init: add -txsendrate configuration parameter

Adds a debug-only configuration option to set the target
transaction/second rate for relay to inbound connections. This is mostly
intended to be set to artificially low values to aid in testing behaviour
when a backlog occurs, but is also available in case the default 14tx/s
target is somehow too low in practice.

src/node/peerman_args.cpp

@@ -24,6 +24,10 @@ void ApplyArgsManOptions(const ArgsManager& argsman, PeerManager::Options& optio
 
     if (auto value{argsman.GetBoolArg("-blocksonly")}) options.ignore_incoming_txs = *value;
 
+    if (auto value{argsman.GetIntArg("-txsendrate")}) {
+        options.tx_send_rate = uint32_t(std::clamp<int64_t>(*value, 1, 1000));
+    }
+
     if (auto value{argsman.GetBoolArg("-privatebroadcast")}) options.private_broadcast = *value;
 }
 

src/node/txdownloadman.h

@@ -25,7 +25,7 @@ class TxDownloadManagerImpl;
 static constexpr int32_t MAX_PEER_TX_REQUEST_IN_FLIGHT = 100;
 /** Maximum number of transactions to consider for requesting, per peer. It provides a reasonable DoS limit to
  *  per-peer memory usage spent on announcements, while covering peers continuously sending INVs at the maximum
- *  rate (by our own policy, see INVENTORY_BROADCAST_PER_SECOND) for several minutes, while not receiving
+ *  rate (by our own policy, see DEFAULT_TX_SEND_RATE) for several minutes, while not receiving
  *  the actual transaction (from any peer) in response to requests for them. */
 static constexpr int32_t MAX_PEER_TX_ANNOUNCEMENTS = 5000;
 /** How long to delay requesting transactions via txids, if we have wtxid-relaying peers */