Check for possible dead-locks

[stv0g]

By @koraa in #27 (comment)

https://github.com/stv0g/go-rosenpass/blob/d7e38ecaf9e7803f2824a03ac24ac34944a53af6/server.go#L251

Severity: N/A – How do you make sure all these locks never cause a dead-lock situation?

[stv0g]

The go-rosenpass codebase:

• uses no channels which could potentially block
• uses two read-write mutexes (sync.RWMutex):
  • biscuitLock for safely rotating bisuit keys
  • handshakesLock for safely keeping a table of active (initiator-)handshakes

All locks are covering minimally sized critical regions (usually just an access to a slice or map) with no control flow paths allowing for keeping locks longer than necessary.