Plugin API hook for Shared Channel file attachment sync (#25874)

* option for auto inviting plugin to all shared channels.

* auto-invite remotes to shared channels when flag set

* fix unit test

* immediately ping new remotes; fix unique siteurl bug

* make i18n-extract

* fix translations

* plugin hooks for file attachments

* hook for profile image sync

* fix profile image sync

* fix unit test

---------

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

server/platform/services/sharedchannel/attachment.go

@@ -41,6 +41,10 @@ func (scs *Service) sendAttachmentForRemote(fi *model.FileInfo, post *model.Post
 		return fmt.Errorf("cannot update remote cluster for remote id %s; Remote Cluster Service not enabled", rc.RemoteId)
 	}
 
+	if rc.IsPlugin() {
+		return scs.sendAttachmentToPlugin(fi, post, rc)
+	}
+
 	us := &model.UploadSession{
 		Id:        model.NewId(),
 		Type:      model.UploadTypeAttachment,
@@ -120,11 +124,7 @@ func (scs *Service) sendAttachmentForRemote(fi *model.FileInfo, post *model.Post
 		}
 
 		// save file attachment record in SharedChannelAttachments table
-		sca := &model.SharedChannelAttachment{
-			FileId:   fi.Id,
-			RemoteId: rc.RemoteId,
-		}
-		if _, err2 := scs.server.GetStore().SharedChannel().UpsertAttachment(sca); err2 != nil {
+		if err2 := scs.saveSharedAttachment(&fi, rc); err2 != nil {
 			scs.server.Log().Log(mlog.LvlSharedChannelServiceError, "error saving SharedChannelAttachment",
 				mlog.String("remote", rc.DisplayName),
 				mlog.String("uploadId", usResp.Id),
@@ -140,6 +140,24 @@ func (scs *Service) sendAttachmentForRemote(fi *model.FileInfo, post *model.Post
 	})
 }
 
+// sendAttachmentToPlugin asynchronously sends a file attachment to a remote cluster.
+func (scs *Service) sendAttachmentToPlugin(fi *model.FileInfo, post *model.Post, rc *model.RemoteCluster) error {
+	if err := scs.app.OnSharedChannelsAttachmentSyncMsg(fi, post, rc); err != nil {
+		return fmt.Errorf("cannot send attachment to plugin %s: %w", rc.PluginID, err)
+	}
+	return scs.saveSharedAttachment(fi, rc)
+}
+
+// saveSharedAttachment saves the attachment in SharedChannelAttachments table.
+func (scs *Service) saveSharedAttachment(fi *model.FileInfo, rc *model.RemoteCluster) error {
+	sca := &model.SharedChannelAttachment{
+		FileId:   fi.Id,
+		RemoteId: rc.RemoteId,
+	}
+	_, err := scs.server.GetStore().SharedChannel().UpsertAttachment(sca)
+	return err
+}
+
 // onReceiveUploadCreate is called when a message requesting to create an upload session is received.  An upload session is
 // created and the id returned in the response.
 func (scs *Service) onReceiveUploadCreate(msg model.RemoteClusterMsg, rc *model.RemoteCluster, response *remotecluster.Response) error {