Add ability to check integrity of uploaded object

Hi Folks,

I've been reading https://aws.amazon.com/premiumsupport/knowledge-center/data-integrity-s3/ and I'm wondering whether s3fs could/does already support this functionality?

I've got a situation where I request a file from a data provider and in a separate request I can get the checksum of the file.

What I'd like to do is use s3fs to write the file and verify the integrity of the uploaded object by providing the checksum the data provider gives me, something like:

r = requests.get("a-url", stream=True)
if r.status_code == 200:
    try:
        with s3fs.open(f"<bucket-name>/object.type", "wb", md5checksum="ACHECKSUM") as file_out:
            shutil.copyfileobj(r.raw, file_out)
    except IntegrityError as ex:
        # Tidy up here

I've tried using the .checksum() function, but this doesn't return me the correct checksum, I can download the file and get the correct checksum with hashlib.md5().hexdigest(), so I know it's uploaded fine...

Appreciate any pointers you might have on this!

Start with the s3fs.open(..., "wb") upload path and the existing checksum() behavior, then review the AWS S3 data-integrity guidance linked in the issue. Define how a caller-supplied checksum should be checked during upload and what IntegrityError behavior should be observable, including cleanup after failure. Done means the requested flow verifies the uploaded object and has coverage for the checksum and failure cases.