PLT-2674 Private Group should not have Leave option when only one member remains (#2888)

api/channel.go

@@ -576,6 +576,7 @@ func leave(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	sc := Srv.Store.Channel().Get(id)
 	uc := Srv.Store.User().Get(c.Session.UserId)
+	ccm := Srv.Store.Channel().GetMemberCount(id)
 
 	if cresult := <-sc; cresult.Err != nil {
 		c.Err = cresult.Err
@@ -583,9 +584,13 @@ func leave(c *Context, w http.ResponseWriter, r *http.Request) {
 	} else if uresult := <-uc; uresult.Err != nil {
 		c.Err = cresult.Err
 		return
+	} else if ccmresult := <-ccm; ccmresult.Err != nil {
+		c.Err = ccmresult.Err
+		return
 	} else {
 		channel := cresult.Data.(*model.Channel)
 		user := uresult.Data.(*model.User)
+		membersCount := ccmresult.Data.(int64)
 
 		if !c.HasPermissionsToTeam(channel.TeamId, "leave") {
 			return
@@ -597,6 +602,12 @@ func leave(c *Context, w http.ResponseWriter, r *http.Request) {
 			return
 		}
 
+		if channel.Type == model.CHANNEL_PRIVATE && membersCount == 1 {
+			c.Err = model.NewLocAppError("leave", "api.channel.leave.last_member.app_error", nil, "userId="+user.Id)
+			c.Err.StatusCode = http.StatusBadRequest
+			return
+		}
+
 		if channel.Name == model.DEFAULT_CHANNEL {
 			c.Err = model.NewLocAppError("leave", "api.channel.leave.default.app_error", map[string]interface{}{"Channel": model.DEFAULT_CHANNEL}, "")
 			c.Err.StatusCode = http.StatusBadRequest

api/channel_test.go

@@ -485,8 +485,10 @@ func TestLeaveChannel(t *testing.T) {
 
 	Client.Must(Client.JoinChannel(channel1.Id))
 
-	// No error if you leave a channel you cannot see
-	Client.Must(Client.LeaveChannel(channel3.Id))
+	// Cannot leave a the private group if you are the only member
+	if _, err := Client.LeaveChannel(channel3.Id); err == nil {
+		t.Fatal("should have errored, cannot leave private group if only one member")
+	}
 
 	rchannel := Client.Must(Client.CreateDirectChannel(th.BasicUser.Id)).Data.(*model.Channel)