The downloaded file is different from the uploaded one

[ImoutoChan]

Describe the bug

Our tests are failing after updating from version 3.7.410.1 to 3.7.412.4 because the stream returned by GetObjectAsync differs from the one provided to PutObjectAsync.

Uploading

var request = new PutObjectRequest
{
    BucketName = bucketName,
    Key = key,
    InputStream = inputStream
};

await _client.PutObjectAsync(request, ct);

Download

var request = new GetObjectRequest
{
    BucketName = bucketName,
    Key = key
};

var response = await _client.GetObjectAsync(request, ct);
return response.ResponseStream;

Before the update, response.ResponseStream and inputStream were identical (verified via MD5 hashes). After the update, they are different.

Regression Issue

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

Expected Behavior

The response stream from GetObjectAsync returns the exact bytes provided in the inputStream.

Current Behavior

The streams are different.

Reproduction Steps

Above

Possible Solution

No response

Additional Information/Context

No response

AWS .NET SDK and/or Package version used

3.7.410.1
3.7.412.4

Targeted .NET Platform

net 9.0

Operating System and version

win10

[dscpinheiro]

Can you share how you're verifying the MD5 hashes? We made a change recently to automatically calculate checksums (#3610), but we didn't modify the SDK's MD5 implementation at all.

Also, are you using actual S3 or a 3rd-party implementation?

[dscpinheiro]

For example, I just tested with the latest version of the S3 package and this returned the correct MD5 hash (CryptoUtilFactory is available in the Amazon.Util namespace):

var s3Client = new AmazonS3Client(RegionEndpoint.USWest2);
var inputStream = new FileStream("test-file.pdf", FileMode.Open);
var inputMD5 = Convert.ToBase64String(CryptoUtilFactory.CryptoInstance.ComputeMD5Hash(inputStream));

var putResponse = await s3Client.PutObjectAsync(new PutObjectRequest
{
    BucketName = "dspin-test",
    Key = "test.pdf",
    InputStream = inputStream
});

var getResponse = await s3Client.GetObjectAsync(new GetObjectRequest
{
    BucketName = "dspin-test",
    Key = "test.pdf"
});

var outputMD5 = Convert.ToBase64String(CryptoUtilFactory.CryptoInstance.ComputeMD5Hash(getResponse.ResponseStream));
Console.WriteLine(inputMD5 == outputMD5); // Outputs "True"

[ImoutoChan]

I'm calculating the MD5 hashes myself in tests:

public static string GetMd5Hash(this byte[] bytes)
{
    var computed = MD5.HashData(bytes);
    return BitConverter.ToString(computed).Replace("-", "").ToLower();
}

public static string GetMd5Hash(this Stream stream)
{
    using var md5 = MD5.Create();
    var computed = md5.ComputeHash(stream);
    return BitConverter.ToString(computed).Replace("-", "").ToLower();
}

Also, are you using actual S3 or a 3rd-party implementation?

Yes, I'm using a third-party implementation

[dscpinheiro]

Got it. As mentioned in the announcement I linked earlier, the change was made intentionally but there's a config option you can set to prevent the SDK from calculating checksums (for PutObject calls):

var s3Config = new AmazonS3Config
{
    ServiceURL = "your-custom-service-url",
    RequestChecksumCalculation = RequestChecksumCalculation.WHEN_REQUIRED,
};
var s3 = new AmazonS3Client(s3Config);
await s3.PutObjectAsync(...);

Can you try that and let me know if it works? If possible, could you also share which 3rd-party implementation you're using?

[ImoutoChan]

Thank you, that option fixed the behavior!

We’re using a local cloud provider: https://s3.ru-1.storage.selcloud.ru/, which claims full compatibility with the S3 API. However, I suspect they have not yet implemented the latest feature.

[dscpinheiro]

Glad it worked for you! And yes, unfortunately after we made this change (which was already available - not by default - for S3 since 2022 - https://aws.amazon.com/blogs/aws/new-additional-checksum-algorithms-for-amazon-s3/), some 3rd-party implementations stopped working.

The config options can be used but obviously the ideal solution would be for the 3rd-party implementations to support this new behavior as it's in place for all AWS SDKs - not only .NET (this documentation page from S3 explains how the data integrity works in more detail: https://docs.aws.amazon.com/AmazonS3/latest/userguide/checking-object-integrity.html)

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