Adds direct participants to the channel invite (#30404)

* Adds direct participants to the channel invite

The channel invite now contains the sanitized users that are local to
the node that is sending the invite. In the event that the receiving
server doesn't have those users in its local database, it can create
them from the invite and correctly generate the DM or GM with them as
members.

* Use IsRemote instead of directly checking user attributes

---------

Co-authored-by: Miguel de la Cruz <miguel@ctrlz.es>
Co-authored-by: Mattermost Build <build@mattermost.com>

server/platform/services/sharedchannel/channelinvite_test.go

@@ -23,6 +23,7 @@ import (
 
 var (
 	mockTypeChannel    = mock.AnythingOfType("*model.Channel")
+	mockTypeUser       = mock.AnythingOfType("*model.User")
 	mockTypeString     = mock.AnythingOfType("string")
 	mockTypeReqContext = mock.AnythingOfType("*request.Context")
 	mockTypeContext    = mock.MatchedBy(func(ctx context.Context) bool { return true })
@@ -264,18 +265,22 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 	t.Run("DM channels", func(t *testing.T) {
 		var testRemoteID = model.NewId()
 		testCases := []struct {
-			desc          string
-			user1         *model.User
-			user2         *model.User
-			canSee        bool
-			expectSuccess bool
+			desc                string
+			user1               *model.User
+			user2               *model.User
+			canSee              bool
+			expectSuccess       bool
+			user2InDB           bool
+			user2InParticipants bool
 		}{
-			{"valid users", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId()}, true, true},
-			{"swapped users", &model.User{Id: model.NewId()}, &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, true, true},
-			{"two remotes", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, true, false},
-			{"two locals", &model.User{Id: model.NewId()}, &model.User{Id: model.NewId()}, true, false},
-			{"can't see", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId()}, false, false},
-			{"invalid remoteid", &model.User{Id: model.NewId(), RemoteId: model.NewPointer("bogus")}, &model.User{Id: model.NewId()}, true, false},
+			{"valid users", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId()}, true, true, true, false},
+			{"swapped users", &model.User{Id: model.NewId()}, &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, true, true, true, false},
+			{"two remotes", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, true, false, true, false},
+			{"two locals", &model.User{Id: model.NewId()}, &model.User{Id: model.NewId()}, true, false, true, false},
+			{"can't see", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId()}, false, false, true, false},
+			{"invalid remoteid", &model.User{Id: model.NewId(), RemoteId: model.NewPointer("bogus")}, &model.User{Id: model.NewId()}, true, false, true, false},
+			{"user2 not in DB but in participants", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId()}, true, true, false, true},
+			{"user2 not in DB and not in participants", &model.User{Id: model.NewId(), RemoteId: &testRemoteID}, &model.User{Id: model.NewId()}, true, false, false, false},
 		}
 
 		for _, tc := range testCases {
@@ -298,6 +303,12 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 					Type:                 model.ChannelTypeDirect,
 					DirectParticipantIDs: []string{tc.user1.Id, tc.user2.Id},
 				}
+
+				// Add participants to the invitation if needed
+				if tc.user2InParticipants {
+					invitation.DirectParticipants = append(invitation.DirectParticipants, tc.user2)
+				}
+
 				payload, err := json.Marshal(invitation)
 				require.NoError(t, err)
 
@@ -313,8 +324,20 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 				mockUserStore := mocks.UserStore{}
 				mockUserStore.On("Get", mockTypeContext, tc.user1.Id).
 					Return(tc.user1, nil)
-				mockUserStore.On("Get", mockTypeContext, tc.user2.Id).
-					Return(tc.user2, nil)
+				if tc.user2InDB {
+					mockUserStore.On("Get", mockTypeContext, tc.user2.Id).
+						Return(tc.user2, nil)
+				} else {
+					mockUserStore.On("Get", mockTypeContext, tc.user2.Id).
+						Return(nil, &store.ErrNotFound{})
+				}
+
+				if tc.user2InParticipants {
+					mockUserStore.On("Save", mock.AnythingOfType("*request.Context"),
+						mock.MatchedBy(func(u *model.User) bool {
+							return u.Id == tc.user2.Id
+						})).Return(tc.user2, nil)
+				}
 
 				mockChannelStore.On("Get", invitation.ChannelId, true).Return(nil, errors.New("boom"))
 				mockChannelStore.On("GetByName", "", mockTypeString, true).Return(nil, &store.ErrNotFound{})
@@ -332,6 +355,7 @@ func TestOnReceiveChannelInvite(t *testing.T) {
 				mockApp.On("GetOrCreateDirectChannel", mockTypeReqContext, mockTypeString, mockTypeString, mock.AnythingOfType("model.ChannelOption")).
 					Return(channel, nil).Maybe()
 				mockApp.On("UserCanSeeOtherUser", mockTypeReqContext, mockTypeString, mockTypeString).Return(tc.canSee, nil).Maybe()
+				mockApp.On("NotifySharedChannelUserUpdate", mockTypeUser).Return().Maybe()
 
 				defer mockApp.AssertExpectations(t)