what's best way to check if a S3 object exists?

Currently, I make a Ge开发者_运维问答tObjectMetaDataRequest, if the GetObjectMetaDataResponse throw an exception means the object doesn't exist. Is there a better way to check whether the file exists without downloading the file.

you can use S3FileInfo class and Exists method of this class it will hep you to check if file exists without download the file .see the example below I used the AWSSDK 3.1.6 .net(3.5) :

public static  bool ExistsFile()
{
    BasicAWSCredentials basicCredentials = new BasicAWSCredentials("my access key", "my secretkey");
                AmazonS3Config configurationClient = new AmazonS3Config();
                configurationClient.RegionEndpoint = RegionEndpoint.EUCentral1;

                try
                {
                    using (AmazonS3Client clientConnection = new AmazonS3Client(basicCredentials, configurationClient))
                    {

                        S3FileInfo file = new S3FileInfo(clientConnection, "mybucket", "FolderNameUniTest680/FileNameUnitTest680");
                        return file.Exists;//if the file exists return true, in other case false
                    }
                }
                catch(Exception ex)
                {
                    return false;
                }
    }

Try this solution, it works for me.

AmazonS3Client client = new AmazonS3Client(accessKey, secretKey, regionEndpoint);       
S3FileInfo s3FileInfo = new S3FileInfo(client, bucketName, fileName);
return s3FileInfo.Exists;

If you are in a similar situation as myself and are using .Net Core and don't have access to Amazon.S3.IO (and S3FileInfo method), you can do the following using asynchronous GetObjectMetadataRequest method:

static private AmazonS3Client s3Client = new AmazonS3Client();

public static async Task<bool> FileExistsS3Async(string _bucket, string _key)
{
      GetObjectMetadataRequest request = new GetObjectMetadataRequest()
      {
            BucketName = _bucket,
            Key = _key
      };

      try
      {
            await s3Client.GetObjectMetadataAsync(request);
            return true;
      }
      catch (AmazonS3Exception exception)
      {
            return false;
      }
}

This function has worked for me when calling within a Unity game. You can also call the above function synchronously using the following:

bool exists = Task.Run(()=>FileExistsS3Async(_bucket, _key)).Result;

There is no ListObjectRequest, but instead a ListObjectsRequest where you cannot specify the Key. You then have to go through all the objects to find the one you want. I am currently looking in to it since I seem to get time out errors whilst downloading the file. (If anyone has some idea how to solve that feel free to comment).

You could instead try the List Parts Request if you happen to know the upload id.

Other than that I have no idea. Would like to have a chat with the person who wrote the S3 api...

You're probably going to have to use the REST API yourself, as the method suggested, internally just does exactly the same thing (try...catch on the request)

You can use this code to check whether an object exist in S3 or not:

public class S3CheckFileExists
{
    private readonly IAmazonS3 amazonS3;

    public S3CheckFileExists(IAmazonS3 amazonS3)
    {
        this.amazonS3 = amazonS3;
    }

    public async Task<bool> S3ObjectExists(string bucketName, string keyLocation)
    {
        var listS3Objects = await this.amazonS3.ListObjectsV2Async(new ListObjectsV2Request
        {
            BucketName = bucketName,
            Prefix = keyLocation, // eg myfolder/myimage.jpg (no / at start)
            MaxKeys = 1
        });

        if (listS3Objects.S3Objects.Any() == false || listS3Objects.S3Objects.All(x => x.Key != keyLocation))
        {
            // S3 object doesn't exist
            return false;
        }

        // S3 object exists
        return true;
    }
}

You'll need to register IAmazonS3 in your IoC (aka services) container though:

services.AddAWSService<IAmazonS3>();

Yes.

You can use a ListObjectsRequest. Use the Marker property, and retrieve only 1 element.