S3 Client not Exposing HeadBucket

[dscpinheiro]

Discussed in #3175

^{Originally posted by omamoo February 7, 2024}
Hello all,

I'm writing a code that uploading content to S3 bucket that resides at different account, i.e. I have a cross account scenario of uploading content to S3.

While writing the code I used GetBucketLocation API call to determine the bucket location, however on cross account scenario the GetBucketLocation fails since I'm not the bucket owner, in addition, I saw on AWS documentation that their recommendation is to use HeadBucket API call, however the SDK does not expose this API call and defined this call as internal.

Here is a snapshot from the SDK code:

internal virtual Task<HeadBucketResponse> HeadBucketAsync(HeadBucketRequest request, System.Threading.CancellationToken cancellationToken = default(CancellationToken))
        {
            var options = new InvokeOptions();
            options.RequestMarshaller = HeadBucketRequestMarshaller.Instance;
            options.ResponseUnmarshaller = HeadBucketResponseUnmarshaller.Instance;

            return InvokeAsync<HeadBucketResponse>(request, options, cancellationToken);
        }

Can we make this public for use?

[b-dongen]

In case anyone is inpatient like me, I've created this extension method using reflection to access the HeadBucketAsync() method.

`static class AmazonS3ClientExtension
{
#pragma warning disable S3011 // Reflection should not be used to increase accessibility of classes, methods, or fields
static readonly MethodInfo _headBucketAsyncMethod = typeof(AmazonS3Client)
.GetMethod("HeadBucketAsync", BindingFlags.Instance | BindingFlags.NonPublic)!;
static readonly FieldInfo _httpClientResponseDataHeaderField = typeof(HttpClientResponseData)
.GetField("_headers", BindingFlags.NonPublic | BindingFlags.Instance)!;
#pragma warning restore S3011 // Reflection should not be used to increase accessibility of classes, methods, or fields

static public Task<HeadBucketResponse> HeadBucketAsync(this AmazonS3Client client, HeadBucketRequest request, CancellationToken cancellationToken = default)
    => (Task<HeadBucketResponse>)_headBucketAsyncMethod.Invoke(client, [request, cancellationToken])!;

// Use reflection to get the region from the response-headers
static public string? GetRegionFromResponseHeader(this AmazonServiceException ex)
{
    var responseEx = ex.InnerException as HttpErrorResponseException;
    var responseData = responseEx?.Response as HttpClientResponseData;
    var headers = _httpClientResponseDataHeaderField.GetValue(responseData) as Dictionary<string, string>;
    string? region = headers?.GetValueOrDefault("x-amz-bucket-region");

    return region;
}

}`