Librarian-backed HostedFile objects do not expose hash

Here's some code from lib/lp/soyuz/scripts/queue.py, which I'm trying to replace with an API client:

                    # Check sha against existing file (bug #67014)
                    existing_sha = hashlib.sha1()
                    for chunk in filechunks(existing_file):
                        existing_sha.update(chunk)
                    existing_file.close()

                    # bail out if the sha1 differs
                    if libfile.content.sha1 != existing_sha.hexdigest():
                        raise CommandRunnerError("%s already present on disk "
                                                 "and differs from new file"
                                                 % libfile.filename)
                    else:
                        self.display("%s already on disk and checksum "
                                     "matches, skipping.")

As far as I can see, it's not possible to do a like-for-like replacement of this, because the HostedFile objects that you get on webservice clients if you export something as Bytes() don't expose LibraryFileContent.sha1 anywhere; so in order to check whether a file you already have on disk matches the one in the librarian, you have to download the librarian's copy and compare it directly. In the case at hand, a common source of filename collisions that would reach this code is *.orig.tar.* files, and those are often very large (tens or hundreds of megabytes).

It would be great if HostedFile objects (not HostedFileBuffer - constructing those requires downloading the value) exported the SHA-1 so that I could write a direct equivalent of the code above.