Mirror update repeats download exists file

[MSI77]

Detailed Description

Always repeats download exist files after download error.

Context

aptly mirror create -architectures="i386,amd64" -with-udebs=true xenial-main https://mirror.yandex.ru/ubuntu/ xenial main
aptly mirror update xenial-main

ERROR: unable to update: download errors:
https://mirror.yandex.ru/ubuntu/pool/main/l/language-pack-gnome-mn/language-pack-gnome-mn_16.04+20160320_all.deb: unexpected EOF
https://mirror.yandex.ru/ubuntu/pool/main/liba/libabw/libabw-0.1-1v5_0.1.1-2ubuntu2_i386.deb: unexpected EOF
https://mirror.yandex.ru/ubuntu/pool/main/t/taglib/libtag1v5-vanilla_1.9.1-2.4ubuntu1_amd64.deb: unexpected EOF
https://mirror.yandex.ru/ubuntu/pool/main/w/whoopsie-preferences/libwhoopsie-preferences-dev_0.18_i386.deb: Get https:/ubuntu/pool/main/w/whoopsie-preferences/libwhoopsie-preferences-dev_0.18_i386.deb: dial tcp 213.180.204.183:443: i/o timeout
https://mirror.yandex.ru/ubuntu/pool/main/p/psycopg2/python-psycopg2-dbg_2.6.1-1build2_i386.deb: unexpected EOF
https://mirror.yandex.ru/ubuntu/pool/main/liba/libassuan/libassuan-dev_2.4.2-2_amd64.deb: unexpected EOF

Always download full repo.

[erickeller]

I suspect this is a duplicate of #641

[exaos]

The same error here. After downloading ~80GB packages, aptly mirror update stopped with an "I/O timeout" error. Then, I restart the mirror updating and hope it will continue to finish the remaining downloading. Unfortunately, aptly starts to download from the scratch. After failure twice, my mirror keeps this status ("Last update: never") but with a pool around 160GB which I don't know how to use.
(Aptly 1.1.1 on Archlinux.)
Are there any way to just download the only missing packages while the mirror updating is interrupted and restarted?

[smira]

Yep, I believe it's same as #641. I'll try to get it fixed for the next version

[dpvpro]

I confirm this case.

[smira]

Should be available now in nightly aptly_1.1.1+75+g9cb2a30