Two-thirds of the way through a substantial bulk upload of objects to S3 I realized I had forgotten to add a header to the objects I was uploading. Specifically, I wanted each object to have a Content-Disposition header to coax browsers into saving objects with a specific filename rather than displaying them inline or saving them with the long, unwieldy key name that had been generated for the objects.

I certainly wouldn’t want to upload the files all over again just to add a header. Thankfully it’s easy enough to add the header without resending the content of the file by simply moving the key onto itself, i.e., move the object but let the source key and the destination key be identical. Using the right_aws gem this is accomplished easily enough:

  BUCKET_NAME, "foo.txt", # source bucket and key
  BUCKET_NAME, "foo.txt", # destination bucket and key
  'Content-Disposition'=>'attachment; filename="bar.txt"')

The above snippet adds a Content-Disposition header to the object with key foo.txt. Browsers respecting the Content-Disposition header would try to download the file and save it with the name bar.txt rather than trying to display it inline. This comes in handy if your key names tend to run long because you must embed additional information in them but would rather the user did not have put up with that when downloading the object.