MM-49984: Displaying active search backend in system console (#22721)

This will be shown in the system console to let users know
which search backend is active.

Implemented via adding an extra param in the ping response.

https://mattermost.atlassian.net/browse/MM-49984

```release-note
The database section in the system console now has an additional
read-only section which shows the active search backend in use.

This can be helpful to confirm which is the currently active
search engine when there are multiple of them configured.
```
---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/system.go

@@ -190,6 +190,8 @@ func getSystemPing(c *Context, w http.ResponseWriter, r *http.Request) {
 		s["CanReceiveNotifications"] = c.App.SendTestPushNotification(deviceID)
 	}
 
+	s["ActiveSearchBackend"] = c.App.ActiveSearchBackend()
+
 	if s[model.STATUS] != model.StatusOk {
 		w.WriteHeader(http.StatusInternalServerError)
 	}

server/channels/app/app_iface.go

@@ -400,6 +400,7 @@ type AppIface interface {
 	VerifyPlugin(plugin, signature io.ReadSeeker) *model.AppError
 	AccountMigration() einterfaces.AccountMigrationInterface
 	ActivateMfa(userID, token string) *model.AppError
+	ActiveSearchBackend() string
 	AddChannelsToRetentionPolicy(policyID string, channelIDs []string) *model.AppError
 	AddConfigListener(listener func(*model.Config, *model.Config)) string
 	AddDirectChannels(c request.CTX, teamID string, user *model.User) *model.AppError

server/channels/app/opentracing/opentracing_layer.go

@@ -89,6 +89,23 @@ func (a *OpenTracingAppLayer) ActivateMfa(userID string, token string) *model.Ap
 	return resultVar0
 }
 
+func (a *OpenTracingAppLayer) ActiveSearchBackend() string {
+	origCtx := a.ctx
+	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.ActiveSearchBackend")
+
+	a.ctx = newCtx
+	a.app.Srv().Store().SetContext(newCtx)
+	defer func() {
+		a.app.Srv().Store().SetContext(origCtx)
+		a.ctx = origCtx
+	}()
+
+	defer span.Finish()
+	resultVar0 := a.app.ActiveSearchBackend()
+
+	return resultVar0
+}
+
 func (a *OpenTracingAppLayer) AddChannelMember(c request.CTX, userID string, channel *model.Channel, opts app.ChannelMemberOpts) (*model.ChannelMember, *model.AppError) {
 	origCtx := a.ctx
 	span, newCtx := tracing.StartSpanWithParentByContext(a.ctx, "app.AddChannelMember")

server/channels/app/searchengine.go

@@ -60,3 +60,7 @@ func (a *App) PurgeBleveIndexes() *model.AppError {
 	}
 	return nil
 }
+
+func (a *App) ActiveSearchBackend() string {
+	return a.ch.srv.platform.SearchEngine.ActiveEngine()
+}

server/i18n/en.json

@@ -7795,6 +7795,10 @@
     "id": "ent.elasticsearch.indexer.index_batch.nothing_left_to_index.error",
     "translation": "Trying to index a new batch when all the entities are completed"
   },
+  {
+    "id": "ent.elasticsearch.max_version.app_error",
+    "translation": "Elasticsearch version {{.Version}} is higher than max supported version of {{.MaxVersion}}"
+  },
   {
     "id": "ent.elasticsearch.not_started.error",
     "translation": "Elasticsearch is not started"
@@ -7863,10 +7867,6 @@
     "id": "ent.elasticsearch.search_users.unmarshall_user_failed",
     "translation": "Failed to decode search results"
   },
-  {
-    "id": "ent.elasticsearch.start.already_started.app_error",
-    "translation": "Elasticsearch is already started."
-  },
   {
     "id": "ent.elasticsearch.start.create_bulk_processor_failed.app_error",
     "translation": "Failed to create Elasticsearch bulk processor."

server/platform/services/searchengine/searchengine.go

@@ -45,8 +45,19 @@ func (seb *Broker) GetActiveEngines() []SearchEngineInterface {
 	if seb.ElasticsearchEngine != nil && seb.ElasticsearchEngine.IsActive() {
 		engines = append(engines, seb.ElasticsearchEngine)
 	}
-	if seb.BleveEngine != nil && seb.BleveEngine.IsActive() {
+	if seb.BleveEngine != nil && seb.BleveEngine.IsActive() && seb.BleveEngine.IsIndexingEnabled() {
 		engines = append(engines, seb.BleveEngine)
 	}
 	return engines
 }
+
+func (seb *Broker) ActiveEngine() string {
+	activeEngines := seb.GetActiveEngines()
+	if len(activeEngines) > 0 {
+		return activeEngines[0].GetName()
+	}
+	if *seb.cfg.SqlSettings.DisableDatabaseSearch {
+		return "none"
+	}
+	return "database"
+}

server/platform/services/searchengine/searchengine_test.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package searchengine
+
+import (
+	"testing"
+
+	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/v6/server/platform/services/searchengine/mocks"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestActiveEngine(t *testing.T) {
+	cfg := &model.Config{}
+	cfg.SetDefaults()
+
+	b := NewBroker(cfg)
+
+	esMock := &mocks.SearchEngineInterface{}
+	esMock.On("IsActive").Return(true)
+	esMock.On("GetName").Return("elasticsearch")
+
+	bleveMock := &mocks.SearchEngineInterface{}
+	bleveMock.On("IsActive").Return(true)
+	bleveMock.On("IsIndexingEnabled").Return(true)
+	bleveMock.On("GetName").Return("bleve")
+
+	assert.Equal(t, "database", b.ActiveEngine())
+
+	b.ElasticsearchEngine = esMock
+	assert.Equal(t, "elasticsearch", b.ActiveEngine())
+
+	b.ElasticsearchEngine = nil
+	b.BleveEngine = bleveMock
+	assert.Equal(t, "bleve", b.ActiveEngine())
+
+	b.BleveEngine = nil
+	*b.cfg.SqlSettings.DisableDatabaseSearch = true
+
+	assert.Equal(t, "none", b.ActiveEngine())
+}