diff options
Diffstat (limited to 'src/or/relay.c')
| -rw-r--r-- | src/or/relay.c | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/src/or/relay.c b/src/or/relay.c index 5d06fd93fd..12283fcbbb 100644 --- a/src/or/relay.c +++ b/src/or/relay.c @@ -70,6 +70,9 @@ uint64_t stats_n_relay_cells_relayed = 0; */ uint64_t stats_n_relay_cells_delivered = 0; +/** Used to tell which stream to read from first on a circuit. */ +static tor_weak_rng_t stream_choice_rng = TOR_WEAK_RNG_INIT; + /** Update digest from the payload of cell. Assign integrity part to * cell. */ @@ -1740,6 +1743,12 @@ circuit_resume_edge_reading(circuit_t *circ, crypt_path_t *layer_hint) circ, layer_hint); } +void +stream_choice_seed_weak_rng(void) +{ + crypto_seed_weak_rng(&stream_choice_rng); +} + /** A helper function for circuit_resume_edge_reading() above. * The arguments are the same, except that <b>conn</b> is the head * of a linked list of edge streams that should each be considered. @@ -1755,11 +1764,18 @@ circuit_resume_edge_reading_helper(edge_connection_t *first_conn, int cells_on_queue; int cells_per_conn; edge_connection_t *chosen_stream = NULL; + int max_to_package; + + if (first_conn == NULL) { + /* Don't bother to try to do the rest of this if there are no connections + * to resume. */ + return 0; + } /* How many cells do we have space for? It will be the minimum of * the number needed to exhaust the package window, and the minimum * needed to fill the cell queue. */ - int max_to_package = circ->package_window; + max_to_package = circ->package_window; if (CIRCUIT_IS_ORIGIN(circ)) { cells_on_queue = circ->n_chan_cells.n; } else { @@ -1784,10 +1800,19 @@ circuit_resume_edge_reading_helper(edge_connection_t *first_conn, int num_streams = 0; for (conn = first_conn; conn; conn = conn->next_stream) { num_streams++; - if ((tor_weak_random() % num_streams)==0) + if (tor_weak_random_one_in_n(&stream_choice_rng, num_streams)) { chosen_stream = conn; + } /* Invariant: chosen_stream has been chosen uniformly at random from - * among the first num_streams streams on first_conn. */ + * among the first num_streams streams on first_conn. + * + * (Note that we iterate over every stream on the circuit, so that after + * we've considered the first stream, we've chosen it with P=1; and + * after we consider the second stream, we've switched to it with P=1/2 + * and stayed with the first stream with P=1/2; and after we've + * considered the third stream, we've switched to it with P=1/3 and + * remained with one of the first two streams with P=(2/3), giving each + * one P=(1/2)(2/3) )=(1/3).) */ } } |