Shared channels plugin APIs for MS Teams plugin (#25805)

New plugin APIs and hooks for accessing Shared Channels service via plugin. 

- RegisterPluginForSharedChannels(opts model.RegisterPluginOpts) (remoteID string, err error)
- UnregisterPluginForSharedChannels(pluginID string) error
- ShareChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
- UpdateSharedChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
- UnshareChannel(channelID string) (unshared bool, err error)
- UpdateSharedChannelCursor(channelID, remoteID string, cusror model.GetPostsSinceForSyncCursor) error
- SyncSharedChannel(channelID string) error
- InviteRemoteToChannel(channelID string, remoteID string, userID string) error
- UninviteRemoteFromChannel(channelID string, remoteID string) error

Hooks
- OnSharedChannelsSyncMsg(msg *model.SyncMsg, rc *model.RemoteCluster) (model.SyncResponse, error)
- OnSharedChannelsPing(rc *model.RemoteCluster) bool

server/platform/services/remotecluster/ping.go

@@ -5,6 +5,7 @@ package remotecluster
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"time"
 
@@ -28,6 +29,7 @@ func (rcs *Service) pingGenerator(pingChan chan *model.RemoteCluster, done <-cha
 	defer close(pingChan)
 
 	for {
+		pingFreq := rcs.GetPingFreq()
 		start := time.Now()
 
 		// get all remotes, including any previously offline.
@@ -35,7 +37,7 @@ func (rcs *Service) pingGenerator(pingChan chan *model.RemoteCluster, done <-cha
 		if err != nil {
 			rcs.server.Log().Log(mlog.LvlRemoteClusterServiceError, "Ping remote cluster failed (could not get list of remotes)", mlog.Err(err))
 			select {
-			case <-time.After(PingFreq):
+			case <-time.After(pingFreq):
 				continue
 			case <-done:
 				return
@@ -50,8 +52,8 @@ func (rcs *Service) pingGenerator(pingChan chan *model.RemoteCluster, done <-cha
 
 		// try to maintain frequency
 		elapsed := time.Since(start)
-		if elapsed < PingFreq {
-			sleep := time.Until(start.Add(PingFreq))
+		if elapsed < pingFreq {
+			sleep := time.Until(start.Add(pingFreq))
 			select {
 			case <-time.After(sleep):
 			case <-done:
@@ -77,6 +79,7 @@ func (rcs *Service) pingEmitter(pingChan <-chan *model.RemoteCluster, done <-cha
 				rcs.server.Log().Log(mlog.LvlRemoteClusterServiceWarn, "Remote cluster ping failed",
 					mlog.String("remote", rc.DisplayName),
 					mlog.String("remoteId", rc.RemoteId),
+					mlog.String("pluginId", rc.PluginID),
 					mlog.Err(err),
 				)
 			}
@@ -93,25 +96,36 @@ func (rcs *Service) pingEmitter(pingChan <-chan *model.RemoteCluster, done <-cha
 	}
 }
 
+var ErrPluginPingFail = errors.New("plugin ping failed")
+
 // pingRemote make a synchronous ping to a remote cluster. Return is error if ping is
 // unsuccessful and nil on success.
 func (rcs *Service) pingRemote(rc *model.RemoteCluster) error {
-	frame, err := makePingFrame(rc)
-	if err != nil {
-		return err
-	}
-	url := fmt.Sprintf("%s/%s", rc.SiteURL, PingURL)
-
-	resp, err := rcs.sendFrameToRemote(PingTimeout, rc, frame, url)
-	if err != nil {
-		return err
-	}
-	rc.LastPingAt = model.GetMillis()
-
 	ping := model.RemoteClusterPing{}
-	err = json.Unmarshal(resp, &ping)
-	if err != nil {
-		return err
+
+	if rc.PluginID != "" {
+		ping.SentAt = model.GetMillis()
+		if ok := rcs.app.OnSharedChannelsPing(rc); !ok {
+			return ErrPluginPingFail
+		}
+		ping.RecvAt = model.GetMillis()
+	} else {
+		frame, err := makePingFrame(rc)
+		if err != nil {
+			return err
+		}
+		url := fmt.Sprintf("%s/%s", rc.SiteURL, PingURL)
+
+		resp, err := rcs.sendFrameToRemote(PingTimeout, rc, frame, url)
+		if err != nil {
+			return err
+		}
+		rc.LastPingAt = model.GetMillis()
+
+		err = json.Unmarshal(resp, &ping)
+		if err != nil {
+			return err
+		}
 	}
 
 	if err := rcs.server.GetStore().RemoteCluster().SetLastPingAt(rc.RemoteId); err != nil {
@@ -135,6 +149,7 @@ func (rcs *Service) pingRemote(rc *model.RemoteCluster) error {
 	rcs.server.Log().Log(mlog.LvlRemoteClusterServiceDebug, "Remote cluster ping",
 		mlog.String("remote", rc.DisplayName),
 		mlog.String("remoteId", rc.RemoteId),
+		mlog.String("pluginId", rc.PluginID),
 		mlog.Int("SentAt", ping.SentAt),
 		mlog.Int("RecvAt", ping.RecvAt),
 		mlog.Int("Diff", ping.RecvAt-ping.SentAt),