Let packetizer handle 0-length sends from channel.

If the channel is closed the send method returs a response length
of 0. This is not handled correctly by the packetizer and puts it
in an infinite loop. (Fixes #156 for real :-)

We make sure we don't do more than 10 iteration on a 0 length respose,
but raise an EOFError.

paramiko/packet.py

@@ -231,6 +231,7 @@ def read_all(self, n, check_rekey=False):
 
     def write_all(self, out):
         self.__keepalive_last = time.time()
+        iteration_with_zero_as_return_value = 0
         while len(out) > 0:
             retry_write = False
             try:
@@ -254,6 +255,15 @@ def write_all(self, out):
                 n = 0
                 if self.__closed:
                     n = -1
+            else:
+                if n == 0 and iteration_with_zero_as_return_value > 10:
+                # We shouldn't retry the write, but we didn't
+                # manage to send anything over the socket. This might be an
+                # indication that we have lost contact with the remote side,
+                # but are yet to receive an EOFError or other socket errors.
+                # Let's give it some iteration to try and catch up.
+                    n = -1
+                iteration_with_zero_as_return_value += 1
             if n < 0:
                 raise EOFError()
             if n == len(out):

tests/test_packetizer.py

@@ -74,3 +74,49 @@ def test_2_read(self):
         self.assertEqual(100, m.get_int())
         self.assertEqual(1, m.get_int())
         self.assertEqual(900, m.get_int())
+
+    def test_3_closed(self):
+        rsock = LoopSocket()
+        wsock = LoopSocket()
+        rsock.link(wsock)
+        p = Packetizer(wsock)
+        p.set_log(util.get_logger('paramiko.transport'))
+        p.set_hexdump(True)
+        cipher = AES.new(zero_byte * 16, AES.MODE_CBC, x55 * 16)
+        p.set_outbound_cipher(cipher, 16, sha1, 12, x1f * 20)
+
+        # message has to be at least 16 bytes long, so we'll have at least one
+        # block of data encrypted that contains zero random padding bytes
+        m = Message()
+        m.add_byte(byte_chr(100))
+        m.add_int(100)
+        m.add_int(1)
+        m.add_int(900)
+        wsock.send = lambda x: 0
+        from functools import wraps
+        import errno
+        import os
+        import signal
+
+        class TimeoutError(Exception):
+            pass
+
+        def timeout(seconds=1, error_message=os.strerror(errno.ETIME)):
+            def decorator(func):
+                def _handle_timeout(signum, frame):
+                    raise TimeoutError(error_message)
+
+                def wrapper(*args, **kwargs):
+                    signal.signal(signal.SIGALRM, _handle_timeout)
+                    signal.alarm(seconds)
+                    try:
+                        result = func(*args, **kwargs)
+                    finally:
+                        signal.alarm(0)
+                    return result
+
+                return wraps(func)(wrapper)
+
+            return decorator
+        send = timeout()(p.send_message)
+        self.assertRaises(EOFError, send, m)