AsyncUDPSocket: abstract do_read function

This basically implements read handling, without catching all
exceptions. When using the socket in synchronous mode, it's useful to
avoid losing exception data (which, in an async daemon, can only be
logged)

Signed-off-by: Guido Trotter <ultrotter@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>

lib/daemon.py

@@ -91,20 +91,23 @@ class AsyncUDPSocket(asyncore.dispatcher):
     # differ and treat all messages equally.
     pass
 
+  def do_read(self):
+    try:
+      payload, address = self.recvfrom(constants.MAX_UDP_DATA_SIZE)
+    except socket.error, err:
+      if err.errno == errno.EINTR:
+        # we got a signal while trying to read. no need to do anything,
+        # handle_read will be called again if there is data on the socket.
+        return
+      else:
+        raise
+    ip, port = address
+    self.handle_datagram(payload, ip, port)
+
   # this method is overriding an asyncore.dispatcher method
   def handle_read(self):
     try:
-      try:
-        payload, address = self.recvfrom(constants.MAX_UDP_DATA_SIZE)
-      except socket.error, err:
-        if err.errno == errno.EINTR:
-          # we got a signal while trying to read. no need to do anything,
-          # handle_read will be called again if there is data on the socket.
-          return
-        else:
-          raise
-      ip, port = address
-      self.handle_datagram(payload, ip, port)
+      self.do_read()
     except: # pylint: disable-msg=W0702
       # we need to catch any exception here, log it, but proceed, because even
       # if we failed handling a single request, we still want to continue.