Use of SO_REUSEADDR

[vshu3000]

1908     // Make 'reuse address' option available
1909     int yes = 1;
1910     setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, reinterpret_cast<char *>(&yes),
1911                sizeof(yes));
1912 
1913 #ifdef SO_REUSEPORT
1914     setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, reinterpret_cast<char *>(&yes),
1915                sizeof(yes));
1916 #endif

So now it always reuses socket. The line outside ifdef should be removed.

[vshu3000]

The code actually always tries to reuse port. That means in my case two servers can bind to the same port without causing EADDRINUSE. This is unexpected behavior.

[yhirose]

@vshu3000, the main reason why I use SO_REUSEADDR is described in the first paragraph of this answer in stack overflow post

https://stackoverflow.com/questions/577885/what-are-the-use-cases-of-so-reuseaddr#answer-577905

It says "For TCP, the primary purpose is to restart a closed/killed process on the same address.". I still need this behavior, but I understand it may cause the security problem. I'll think about it to fulfill both requirements.

[yhirose]

We need to handle this matter carefully according to the following information:
https://stackoverflow.com/questions/14388706/how-do-so-reuseaddr-and-so-reuseport-differ

We cannot simply remove the use of SO_REUSEADDR. On Windows, using SO_REUSEADDR and SO_EXCLUSIVEADDRUSE would be a correct answer.

On operating systems supporting SO_REUSEPORT, we don't need to use SO_REUSEADDR. On other OSs which don't support SO_REUSEPORT however, we have to choose either the reusability of the address or the exclusive address use.