Does Bitcoin Core really use random delay in transaction relay?

Question

I read that bitcoin uses random delay when relaying transaction to other peers in order to protect privacy. When I read the source code of the newest Bitcoin Core, I found a function called rand_uniform_delay. When I searched for its usage, I found it only used in random_test.cpp. I wonder where the code for the random delay in Bitcoin Core can be found.

Answer 1

Code used for better privacy when relaying transactions in \src\net_processing.cpp:

        if (auto tx_relay = peer->GetTxRelay(); tx_relay != nullptr) {
                LOCK(tx_relay->m_tx_inventory_mutex);
                // Check whether periodic sends should happen
                bool fSendTrickle = pto->HasPermission(NetPermissionFlags::NoBan);
                if (tx_relay->m_next_inv_send_time < current_time) {
                    fSendTrickle = true;
                    if (pto->IsInboundConn()) {
                        tx_relay->m_next_inv_send_time = NextInvToInbounds(current_time, INBOUND_INVENTORY_BROADCAST_INTERVAL);
                    } else {
                        tx_relay->m_next_inv_send_time = GetExponentialRand(current_time, OUTBOUND_INVENTORY_BROADCAST_INTERVAL);
                    }
                }

This was initially implemented by Pieter Wuille in #7125, later improved in #7840 and #13298

---

Related

Transaction Relay and trickling in Bitcoin