[tor-commits] [stem/master] Better type checking for RELAY cell replies

[atagar at torproject.org]

commit d60ac492e2f2abb4f2c0764e28d77eb096365b17
Author: Damian Johnson <atagar at torproject.org>
Date:   Sun Dec 30 14:58:55 2018 -0800

    Better type checking for RELAY cell replies
    
    The message we give when RELAY cells receive an unexpected response are pretty
    bad...
    
      ProtocolError: Circuit response should be a series of RELAY cells, but
      received an unexpected size for a response: 4048
    
    Instead checking the cell types, providing a more descriptive error if they
    mismatch. This doesn't fix the issue I'm trying to solve, but it gets me a bit
    closer to the true problem of ticket #28961...
    
      ProtocolError: RELAY cells should be 512 bytes, but received 464
---
 stem/client/__init__.py | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/stem/client/__init__.py b/stem/client/__init__.py
index 8e8bb118..c0d060ba 100644
--- a/stem/client/__init__.py
+++ b/stem/client/__init__.py
@@ -258,10 +258,12 @@ class Circuit(object):
       reply = self.relay._orport.recv()
       reply_cells = []
 
-      if len(reply) % self.relay.link_protocol.fixed_cell_length != 0:
-        raise stem.ProtocolError('Circuit response should be a series of RELAY cells, but received an unexpected size for a response: %i' % len(reply))
-
       while reply:
+        reply_cmd = stem.client.datatype.Size.CHAR.pop(reply[self.relay.link_protocol.circ_id_size.size:])[0]
+
+        if reply_cmd != stem.client.cell.RelayCell.VALUE:
+          raise stem.ProtocolError('Circuit response should be a series of RELAY cells, but received an unexpected %s (%i)' % (stem.client.cell.Cell.by_value(reply_cmd), reply_cmd))
+
         encrypted_cell, reply = split(reply, self.relay.link_protocol.fixed_cell_length)
         decrypted_cell, backward_key, backward_digest = stem.client.cell.RelayCell.decrypt(self.relay.link_protocol, encrypted_cell, self.backward_key, self.backward_digest)