Package: apt-cacher
Version: 1.7.4
Severity: wishlist
When downloading a package from the Debian archive aptitude keeps it in
the directory "/var/cache/apt/archives/partial". Upon completion the
file is then moved to the cache in "/var/cache/apt/archives" and then
installed. In case of network problems, or if the transfer is
interrupted for other reasons, the partial download is preserved. When
the file is needed again the download process is simply resumed with a
range request.
This instead is what happens, in chronological order, when the aptitude
client downloads the package from the apt-cacher proxy.
1. Download request on the client.
# aptitude -d install xulrunner-10.0-dbg
2. Processes started on the proxy host:
/usr/sbin/apt-cacher [inetd]
/usr/sbin/apt-cacher [libcurl]
/usr/sbin/apt-cacher [inetd]
[http://ftp.de.debian.org/debian/pool/main/i/iceweasel/libmozjs10d-dbg_10.0.6esr-1_amd64.deb]
File status on client:
-rw-r--r-- 1 root root 5643994 Aug 10 12:11
/var/cache/apt/archives/partial/libmozjs10d-dbg_10.0.6esr-1_amd64.deb
File status on the proxy:
-rw-r--r-- 1 www-data www-data 5643994 Aug 10 12:11
/var/cache/apt-cacher/packages/debian/libmozjs10d-dbg_10.0.6esr-1_amd64.deb
3. Network failure, the proxy has now no network connection to the Debian
mirror.
4. Wait some time to reach timeout. No apt-cacher processes are active any
longer.
File status on client:
-rw-r--r-- 1 root root 5646427 Jul 17 13:32
/var/cache/apt/archives/partial/libmozjs10d-dbg_10.0.6esr-1_amd64.deb
Note: the partial download has now the same time-stamp as the one in
the Debian mirror.
File status on proxy:
-rw-r--r-- 1 www-data www-data 5646427 Aug 10 12:13
/var/cache/apt-cacher/packages/debian/libmozjs10d-dbg_10.0.6esr-1_amd64.deb.corrupted
Note: the file name changed: ".corrupted" was added as extension.
5. The network connection starts working again after some time. The
proxy takes no autonomous actions.
6. Repeat download request on client,
# aptitude -d install xulrunner-10.0-dbg
aptitude wants to start from where it was forced to suspend:
3% [1 libmozjs10d-dbg 5,646 kB/17.2 MB 33%]
File status on client:
-rw-r--r-- 1 root root 5646426 Aug 10 12:19
/var/cache/apt-cacher/packages/debian/libmozjs10d-dbg_10.0.6esr-1_amd64.deb
Note: again a date change.
File status on proxy:
-rw-r--r-- 1 www-data www-data 1474249 Aug 10 12:19
/var/cache/apt-cacher/packages/debian/libmozjs10d-dbg_10.0.6esr-1_amd64.deb
-rw-r--r-- 1 www-data www-data 5646427 Aug 10 12:13
/var/cache/apt-cacher/packages/debian/libmozjs10d-dbg_10.0.6esr-1_amd64.deb.corrupted
The old file (with the ".corrupted" extension) is ignored. A new
file is opened and the package downloaded from the start.
7. On the client side aptitude waits in "stalled" status until
apt-cacher is reaching the size needed to satisfy its requested
range. The user has no idea about what is happening, will just read
the word "stalled" for some time and will probably think about a new
network failure, if it takes too long he will maybe simply quit
aptitude.
It would be more efficient if apt-cacher could simply resume suspended
downloads. It could, for example, rename the downloaded file to have a
".part" extension until the download is completed; if a client needs a
package that is not yet fully downloaded then apt-cacher should only get
the missing part with an HTTP range request.
To clean the archive from old and obsolete partially downloaded files
only the package version string should be used and not, of course, any
hash sum.
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