class ActiveStorage::Blob

def open(tmpdir: nil, &block)

Raises ActiveStorage::IntegrityError if the downloaded data does not match the blob's checksum.

The tempfile is automatically closed and unlinked after the given block is executed.

end
# ...
blob.open(tmpdir: "/path/to/tmp") do |file|

By default, the tempfile is created in Dir.tmpdir. Pass +tmpdir:+ to create it in a different directory:

The tempfile's name is prefixed with +ActiveStorage-+ and the blob's ID. Its extension matches that of the blob.

Downloads the blob to a tempfile on disk. Yields the tempfile. 
def open(tmpdir: nil, &block)
  service.open(
    key,
    checksum: checksum,
    verify: !composed,
    name: [ "ActiveStorage-#{id}-", filename.extension_with_delimiter ],
    tmpdir: tmpdir,
    &block
  )
end