Fix round-robin for networks that support it

Some IRC networks perform round-robin by supplying a list of IP addresses
in their DNS records. However, Qt a) always uses the first address of that
list, and b) caches DNS records for a minute. This results that users who
connect at a roughly similar time (like at core startup) will all pick the
same IP for a given round-robin network address.

We now force Qt (simply by calling QHostInfo::fromName()) to perform a fresh
lookup every time it connects to an IRC network, which solves this problem.
However, this will not help you if your OS uses a system DNS cache that does
not reshuffle the list of IPs for repeated lookups.

diff --git a/src/core/corenetwork.cpp b/src/core/corenetwork.cpp
index 954565c..18f2784 100644 (file)
--- a/src/core/corenetwork.cpp
+++ b/src/core/corenetwork.cpp
@@ -18,6 +18,8 @@
  *   51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.         *
  ***************************************************************************/
 
+#include <QHostInfo>
+
 #include "corenetwork.h"
 
 #include "core.h"
@@ -184,6 +186,10 @@ void CoreNetwork::connectToIrc(bool reconnecting)
 
     enablePingTimeout();
 
+    // Qt caches DNS entries for a minute, resulting in round-robin (e.g. for chat.freenode.net) not working if several users
+    // connect at a similar time. QHostInfo::fromName(), however, always performs a fresh lookup, overwriting the cache entry.
+    QHostInfo::fromName(server.host);
+
 #ifdef HAVE_SSL
     if (server.useSsl) {
         CoreIdentity *identity = identityPtr();