V4 Initial Feedback

[niemyjski]

Describe the bug

I'd consider this a bug and hopefully addressed quickly. It's against the .NET Framework guidelines to return null for collections. There was a ton of breaking tests for my project because I'm not yet targeting NRT (netstandard 2.0).

https://learn.microsoft.com/en-us/dotnet/standard/design-guidelines/guidelines-for-collections

❌ DO NOT return null values from collection properties or from methods returning collections. Return an empty collection or an empty array instead.

Also I noticed that there was very little docs on migration to STJ. I converted it fine, but considering I'm messing with ReDrive Headers it would be nice if there were strongly typed models for this.

Regression Issue

• Select this option if this issue appears to be a regression.

Expected Behavior

Be Idiomatic to the platform you are targeting.

Current Behavior

3.7 works as expected.

Reproduction Steps

upgrade to 4, watch your app break majorly. This wasn't even in the 4.0 release notes.

Possible Solution

No response

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

4.0.0

Targeted .NET Platform

netstandard 2.0

Operating System and version

macos

[niemyjski]

Like this does not seem like good dx... Here is a sample from our code:

        var deleteRequest = new DeleteObjectsRequest { BucketName = _bucket };

        ListObjectsV2Response listResponse;
        do
        {
            listResponse = await _client.ListObjectsV2Async(listRequest, cancellationToken).AnyContext();
            listRequest.ContinuationToken = listResponse.NextContinuationToken;

            var keys = listResponse.S3Objects?.MatchesPattern(criteria.Pattern).Select(o => new KeyVersion { Key = o.Key }).ToArray();
            if (keys is not { Length: > 0 }) // New Null check above and had to change this.
                continue;

            deleteRequest.Objects.AddRange(keys); // <--- NRE because you now have to new up EVERYthing

[dscpinheiro]

We know this was a contentious change, but the V4 blog posts have more background on why this decision was made.

From the GA announcement:

As described in the migration guide, collection properties for types used for requests and responses to AWS services default to null instead of an empty collection as was done in V3. This change was implemented for performance and to allow the SDK and consumers of the SDK to distinguish between the state of a property not being set versus the property being set to an empty collection. The preview 1 blog post dives more deeply into the performance benefits of this change.

And the first preview announcement:

In V3, properties of type List or Dictionary for requests and responses types were initialized to an empty collection. When making requests, the SDK would only send the property if the collection was not empty. This was done to avoid null pointer exceptions in code using the SDK but it has the following drawbacks:

• The SDK couldn’t always understand the user’s intent, especially when attempting to clear out a collection on an AWS resource.
• When getting a response back from a service, users couldn’t tell if the empty collection was due to the default initialization of the SDK or if the service actual sent back an empty collection.
• Collections were being created that were not even being used, which caused wasted allocations.

We also added a new config option (Amazon.AWSConfigs.InitializeCollections) that can be set to true to change the runtime behavior to be the same as in V3. This can be used if you don't want to refactor all code using collections but still leverage the other performance improvements included in V4.

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For the other comment related to System.Text.Json, that should be transparent for customers. If there's a specific regression you're running into, please open a new issue and we'll take a look.

[niemyjski]

I appreciate taking the time to post this and I'll check those out. I think it would be great to post this in a github change log or release notes (bottom of). I don't check blogs for this kind of thing (most are just from marketing anyways??) or contain 80 other technologies I don't even need to consume brain cycles with.. I look at the nuget packages and go straight to the github release notes as that should be the source of truth.

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