Rework current_ip()

Use the same logic used in reprounzip-docker: connect to google.com,
then reads the local address on the socket.

vistrails/core/system/common.py

@@ -85,19 +85,43 @@ def current_user():
 def current_ip():
     """ current_ip() -> str
     Gets current IP address trying to avoid the IPv6 interface """
+    # Try to resolve the local hostname
     try:
-        info = socket.getaddrinfo(socket.gethostname(), None)
+        addresses = socket.getaddrinfo(socket.gethostname(), None)
+    except socket.gaierror:
+        pass
+    else:
         # Try to find an IPv4
-        for i in info:
+        for i in addresses:
             if i[0] == socket.AF_INET:
                 return i[4][0]
         # Return any address
-        for i in info:
+        for i in addresses:
             if i[0] in (socket.AF_INET, socket.AF_INET6):
                 return i[4][0]
-    except Exception, e:
-        debug.unexpected_exception(e)
-        return ''
+
+    # That didn't work, use whatever address lets you connect to google.com
+    try:
+        addresses = socket.getaddrinfo('google.com', 9, socket.AF_UNSPEC,
+                                       socket.SOCK_STREAM)
+    except socket.gaierror:
+        pass
+    else:
+        for address in addresses:
+            sock = None
+            try:
+                af, socktype, proto, canonname, sa = address
+                sock = socket.socket(af, socktype, proto)
+                sock.settimeout(1)
+                sock.connect(sa)
+                sock.close()
+            except socket.error:
+                pass
+            if sock is not None:
+                return sock.getsockname()[0]
+
+    # Couldn't find anything
+    return ''
 
 def current_time():
     """current_time() -> datetime.datetime