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, 35 insertions, 0 deletions

diff --git a/src/or/connection_edge.c b/src/or/connection_edge.c
index ce555ed5e2..20f01b15f6 100644
--- a/src/or/connection_edge.c
+++ b/src/or/connection_edge.c
@@ -3414,3 +3414,38 @@ connection_edge_update_circuit_isolation(const edge_connection_t *conn,
   }
 }
 
+/**
+ * Clear the isolation settings on <b>circ</b>.
+ *
+ * This only works on an open circuit that has never had a stream attached to
+ * it, and whose isolation settings are hypothetical.  (We set hypothetical
+ * isolation settings on circuits as we're launching them, so that we
+ * know whether they can handle more streams or whether we need to launch
+ * even more circuits.  We clear the flags once the circuits are open,
+ * in case the streams that made us launch the circuits have closed
+ * since we began launching the circuits.)
+ */
+void
+circuit_clear_isolation(origin_circuit_t *circ)
+{
+  if (circ->isolation_any_streams_attached) {
+    log_warn(LD_BUG, "Tried to clear the isolation status of a dirty circuit");
+    return;
+  }
+  if (TO_CIRCUIT(circ)->state != CIRCUIT_STATE_OPEN) {
+    log_warn(LD_BUG, "Tried to clear the isolation status of a non-open "
+             "circuit");
+    return;
+  }
+
+  circ->isolation_values_set = 0;
+  circ->isolation_flags_mixed = 0;
+  circ->client_proto_type = 0;
+  circ->client_proto_socksver = 0;
+  circ->dest_port = 0;
+  tor_addr_make_unspec(&circ->client_addr);
+  tor_free(circ->dest_address);
+  circ->session_group = -1;
+  circ->nym_epoch = 0;
+}
+