X py: Adjust msg_id a bit so it behaves like stream_id in HTTP/2

- even for server initiated streams
- odd  for client initiated streams

This way I will be able to use Pkt.msg_id as real stream_id in go's Conn
because with even / odd scheme there is no possibility for id conflicts
in between two peers.

neo/lib/connection.py

@@ -340,7 +340,8 @@ class Connection(BaseConnection):
     def __init__(self, event_manager, *args, **kw):
         BaseConnection.__init__(self, event_manager, *args, **kw)
         self.read_buf = ReadBuffer()
-        self.cur_id = 0
+        # NOTE cur_id will be set in Server|Client to maintain `cur_id % 2 == const` invariant
+        #self.cur_id = 0
         self.aborted = False
         self.uuid = None
         self._queue = []
@@ -367,6 +368,7 @@ class Connection(BaseConnection):
         return self.server
 
     def asClient(self):
+        # TODO adjust .cur_id % 2 to be as client
         try:
             del self.idle
             assert self.client
@@ -374,6 +376,7 @@ class Connection(BaseConnection):
             self.client = True
 
     def asServer(self):
+        # TODO adjust .cur_id % 2 to be as server
         self.server = True
 
     def _closeClient(self):
@@ -406,7 +409,7 @@ class Connection(BaseConnection):
 
     def _getNextId(self):
         next_id = self.cur_id
-        self.cur_id = (next_id + 1) & 0xffffffff
+        self.cur_id = (next_id + 2) & 0xffffffff
         return next_id
 
     def updateTimeout(self, t=None):
@@ -599,6 +602,7 @@ class ClientConnection(Connection):
     """A connection from this node to a remote node."""
 
     client = True
+    cur_id = 1      # cur_id % 2 is 1 for client initiated "streams"
 
     def __init__(self, app, handler, node):
         self._ssl = app.ssl
@@ -660,6 +664,7 @@ class ServerConnection(Connection):
     KEEP_ALIVE = Connection.KEEP_ALIVE + 5
 
     server = True
+    cur_id = 0      # cur_id % 2 is 0 for server initated "streams"
 
     def __init__(self, *args, **kw):
         Connection.__init__(self, *args, **kw)

neo/tests/testConnection.py

@@ -77,14 +77,14 @@ class ConnectionTests(NeoUnitTestBase):
         use_case_list = (
             # (a) For a single packet sent at T,
             #     the limit time for the answer is T + (1 * CRITICAL_TIMEOUT)
-            ((), (1., 0)),
+            ((), (1., 1)),
             # (b) Same as (a), even if send another packet at (T + CT/2).
             #     But receiving a packet (at T + CT - ε) resets the timeout
             #     (which means the limit for the 2nd one is T + 2*CT)
-            ((.5, None), (1., 0, 2., 1)),
+            ((.5, None), (1., 1, 2., 3)),
             # (c) Same as (b) with a first answer at well before the limit
             #     (T' = T + CT/2). The limit for the second one is T' + CT.
-            ((.1, None, .5, 1), (1.5, 0)),
+            ((.1, None, .5, 3), (1.5, 1)),
         )
 
         def set_time(t):
@@ -106,7 +106,7 @@ class ConnectionTests(NeoUnitTestBase):
         try:
             for use_case, expected in use_case_list:
                 i = iter(use_case)
-                conn.cur_id = 0
+                conn.cur_id = 1     # XXX -> conn._reset() ?
                 set_time(0)
                 # No timeout when no pending request
                 self.assertEqual(conn._handlers.getNextTimeout(), None)