();

When user click on the link following code gets executed on web server and code downloads file on the web server and then serves the same file to client... if i am not wrong. Is there not a way that we can serve file for download directly from the AWS S3 storage.

In above case it is waste of server resources and increases the download time also.

Out files on AWS are not Public they are non public so the url is not accessible directly from client browsers as is in case of public content type

Answer 1

The pre-signed urls are indeed what you are looking for. Since you are using C#, here is a link to some useful code examples:

http://docs.aws.amazon.com/AmazonS3/latest/dev/ShareObjectPreSignedURLDotNetSDK.html

There is no need to upload files to s3 thru your webserver, they can be sent directly. Same thing on the download, download directly from S3 - don't copy them to EC2 first, you would be wasting bandwidth and processing resources.

Answer 2

You can use Minio-dotnet client library Its Open Source & supports compatible S3 API.

Here is an example for PresignedPostPolicy

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Minio;

namespace Minio.Examples
{
    class PresignedPostPolicy
    {
        static int Main()
        {
          /// Note: YOUR-ACCESSKEYID, YOUR-SECRETACCESSKEY, my-bucketname and
          /// my-objectname are dummy values, please replace them with original values.
            var client = new MinioClient("s3.amazonaws.com", "YOUR-ACCESSKEYID", "YOUR-SECRETACCESSKEY");
            PostPolicy form = new PostPolicy();
            DateTime expiration = DateTime.UtcNow;
            form.SetExpires(expiration.AddDays(10));
            form.SetKey("my-objectname");
            form.SetBucket("my-bucketname");

            Dictionary <string, string> formData = client.PresignedPostPolicy(form);
            string curlCommand = "curl ";
            foreach (KeyValuePair<string, string> pair in formData)
            {
                    curlCommand = curlCommand + " -F " + pair.Key + "=" + pair.Value;
            }
            curlCommand = curlCommand + " -F file=@/etc/bashrc https://s3.amazonaws.com/my-bucketname";
            Console.Out.WriteLine(curlCommand);
            return 0;
        }
    }
}

And below one for PresignedPutObject

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Minio;

namespace Minio.Examples
{
    class PresignedPutObject
    {
        static int Main()
        {
          /// Note: YOUR-ACCESSKEYID, YOUR-SECRETACCESSKEY, my-bucketname and
          /// my-objectname are dummy values, please replace them with original values.
            var client = new MinioClient("s3.amazonaws.com", "YOUR-ACCESSKEYID", "YOUR-SECRETACCESSKEY");
            Console.Out.WriteLine(client.PresignedPutObject("my-bucketname", "my-objectname", 1000));
            return 0;
        }
    }
}

Hope it helps.

PS: I work for Minio