Enforce DNS resolution timeout

scrapy/resolver.py

@@ -16,8 +16,11 @@ class CachingThreadedResolver(ThreadedResolver):
     def getHostByName(self, name, timeout=None):
         if name in dnscache:
             return defer.succeed(dnscache[name])
-        if not timeout:
-            timeout = self.timeout
+        # in Twisted<=16.6, getHostByName() is always called with
+        # a default timeout of 60s (actually passed as (1, 3, 11, 45) tuple),
+        # so the input argument above is simply overridden
+        # to enforce Scrapy's DNS_TIMEOUT setting's value
+        timeout = (self.timeout,)
         d = super(CachingThreadedResolver, self).getHostByName(name, timeout)
         d.addCallback(self._cache_result, name)
         return d