Always use the loopback interface when local

If the backend is local to the frontend then we will always use the
loopback interface instead of connecting on the external IP. This adds
some resilience to setups where the network connection may drop, e.g.
using wifi - especially Ubuntu which removes the IP from the interface
if it detects that the network is unreachable.

mythtv/libs/libmythbase/mythsocket.cpp

@@ -13,6 +13,8 @@
 // Qt
 #include <QByteArray>
 #include <QHostInfo>
+#include <QNetworkInterface> // for QNetworkInterface::allAddresses ()
+#include <QAbstractSocket> // for QAbstractSocket::NetworkLayerProtocol
 #include <QMap>
 #include <QCoreApplication>
 
@@ -37,6 +39,8 @@ const uint MythSocket::kLongTimeout  = kMythSocketLongTimeout;
 QMutex MythSocket::s_readyread_thread_lock;
 MythSocketThread *MythSocket::s_readyread_thread = NULL;
 
+QMap<QString, QHostAddress::SpecialAddress> MythSocket::s_loopback_cache;
+
 MythSocket::MythSocket(int socket, MythSocketCBs *cb)
     : MSocketDevice(MSocketDevice::Stream),            m_cb(cb),
       m_useReadyReadCallback(true),
@@ -752,6 +756,7 @@ void MythSocket::Unlock(bool wake_readyread) const
 bool MythSocket::connect(const QString &host, quint16 port)
 {
     QHostAddress hadr;
+
     if (!hadr.setAddress(host))
     {
         QHostInfo info = QHostInfo::fromName(host);
@@ -774,15 +779,45 @@ bool MythSocket::connect(const QString &host, quint16 port)
  *  \brief connect to host
  *  \return true on success
  */
-bool MythSocket::connect(const QHostAddress &addr, quint16 port)
+bool MythSocket::connect(const QHostAddress &hadr, quint16 port)
 {
+    QHostAddress addr = hadr;
+
     if (state() == Connected)
     {
         LOG(VB_SOCKET, LOG_ERR, LOC +
             "connect() called with already open socket, closing");
         close();
     }
 
+    bool usingLoopback = false;
+    if (s_loopback_cache.contains(addr.toString()))
+    {
+        addr = QHostAddress(s_loopback_cache.value(addr.toString()));
+        usingLoopback = true;
+    }
+    else
+    {
+        QList<QHostAddress> localIPs = QNetworkInterface::allAddresses();
+        for (int i = 0; i < localIPs.count() && !usingLoopback; ++i)
+        {
+            if (addr == localIPs[i])
+            {
+                QHostAddress::SpecialAddress loopback = QHostAddress::LocalHost;
+                if (addr.protocol() == QAbstractSocket::IPv6Protocol)
+                    loopback = QHostAddress::LocalHostIPv6;
+
+                s_loopback_cache[addr.toString()] = loopback;
+                addr = QHostAddress(loopback);
+                usingLoopback = true;
+            }
+        }
+    }
+
+    if (usingLoopback)
+        LOG(VB_SOCKET, LOG_INFO, LOC + QString("IP is local, using "
+                                               "loopback address instead"));
+
     LOG(VB_SOCKET, LOG_INFO, LOC + QString("attempting connect() to (%1:%2)")
             .arg(addr.toString()).arg(port));
 

mythtv/libs/libmythbase/mythsocket.h

@@ -9,6 +9,9 @@
 #include "mythsocket_cb.h"
 #include "mythbaseexp.h"
 
+template<class T >
+class QList;
+class QString;
 class QHostAddress;
 class MythSocketThread;
 
@@ -73,7 +76,7 @@ class MBASE_PUBLIC MythSocket : public MSocketDevice
     bool readData(char *data, quint64 len);
     bool writeData(const char *data, quint64 len);
 
-    bool connect(const QHostAddress &addr, quint16 port);
+    bool connect(const QHostAddress &hadr, quint16 port);
     bool connect(const QString &host, quint16 port);
 
     void Lock(void) const;
@@ -107,6 +110,8 @@ class MBASE_PUBLIC MythSocket : public MSocketDevice
     static const uint kSocketBufferSize;
     static QMutex s_readyread_thread_lock;
     static MythSocketThread *s_readyread_thread;
+
+    static QMap<QString, QHostAddress::SpecialAddress> s_loopback_cache;
 };
 
 #endif