How to see if I connected to an ephemeral port?

Question

I'm working on a port scanner that uses Linux connect system call and when I'm scanning localhost, sometimes I get false positives due to kernel allocating me the source port for the connection that is equal to the destination port. Is there a way to tell if the connection I established was made to an ephemeral port?

Answer 1

You can use getsockname to find out the local port the kernel assigned. Alternatively, you could use bind to pick the port yourself.