Support for checksumAlgorithm

[miguelfteixeira]

While using checksumAlgorithm as part of the PutObjectRequest.builder() I've noticed that when I do a getObject operation using S3Mock not only I don't have access to the generated checksum (via response.response().checksumSHA256()) but also the response.contentEncoding is set to aws-chunked. Resulting in not being able to call ImageIO.read(response) when I call PutObject with checksumAlgorithm.

Everything works as expected when I remove the call to checksumAlgorithm or I use a real S3 Client, as in, response.contentEncoding is null and ImageIO.read(response) works.

It's the first I use this library and I've no experience with Kotlin (this is an existing project, I've just added the checksumAlgorithm). Is there any plans to provide support for this operation?

[afranken]

@miguelfteixeira checksums are indeed currently not supported in S3Mock.

it should be possible to add support in a future release, let me look into it.

[afranken]

Looked into this a bit.
First I thought that the S3 backend would need to calculate the checksum, but it's actually the client that calculates the checksum and then sends it to the backend - as part of the request body.

When uploading the sample file
ttps://github.com/adobe/S3Mock/blob/main/integration-tests/src/test/resources/sampleFile.txt

the body looks like this:

24
## sample test file ##

demo=content
0
x-amz-checksum-crc32:I6zdvg==

I'll have to test with more data to evaluate the pattern and build an inputstream similar to com.adobe.testing.s3mock.util.AwsChunkedDecodingInputStream where we skip the bytes we do not want to persist as binary data in the backend, and parse the checksum so we can return it in the API for later requests.