Duplicate EraseFDs Entries Can Cause Wrong Filedescriptor `close()` behaviour

[clauspruefer]

Current Implementation

In ClientHandler.cpp on client connection close or other error conditions other than EWOULDBLOCK, EAGAIN , currently a vector<ClientFD_t> EraseFDs; is used to save client filedescriptors for closing after data processing.

Problem

The vector type causes problems when multiple push_back(ClientFD) happen. The current processing in the erase loop only erases the first element if two same vector elements exist leaving the same filedescriptor inside the vector. On the next erase loop iteration, the filedescriptor with its ID could have been re-assigned for a new client and immediately gets closed where it should not.

Solution

Replace the std::vector with a std::set and replace push_back() with insert().