A friendly anonymous user commented on legacy/trac#4115 that bridges can be distinguished by whether they use a create cell or create_fast cell. Once we fix legacy/trac#4115 it will be even more straightforward to distinguish. ``` should_use_create_fast_for_circuit(origin_circuit_t *circ) { or_options_t *options = get_options(); tor_assert(circ->cpath); tor_assert(circ->cpath->extend_info); if (!circ->cpath->extend_info->onion_key) return 1; /* our hand is forced: only a create_fast will work. */ if (!options->FastFirstHopPK) return 0; /* we prefer to avoid create_fast */ if (server_mode(options)) { /* We're a server, and we know an onion key. We can choose. * Prefer to blend in. */ return 0; } return 1; } ``` Bridge-detector example: ``` if (or_circ && !or_circ->is_first_hop && rh.command == RELAY_COMMAND_BEGIN_DIR) { /* non-mirror relay detected or bridge, filter it by consensus. */ ```