Added: A site with a VarDir of its own can keep its logs, its INI cache and its expiry timestamps apart from the other sites of the installation

[fwoldt]

What changed

Installations that host several sites, each with a VarDir of its own, can now keep logs, caches and expiry
timestamps apart per site, or move them for all sites at once. Everything is set in site.ini [FileSettings], and
every default keeps today's behaviour.

Setting	Effect
UseGlobalLogDir=disabled	The debug logs (error.log, warning.log, …), the logs eZLog::write() writes to its default directory and the CSRF refusal log go to the log directory of the site (eZSys::logDirectory()) instead of var/log.
LogDir	May be an absolute path, as CacheDir already may. storage.log and the debug bar's log follow it.
LogVarDir, CacheVarDir	Put the logs or the caches of every site into a tree of their own with one line: the first directory of VarDir is replaced (var/example → var_log/example, var_cache/example). One memory file system can then hold the caches of all sites.
ExpiryDir	Keeps expiry.php outside the cache directory. With the cache on a memory file system, the expiry timestamps survive a restart. Otherwise image aliases created before a clear would count as current again.
INICacheDir=site	Caches the INI files of a site in its own cache directory, so clearing the INI cache of one site leaves the others alone.

Velocity and the web servers. Velocity serves the public caches below CacheVarDir (packed scripts and style
sheets, text to image) and nothing else there. expVelocity::staticPaths() adds them for all three engines, and only
for a plain relative directory name. .htaccess_root, .htaccess_root_static, the Apache example and the nginx
guide carry the matching rule, commented out, ready to enable.

Siteaccess changes. eZSiteAccess::change() derives the log directory, the INI cache directory and the expiry
file again on every change. This holds for web requests, REST, the tree menu and scripts (ezcache.php -s <siteaccess>, cronjobs). Nothing is kept in static properties:

• Velocity: a worker removes these globals between requests, so the next request starts with the defaults.
• Scripts: a process that changes siteaccess takes the paths of each site from its own site.ini.
• Multi-site wrappers: an INI cache directory a wrapper set before startup comes back for a site without the
  setting.

The guide doc/features/6.0/multi-site-log-and-cache-paths.md has sample setups (one site with its cache in memory;
many sites with one log tree and one cache tree), what each cache command clears, and the behaviour under Velocity.

New API:

• eZSys::logDirectory() and eZSys::relocatedVarDirectory()
• eZDebug::setLogDirectory() and logDirectory()
• eZExpiryHandler::filePath()
• eZSiteAccess::updateINICacheDirectory()
• eZUpdateDebugLogDirectory()
• expVelocity::staticPaths()

Why

Until now, multi-site hosting had to share more than the code:

• Logs: every site wrote its debug logs into the same var/log.
• INI cache: clearing the INI cache of one site removed it for all of them.
• Cache in memory: the only way was an absolute CacheDir, which site.ini calls unsupported. The files served
  from the cache would leave the served paths, and expiry.php would be lost at every restart.

How it was tested

New tests, all of which fail without the change:

• eZSiteLogAndExpiryPathsTest (14 tests, no database):
  • the log directory inside VarDir and absolute;
  • LogVarDir and CacheVarDir, relative and absolute;
  • the debug logs, eZLog and storage.log in the log directory;
  • UseGlobalLogDir;
  • ExpiryDir empty, relative, absolute and with a moved cache;
  • timestamps that survive an emptied cache directory.
• eZSiteAccessSitePathsTest (5 tests, writes temporary siteaccesses, no database):
  • eZSiteAccess::change() to a site with the settings and then to one without, in the same process;
  • the moved trees;
  • a directory the installation set, kept and restored;
  • a new request without the globals a Velocity worker removes.
• expVelocityEnginesTest: the public caches below CacheVarDir are served and nothing else there. An absolute path,
  .. or other characters are not served.

Existing suites: lib, kernel-classes and security give the same results as main.

Static checks: phpcs reports no new violations; phpstan reports nothing new in the changed files.

On an installation, with one siteaccess with the settings and one without, under nginx with PHP-FPM:

• Errors went to the log directory of the site with the settings, and to var/log for the other.
• The INI cache of the site with the settings was written to its own cache directory.
• ezcache.php -s <siteaccess> wrote the expiry timestamps to ExpiryDir.

Every cache command, cleared and purged (global_ini, ini, tag content, all caches):

• Each command removed only the cache it names.
• expiry.php in ExpiryDir was kept by every command and got the new timestamps.
• The .cleanup-trash directories were empty afterwards.

Multi-site layout: the global override set UseGlobalLogDir=disabled, LogVarDir=var_log,
CacheVarDir=var_cache, INICacheDir=site and ExpiryDir=expiry.

• Under nginx with PHP-FPM and under Velocity, pages linked their packed style sheets and scripts below
  var_cache/<site>/cache/public/ and got them (200).
• Other files there were refused (404).
• Errors went to var_log/<site>/log.
• Clearing and purging worked on var_cache, while expiry.php stayed in var/<site>/expiry/.

Velocity 0.0.4.45 (engine qbix, 4 persistent workers):

• 40 requests alternated between two siteaccesses, each worker serving both. All 20 errors of the one were in its log
  directory, all 20 of the other in var/log.
• 30 further requests to the site without the settings left the other site's INI cache untouched.

Still open

• Messages written before the siteaccess is known (while a request is matched) still go to var/log.
• A running Velocity holds settings in memory as before: after clearing an INI cache it needs a restart, as Setup >
  Caches says.
• Extensions that build a log path from VarDir and LogDir themselves do not follow LogVarDir. They should use
  eZSys::logDirectory().
• With a cluster file handler, the rewrite rules of index_cluster.php name var/ only. A moved cache would have to
  be added there.