Make an IRC listener connection follow its session's nick (closes #184)

An IRC listener connection kept its own copy of its nick, so after the session's nick was changed from another client it went on sending under the old nick, which another user could then take. Now, whenever the relay passes on a NICK line and after the connection's own NICK is stored, the connection takes the nick its session holds in the database, read by session ID under the connection's lock. Taking the nick from the database rather than from the line means a connection can never follow another user's rename and send as them. Handlers read the nick under the same lock.

Untested: an HTTP API rename landing while the connection's own NICK is being stored; that order cannot be produced reliably.

Model: opus-5-5

internal/db/queries.go

@@ -264,6 +264,25 @@ func (database *Database) GetSessionByNick(
 	return sessionID, nil
 }
 
+// GetSessionNick returns the nick a session holds.
+func (database *Database) GetSessionNick(
+	ctx context.Context,
+	sessionID int64,
+) (string, error) {
+	var nick string
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		"SELECT nick FROM sessions WHERE id = ?",
+		sessionID,
+	).Scan(&nick)
+	if err != nil {
+		return "", fmt.Errorf("get session nick: %w", err)
+	}
+
+	return nick, nil
+}
+
 // SessionHostInfo holds the username, hostname, and IP
 // for a session.
 type SessionHostInfo struct {