Unexpected file upload updating unrelated column

[xanderman]

I have a model with an uploader mounted on remote_document, and code that downloads the file to do a virus scan on it. The code looks roughly like this:

# I can't figure out a better way to download the file locally and check that it worked. Open to suggestions.
cache = document.remote_document.cache!
if cache.nil?
  Rails.logger.warn("download failed")
  document.update(virus_scan_result: :error)
  return
end

path = document.remote_document.file.file
result = ClamScan::Client.scan(location: path)
document.update(virus_scan_result: result.status)

In our S3 logs we noticed unexpected PUT requests, apparently uploading new versions of files. I dug into spans in datadog and was shocked to discover that there is a PUT happening as part of the transaction in this code (I think it's the "happy path" based on logging). The only thing I can guess is that carrierwave's callback decided that the file was modified. Why would there be an upload here? I'm not even updating the remote_document column.

[mrkgrandjean]

Any Update on this? I believe I am seeing this behavior as well.

[chamnap]

I'm seeing this behavior too well. Hope it gets resolved soon.

[xanderman]

FYI, I have a hacky "solution" that appears to be working. At least, looking at recent traces from the virus scan job, I'm not seeing PUT requests anymore. The solution is to skip callbacks on the record update by using a different method:

document.update(virus_scan_result: result.status)

becomes

document.update_column(:virus_scan_result, result.status)

Skipping callbacks comes with a mountain of caveats, of course, and isn't ideal. But at least it's preventing the unexpected PUT.

For completeness, before skipping callbacks I also tried copying the file to a new location before running the virus scanner on it. My guess was that the scan was touching the file in some way and carrierwave was picking up the modification and saving the file. It didn't help; we still saw the PUT requests. I have no theory right now for why we see the unexpected upload.