Launch sufficient circuits to satisfy pending isolated streams

Our old "do we need to launch a circuit for stream S" logic was,
more or less, that if we had a pending circuit that could handle S,
we didn't need to launch a new one.

But now that we have streams isolated from one another, we need
something stronger here: It's possible that some pending C can
handle either S1 or S2, but not both.

This patch reuses the existing isolation logic for a simple
solution: when we decide during circuit launching that some pending
C would satisfy stream S1, we "hypothetically" mark C as though S1
had been connected to it.  Now if S2 is incompatible with S1, it
won't be something that can attach to C, and so we'll launch a new
stream.

When the circuit becomes OPEN for the first time (with no streams
attached to it), we reset the circuit's isolation status.  I'm not
too sure about this part: I wanted some way to be sure that, if all
streams that would have used a circuit die before the circuit is
done, the circuit can still get used.  But I worry that this
approach could also lead to us launching too many circuits.  Careful
thought needed here.

1 files changed, 16 insertions, 2 deletions

diff --git a/src/or/circuitlist.c b/src/or/circuitlist.c
index 9f688801f3..6f17697b21 100644
--- a/src/or/circuitlist.c
+++ b/src/or/circuitlist.c
@@ -210,9 +210,23 @@ circuit_set_state(circuit_t *circ, uint8_t state)
     /* add to waiting-circuit list. */
     smartlist_add(circuits_pending_or_conns, circ);
   }
-  if (state == CIRCUIT_STATE_OPEN)
-    tor_assert(!circ->n_conn_onionskin);
+
   circ->state = state;
+
+  if (state == CIRCUIT_STATE_OPEN) {
+    tor_assert(!circ->n_conn_onionskin);
+    if (CIRCUIT_IS_ORIGIN(circ)) {
+      origin_circuit_t *origin_circ = TO_ORIGIN_CIRCUIT(circ);
+      if (origin_circ->isolation_values_set &&
+          !origin_circ->isolation_any_streams_attached) {
+        /* If we have any isolation information set on this circuit,
+         * but we never attached any streams to it, then all of the
+         * isolation information was hypothetical.  Clear it.
+         */
+        circuit_clear_isolation(origin_circ);
+      }
+    }
+  }
 }
 
 /** Add <b>circ</b> to the global list of circuits. This is called only from