PLT-7407: Back-end plugin mechanism (#7177)

* 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

1 files changed, 123 insertions, 0 deletions

diff --git a/plugin/pluginenv/environment.go b/plugin/pluginenv/environment.go
new file mode 100644
index 000000000..36a8c6e76
--- /dev/null
+++ b/plugin/pluginenv/environment.go
@@ -0,0 +1,123 @@
+// Package pluginenv provides high level functionality for discovering and launching plugins.
+package pluginenv
+
+import (
+	"fmt"
+
+	"github.com/pkg/errors"
+
+	"github.com/mattermost/platform/plugin"
+)
+
+type APIProviderFunc func(*plugin.Manifest) (plugin.API, error)
+type SupervisorProviderFunc func(*plugin.BundleInfo) (plugin.Supervisor, error)
+
+// Environment represents an environment that plugins are discovered and launched in.
+type Environment struct {
+	searchPath         string
+	apiProvider        APIProviderFunc
+	supervisorProvider SupervisorProviderFunc
+	activePlugins      map[string]plugin.Supervisor
+}
+
+type Option func(*Environment)
+
+// Creates a new environment. At a minimum, the APIProvider and SearchPath options are required.
+func New(options ...Option) (*Environment, error) {
+	env := &Environment{
+		activePlugins: make(map[string]plugin.Supervisor),
+	}
+	for _, opt := range options {
+		opt(env)
+	}
+	if env.supervisorProvider == nil {
+		env.supervisorProvider = DefaultSupervisorProvider
+	}
+	if env.searchPath == "" {
+		return nil, fmt.Errorf("a search path must be provided")
+	} else if env.apiProvider == nil {
+		return nil, fmt.Errorf("an api provider must be provided")
+	}
+	return env, nil
+}
+
+// Returns a list of all plugins found within the environment.
+func (env *Environment) Plugins() ([]*plugin.BundleInfo, error) {
+	return ScanSearchPath(env.searchPath)
+}
+
+// Returns the ids of the currently active plugins.
+func (env *Environment) ActivePluginIds() (ids []string) {
+	for id := range env.activePlugins {
+		ids = append(ids, id)
+	}
+	return
+}
+
+// Activates the plugin with the given id.
+func (env *Environment) ActivatePlugin(id string) error {
+	if _, ok := env.activePlugins[id]; ok {
+		return fmt.Errorf("plugin already active: %v", id)
+	}
+	plugins, err := ScanSearchPath(env.searchPath)
+	if err != nil {
+		return err
+	}
+	var plugin *plugin.BundleInfo
+	for _, p := range plugins {
+		if p.Manifest != nil && p.Manifest.Id == id {
+			if plugin != nil {
+				return fmt.Errorf("multiple plugins found: %v", id)
+			}
+			plugin = p
+		}
+	}
+	if plugin == nil {
+		return fmt.Errorf("plugin not found: %v", id)
+	}
+	supervisor, err := env.supervisorProvider(plugin)
+	if err != nil {
+		return errors.Wrapf(err, "unable to create supervisor for plugin: %v", id)
+	}
+	api, err := env.apiProvider(plugin.Manifest)
+	if err != nil {
+		return errors.Wrapf(err, "unable to get api for plugin: %v", id)
+	}
+	if err := supervisor.Start(); err != nil {
+		return errors.Wrapf(err, "unable to start plugin: %v", id)
+	}
+	if err := supervisor.Hooks().OnActivate(api); err != nil {
+		supervisor.Stop()
+		return errors.Wrapf(err, "unable to activate plugin: %v", id)
+	}
+	env.activePlugins[id] = supervisor
+	return nil
+}
+
+// Deactivates the plugin with the given id.
+func (env *Environment) DeactivatePlugin(id string) error {
+	if supervisor, ok := env.activePlugins[id]; !ok {
+		return fmt.Errorf("plugin not active: %v", id)
+	} else {
+		delete(env.activePlugins, id)
+		err := supervisor.Hooks().OnDeactivate()
+		if serr := supervisor.Stop(); err == nil {
+			err = serr
+		}
+		return err
+	}
+}
+
+// Deactivates all plugins and gracefully shuts down the environment.
+func (env *Environment) Shutdown() (errs []error) {
+	for _, supervisor := range env.activePlugins {
+		if err := supervisor.Hooks().OnDeactivate(); err != nil {
+			errs = append(errs, err)
+		}
+		if err := supervisor.Stop(); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	env.activePlugins = make(map[string]plugin.Supervisor)
+	return
+}