Return SessionAlreadyExists error in Occupant::add_session

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

src/error.rs

@@ -24,6 +24,7 @@ pub enum Error {
     MismatchJids(Jid, Jid),
     NickAlreadyAssigned(String),
     NonexistantSession(FullJid),
+    SessionAlreadyExists(FullJid),
     XMPPError(TokioXMPPError),
 }
 
@@ -35,6 +36,7 @@ impl fmt::Display for Error {
             Error::MismatchJids(jid1, jid2) => write!(f, "Mismatch Jids: {}, {}", jid1, jid2),
             Error::NickAlreadyAssigned(err) => write!(f, "Nickname already assigned: {}", err),
             Error::NonexistantSession(err) => write!(f, "Session doesn't exist: {}", err),
+            Error::SessionAlreadyExists(err) => write!(f, "Session already exist: {}", err),
             Error::XMPPError(err) => write!(f, "XMPP error: {}", err),
         }
     }

src/room.rs

@@ -224,6 +224,13 @@ impl Occupant {
             return Err(Error::MismatchJids(Jid::from(self.real.clone()), Jid::from(real.clone())));
         }
 
+        for session in &self.sessions {
+            if &real == session {
+                return Err(Error::SessionAlreadyExists(real))
+            }
+        }
+
+        self.sessions.push(real);
         Ok(())
     }