The code is easier to maintain in an actual JavaScript file.
Especially with how variables were declared and concatenated in
a different order.
Change-Id: I758acb78de1cdf2128e81c86f992807ef0dbf444
This greatly simplifies logic required to compute module versions.
It also makes it significantly less error-prone.
Since f37cee996e, we support hashes as versions (instead of timestamps).
This means we can build a hash of the content directly, instead of compiling a
large array with all values that may influence the module content somehow.
Benefits:
* Remove all methods and logic related to querying database and disk for
timestamps, revision numbers, definition summaries, cache epochs, and more.
* No longer needlessly invalidate cache as a result of no-op changes to
implementation datails. Due to inclusion of absolute file paths in the
definition summary, cache was always invalidated when moving wikis to newer
MediaWiki branches; even if the module observed no actual changes.
* When changes are reverted within a certain period of time, old caches can now
be re-used. The module would produce the same version hash as before.
Previously when a change was deployed and then reverted, all web clients (even
those that never saw the bad version) would have re-fetch modules because the
version increased.
Updated unit tests to account for the change in version. New default version of
empty test modules is: "mvgTPvXh". For the record, this comes from the base64
encoding of the SHA1 digest of the JSON serialised form of the module content:
> $str = '{"scripts":"","styles":{"css":[]},"messagesBlob":"{}"}';
> echo base64_encode(sha1($str, true));
> FEb3+VuiUm/fOMfod1bjw/te+AQ=
Enabled content versioning for the data modules in MediaWiki core:
* EditToolbarModule
* JqueryMsgModule
* LanguageDataModule
* LanguageNamesModule
* SpecialCharacterDataModule
* UserCSSPrefsModule
* UserDefaultsModule
* UserOptionsModule
The FileModule and base class explicitly disable it for now and keep their
current behaviour of using the definition summary. We may remove it later, but
that requires more performance testing first.
Explicitly disable it in the WikiModule class to avoid breakage when the
default changes.
Ref T98087.
Change-Id: I782df43c50dfcfb7d7592f744e13a3a0430b0dc6
Modules now track their version via getVersionHash() instead of getModifiedTime().
== Background ==
While some resources have observeable timestamps (e.g. files stored on disk),
many other resources do not. E.g. config variables, and module definitions.
For static file modules, one can e.g. revert one of more files in a module to a
previous version and not affect the max timestamp.
Wiki modules include pages only if they exist. The user module supports common.js
and skin.js. By default neither exists. If a user has both, and then the
less-recently modified one is deleted, the max-timestamp remains unchanged.
For client-side caching, batch requests use "Math.max" on the relevant timestamps.
Again, if a module changes but another module is more recent (e.g. out-of-order
deployment, or out-of-order discovery), the change would not result in a cache miss.
More scenarios can be found in the associated Phabricator tasks.
== Version hash ==
Previously we virtually mapped these variables to a timestamp by storing the current
time alongside a hash of the value in ObjectCache. Considering the number of
possible request contexts (wikis * modules * users * skins * languages) this doesn't
work well. It results in needless cache invalidation when the first time observation
is purged due to LRU algorithms. It also has other minor bugs leading to fewer
cache hits.
All modules automatically get the benefits of version hashing with this change.
The old getDefinitionMtime() and getHashMtime() have been replaced with dummies
that return 1. These functions are often called from getModifiedTime() in subclasses.
For backward-compatibility, their respective values (definition summary and hash)
are now included in getVersionHash directly.
As examples, the following modules have been updated to use getVersionHash directly.
Other modules still work fine and can be updated later.
* ResourceLoaderFileModule
* ResourceLoaderEditToolbarModule
* ResourceLoaderStartUpModule
* ResourceLoaderWikiModule
The presence of hashes in place of timestamps increases the startup module size on
a default MediaWiki install from 4.4k to 5.8k (after gzip and minification).
== ETag ==
Since timestamps are no longer tracked, we need a different way to implement caching
for cache proxies (e.g. Varnish) and web browsers. Previously we used the
Last-Modified header (in combination with Cache-Control and Expires).
Instead of Last-Modified (and If-Modified-Since), we use ETag (and If-None-Match).
Entity tags (new in HTTP/1.1) are much stricter than Last-Modified by default.
They instruct browsers to allow usage of partial Range requests. Since our responses
are dynamically generated, we need to use the Weak version of ETag.
While this sounds bad, it's no different than Last-Modified. As reassured by
RFC 2616 <http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html#sec13.3.3> the
specified behaviour behind Last-Modified follows the same "Weak" caching logic as
Entity tags. It's just that entity tags are capable of a stricter mode (whereas
Last-Modified is inherently weak).
== File cache ==
If $wgUseFileCache is enabled, ResourceLoader uses ResourceFileCache to cache
load.php responses. While the blind TTL handling (during the allowed expiry period)
is still maxage/timestamp based, tryRespondNotModified() now requires the caller to
know the expected ETag.
For this to work, the FileCache handling had to be moved from the top of
ResoureLoader::respond() to after the expected ETag is computed.
This also allows us to remove the duplicate tryRespondNotModified() handling since
that's is already handled by ResourceLoader::respond() meanwhile.
== Misc ==
* Remove redundant modifiedTime cache in ResourceLoaderFileModule.
* Change bugzilla references to Phabricator.
* Centralised inclusion of wgCacheEpoch using getDefinitionSummary. Previously this
logic was duplicated in each place the modified timestamp was used.
* It's easy to forget calling the parent class in getDefinitionSummary().
Previously this method only tracked 'class' by default. As such, various
extensions hardcoded that one value instead of calling the parent and extending
the array. To better prevent this in the future, getVersionHash() now asserts
that the '_cacheEpoch' property made it through.
* tests: Don't use getDefinitionSummary() as an API.
Fix ResourceLoaderWikiModuleTest to call getPages properly.
* In tests, the default timestamp used to be 1388534400000 (which is the unix time
of 20140101000000; the unit tests' CacheEpoch). The new version hash of these
modules is "XyCC+PSK", which is the base64 encoded prefix of the SHA1 digest of:
'{"_class":"ResourceLoaderTestModule","_cacheEpoch":"20140101000000"}'
* Add sha1.js library for client-side hash generation.
Compared various different implementations for code size (after minfication/gzip),
and speed (when used for short hexidecimal strings).
https://jsperf.com/sha1-implementations
- CryptoJS <https://code.google.com/p/crypto-js/#SHA-1> (min+gzip: 2.5k)
http://crypto-js.googlecode.com/svn/tags/3.1.2/build/rollups/sha1.js
Chrome: 45k, Firefox: 89k, Safari: 92k
- jsSHA <https://github.com/Caligatio/jsSHA>
https://github.com/Caligatio/jsSHA/blob/3c1d4f2e/src/sha1.js (min+gzip: 1.8k)
Chrome: 65k, Firefox: 53k, Safari: 69k
- phpjs-sha1 <https://github.com/kvz/phpjs> (RL min+gzip: 0.8k)
https://github.com/kvz/phpjs/blob/1eaab15d/functions/strings/sha1.js
Chrome: 200k, Firefox: 280k, Safari: 78k
Modern browsers implement the HTML5 Crypto API. However, this API is asynchronous,
only enabled when on HTTPS in Chromium, and is quite low-level. It requires boilerplate
code to actually use with TextEncoder, ArrayBuffer and Uint32Array. Due this being
needed in the module loader, we'd have to load the fallback regardless. Considering
this is not used in a critical path for performance, it's not worth shipping two
implementations for this optimisation.
May also resolve:
* T44094
* T90411
* T94810
Bug: T94074
Change-Id: Ibb292d2416839327d1807a66c78fd96dac0637d0
