* 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.
* 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
* allow `Wait()`ing on the supervisor
In the event the plugin supervisor shuts down a plugin for crashing too
many times, the new `Wait()` interface allows the `ActivatePlugin` to
accept a callback function to trigger when `supervisor.Wait()` returns.
If the supervisor shuts down normally, this callback is invoked with
a nil error, otherwise any error reported by the supervisor is passed
along.
* improve plugin activation/deactivation logic
Avoid triggering activation of previously failed-to-start plugins just
becase something in the configuration changed. Now, intelligently
compare the global enable bit as well as the each individual plugin's
enabled bit.
* expose store to manipulate PluginStatuses
* expose API to fetch plugin statuses
* keep track of whether or not plugin sandboxing is supported
* transition plugin statuses
* restore error on plugin activation if already active
* don't initialize test plugins until successfully loaded
* emit websocket events when plugin statuses change
* skip pruning if already initialized
* MM-8622: maintain plugin statuses in memory
Switch away from persisting plugin statuses to the database, and
maintain in memory instead. This will be followed by a cluster interface
to query the in-memory status of plugin statuses from all cluster nodes.
At the same time, rename `cluster_discovery_id` on the `PluginStatus`
model object to `cluster_id`.
* MM-8622: aggregate plugin statuses across cluster
* fetch cluster plugin statuses when emitting websocket notification
* address unit test fixes after rebasing
* relax (poor) racey unit test re: supervisor.Wait()
* make store-mocks
* begin backend plugin wip
* flesh out rpcplugin. everything done except for minor supervisor stubs
* done with basic plugin infrastructure
* simplify tests
* remove unused test lines
