Comment 7 for bug 1699396

Dupped my bug onto this.
Carrying some info from there:

1. this is essentially a re-occurrence of bug 1668876

2. another way to repro:
$ uvt-simplestreams-libvirt --verbose sync --source http://cloud-images.ubuntu.com/daily arch=amd64 label=daily release=xenial
[...]
    raise checksum_util.invalid_checksum_for_reader(self)
simplestreams.checksum_util.InvalidChecksum: Invalid sha256 Checksum at http://cloud-images.ubuntu.com/daily/server/xenial/20170620/xenial-server-cloudimg-amd64-disk1.img. Found 9fc24ce8113fc635567a3944ccb518d3c09bd9270315f3d654811db7221391d1. Expected bb5e963ece5c1f6071436470dbc09955a9227ce51d47636ffcf43dab60605ddf. read 287506432 bytes expected 146210816 bytes. (size 287506432 expected 146210816)

3. in the old bug we had a test to check all images published, that executed lists all xenial arch/types as broken (see file attached to the dup bug 1699454)

Other than fixing the images, you should consider running a checker (maybe local to the publishing machine for speed) of images vs checksums file - almost on a 5 minute schedule or such and auto-bug you if it fails. Would that be reasonable?