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

plugin/rpcplugin/supervisor_test.go

@@ -0,0 +1,130 @@
+package rpcplugin
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/mattermost/platform/plugin"
+)
+
+func TestSupervisor(t *testing.T) {
+	dir, err := ioutil.TempDir("", "")
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	backend := filepath.Join(dir, "backend")
+	compileGo(t, `
+		package main
+
+		import (
+			"github.com/mattermost/platform/plugin"
+			"github.com/mattermost/platform/plugin/rpcplugin"
+		)
+
+		type MyPlugin struct {}
+
+		func (p *MyPlugin) OnActivate(api plugin.API) error {
+			return nil
+		}
+
+		func (p *MyPlugin) OnDeactivate() error {
+			return nil
+		}
+
+		func main() {
+			rpcplugin.Main(&MyPlugin{})
+		}
+	`, backend)
+
+	ioutil.WriteFile(filepath.Join(dir, "plugin.json"), []byte(`{"id": "foo", "backend": {"executable": "backend"}}`), 0600)
+
+	bundle := plugin.BundleInfoForPath(dir)
+	supervisor, err := SupervisorProvider(bundle)
+	require.NoError(t, err)
+	require.NoError(t, supervisor.Start())
+	require.NoError(t, supervisor.Hooks().OnActivate(nil))
+	require.NoError(t, supervisor.Stop())
+}
+
+// If plugin development goes really wrong, let's make sure plugin activation won't block forever.
+func TestSupervisor_StartTimeout(t *testing.T) {
+	dir, err := ioutil.TempDir("", "")
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	backend := filepath.Join(dir, "backend")
+	compileGo(t, `
+		package main
+
+		func main() {
+			for {
+			}
+		}
+	`, backend)
+
+	ioutil.WriteFile(filepath.Join(dir, "plugin.json"), []byte(`{"id": "foo", "backend": {"executable": "backend"}}`), 0600)
+
+	bundle := plugin.BundleInfoForPath(dir)
+	supervisor, err := SupervisorProvider(bundle)
+	require.NoError(t, err)
+	require.Error(t, supervisor.Start())
+}
+
+// Crashed plugins should be relaunched.
+func TestSupervisor_PluginCrash(t *testing.T) {
+	dir, err := ioutil.TempDir("", "")
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	backend := filepath.Join(dir, "backend")
+	compileGo(t, `
+		package main
+
+		import (
+			"os"
+
+			"github.com/mattermost/platform/plugin"
+			"github.com/mattermost/platform/plugin/rpcplugin"
+		)
+
+		type MyPlugin struct {}
+
+		func (p *MyPlugin) OnActivate(api plugin.API) error {
+			os.Exit(1)
+			return nil
+		}
+
+		func (p *MyPlugin) OnDeactivate() error {
+			return nil
+		}
+
+		func main() {
+			rpcplugin.Main(&MyPlugin{})
+		}
+	`, backend)
+
+	ioutil.WriteFile(filepath.Join(dir, "plugin.json"), []byte(`{"id": "foo", "backend": {"executable": "backend"}}`), 0600)
+
+	bundle := plugin.BundleInfoForPath(dir)
+	supervisor, err := SupervisorProvider(bundle)
+	require.NoError(t, err)
+	require.NoError(t, supervisor.Start())
+	require.Error(t, supervisor.Hooks().OnActivate(nil))
+
+	recovered := false
+	for i := 0; i < 30; i++ {
+		if supervisor.Hooks().OnDeactivate() == nil {
+			recovered = true
+			break
+		}
+		time.Sleep(time.Millisecond * 100)
+	}
+	assert.True(t, recovered)
+	require.NoError(t, supervisor.Stop())
+}