* plugins: compute bundle hash on load
Use this hash to bust client caches whenever the plugin bundle changes.
* eliminate redundant pluginHandler
* switch to 64-bit FNV-1a
* Fix test
* ensure plugin is always shutdown
Once we call `.client.Client()` the plugin has started, and must be shut
down. `newSupervisor` sometimes returned with an error (and without a
reference to the supervisor), leaving the client running indefinitely.
* Clarify the documentation to explain that plugin hooks will not trigger until `OnActivate` returns successfully, and will stop triggering just before `OnDeactivate` is called.
* test for plugin deadlock
* plugin/environment.go: switch to sync.Map
From: https://golang.org/pkg/sync/#Map
> If a goroutine holds a RWMutex for reading and another goroutine might call Lock, no goroutine should expect to be able to acquire a read lock until the initial read lock is released. In particular, this prohibits recursive read locking. This is to ensure that the lock eventually becomes available; a blocked Lock call excludes new readers from acquiring the lock.
The previous `RWMutex` was not safe given that we effectively acquired read locks recursively (hook -> api -> hook). This worked up until we activated or deactivated plugins, tried to acquire a write lock, and the plugin used the API to effectively trigger another hook.
Switching to sync.Map avoids this by divesting the need to lock at all, avoiding the potential for a recursive lock in the first place.
* Support `server`, deprecate `backend` in plugin manifest
This lets us converge on the use of the term `server` everywhere instead
of sometimes `backend` and sometimes `server`. We're still using
`webapp` and will eventually support `mobile` as well.
The plan is actually to rip out these deprecations as part of releasing
5.2, but I want to coordinate the extra additional breakage at the same
time, so for now this is a backwards compatible change.
* fix failing tests
* clean up plugins GoDoc:
- eliminate plugin.NewBlankContext() as unnecessary
- export ValidIdRegex as a string vs. the less readable var
- add/update various documentation strings
- hide everything by default, except where used by client plugins or the mattermost-server. The exception to this rule are the `*(Args|Returns)` structs which must be public for go-plugin, but are now prefixed with `Z_` with a warning not to use.
- include a top-level example to get plugin authors started
This is not a breaking change for existing plugins compiled against
plugins-v2.
* remove commented out ServeHTTPResponseWriter
* update examples to match developer docs
* add missing plugin/doc.go license header
