This change makes it possible to publish multiple distributions
with packages named the same but with different content by changing
structure of the generated pool hierarchy. The option not enabled
by default as this changes the structure of the output which could
break the expectations of other tools.
While testing out Aptly, the `apt-get` client complains with the following error, since the `codename` was switched from the InRelease files that are baked out by Aptly:
```
E: Repository 'http://debianrepo.example.com/bionic testing InRelease' changed its 'Codename' value from '' to 'testing'
```
The added "aptly publish repo" option "-access-by-hash" publishes
the index files (Packages*, Sources*) also as hardlinked hashes.
Example:
/dists/yakkety/main/binary-amd64/by-hash/SHA512/31833ec39acc...
The Release files indicate this with the option "Acquire-By-Hash: yes"
This is used by apt >= 1.2.0 and prevents the "Hash sum mismatch" race
condition between a server side "aptly publish repo" and "apt-get update"
on a client.
See: http://www.chiark.greenend.org.uk/~cjwatson/blog/no-more-hash-sum-mismatch-errors.html
This implementation uses symlinks in the by-hash/*/ directory for keeping
only two versions of the index files and deleting older files
automatically.
Note: this only works with aptly.FileSystemPublishedStorage
Closes: #536
Signed-off-by: André Roth <neolynx@gmail.com>
Noa Resare
Steven Stone
Sjoerd Simons
Raúl Benencia
Stephan Eicher
Oliver Sauder
André Roth
Andrey Smirnov