@dgrammatiko please hint me how this error handling posisble for online storage solution

You need to ask @laoneo for this, I'm not well educated on this

We should not have duplicate folder name validation on the server and client side. So all the client should do is to handle the error properly which comes from the server.

@laoneo but at current stage backend show msg error occured for all validation failure

cases that can handle by this pr

1. If user already have a folder name let's say ds if user try to make folder name d@s you get folder created success msg but actually you folder not created because php side validation remove @ in folder name and now folder name ds already exist so no folder created thus resticting user to enter only alphanumaric ,undersocore ,hyphen and period which accepted by php side.
2. when user give same file name which already exist only error occured but with this pr user get notification like folder already exist .
3. relative path error
   thus user not have to put it's effort to find error

Then you need to fix the server side to return proper errors.

Then you need to fix the server side to return proper errors.

yes that can also done but this will increase number of clicks by user .Best way that I got it to show error in modal by @dgrammatiko and from issue #39263 .

This pull request has been automatically rebased to 4.4-dev.

This pull request has been automatically rebased to 5.2-dev.