C# SDK: How to determine if GetObjectAsync succeeded?

[petertiedemann]

When accessing an object with a key that does not exist, the stream provided by GetObjectAsync contains an XML error and does not throw and error when read, How should a caller avoid returning this XML error string in place of an actual string? I realize it is possible to call StatObjectAsync first, but that raises concerns about what happens if stat is called first, then before getobject a remove call is made.

Expected Behavior

I would expect an exception from GetObjectAsync if the object could not be retrieved.

Current Behavior

The stream contains an XML string:

<?xml version="1.0" encoding="UTF-8"?>
<Error><Code>NoSuchKey</Code><Message>The specified key does not exist.</Message><Resource>/storagetest.f7f3da7a3a0b4ff299794b47161dccf6/Key Not Found</Resource><RequestId>15704FE60F942D64</RequestId><HostId>3L137</HostId></Error>

Possible Solution

• Provide a separate callback for the missing object scenario
• Provide a null stream
• Throw an exception

Steps to Reproduce (for bugs)

Call GetObjectAsync and provide a non-existing object key.

Context

I am concerned about concurrency problems with remove operations.

Your Environment

• Version used (minio version): 2018-12-13T02:04:19Z
• Environment name and version (e.g. nginx 1.9.1): n/a
• Server type and version: n/a
• Operating System and version (uname -a): Windows 10
• Link to your project: n/a

[petertiedemann]

Looking at the other SDKs, i see its the same in Java, but in Go statObject is not suggested, so i assume the returned error would indicate that the object was not found?

[poornas]

@petertiedemann, minio-dotnet does a StatObject internally - I see a ObjectNotFoundException when GetObjectAsync is attempted on a non-existent object

 await minio.GetObjectAsync("tbucket", objectName, 
 (stream) =>
 {
      // Uncommment to print the file on output console
      // stream.CopyTo(Console.OpenStandardOutput());
 });

Cases/GetBucketNotification.cs(36,30): warning CS0168: The variable 'e' is declared but never used [/home/kris/code/minio-dotnet/Minio.Examples/Minio.Examples.csproj]
Running example for API: GetObjectAsync
[Bucket]  Exception: minio-dotnet-example-shzw2: Not found.: Minio.Exceptions.ObjectNotFoundException: Minio API responded with message=Not found.
   at Minio.MinioClient.ParseError(IRestResponse response) in /home/kris/code/minio-dotnet/Minio/MinioClient.cs:line 447
   at Minio.MinioClient.<>c.<.ctor>b__77_0(IRestResponse response) in /home/kris/code/minio-dotnet/Minio/MinioClient.cs:line 71
   at Minio.MinioClient.HandleIfErrorResponse(IRestResponse response, IEnumerable`1 handlers, DateTime startTime) in /home/kris/code/minio-dotnet/Minio/MinioClient.cs:line 503
   at Minio.MinioClient.ExecuteTaskAsync(IEnumerable`1 errorHandlers, IRestRequest request, CancellationToken cancellationToken) in /home/kris/code/minio-dotnet/Minio/MinioClient.cs:line 350
   at Minio.MinioClient.GetObjectAsync(String bucketName, String objectName, Action`1 cb, ServerSideEncryption sse, CancellationToken cancellationToken) in /home/kris/code/minio-dotnet/Minio/ApiEndpoints/ObjectOperations.cs:line 63
   at Minio.Examples.Cases.GetObject.Run(MinioClient minio, String bucketName, String objectName, String fileName) in /home/kris/code/minio-dotnet/Minio.Examples/Cases/GetObject.cs:line 34

[poornas]

ok, I see a bug in this GetObjectAsync api call where we are not doing a stat prior to fetching - will fix it.

 public async Task GetObjectAsync(string bucketName, string objectName, long offset, long length, Action<Stream> cb, ServerSideEncryption sse = null,CancellationToken cancellationToken = default(CancellationToken))

The other API call should work -

 public async Task GetObjectAsync(string bucketName, string objectName, string fileName,ServerSideEncryption sse = null, CancellationToken cancellationToken = default(CancellationToken))

[petertiedemann]

@poornas Thanks for the super prompt responses, and especially the follow-up answer because i thought i had gone crazy because suddenly i was getting the exception (because i was trying a different overload i guess :)

Btw, the overload with ServerSideEncryption is not present in the nuget i am using it seems? ( i am using Minio 2.0.6 on .net standard 2.0 )

[poornas]

@petertiedemann, the serverside encryption feature is still in review #259, after merging that to master we would make a release

[petertiedemann]

Ah okay, thanks. Just got worried if I was on the wrong version. Minio is looking really good so far.

[nitisht]

fixed by #260