feat: event emitter will now emit new_txid in-case a tx replaces another

CHANGELOG.md

@@ -8,10 +8,12 @@ and this project adheres to the versioning scheme outlined in the [README.md](RE
 ## [Unreleased]
 
 ### Added
+
 - Add `tenure_timeout_secs` to the miner for determining when a time-based tenure extend should be attempted.
 
 ### Changed
 
+- When a transaction is dropped due to replace-by-fee, the `/drop_mempool_tx` event observer payload now includes `new_txid`, which is the transaction that replaced this dropped transaction. When a transaction is dropped for other reasons, `new_txid` is `null`. [#5381](https://github.com/stacks-network/stacks-core/pull/5381)
 - Nodes will assume that all PoX anchor blocks exist by default, and stall initial block download indefinitely to await their arrival (#5502)
 
 ## [3.1.0.0.1]

stackslib/src/chainstate/stacks/miner.rs

@@ -1427,8 +1427,16 @@ impl<'a> StacksMicroblockBuilder<'a> {
         self.runtime.num_mined = num_txs;
 
         mem_pool.drop_txs(&invalidated_txs)?;
-        event_dispatcher.mempool_txs_dropped(invalidated_txs, MemPoolDropReason::TOO_EXPENSIVE);
-        event_dispatcher.mempool_txs_dropped(to_drop_and_blacklist, MemPoolDropReason::PROBLEMATIC);
+        event_dispatcher.mempool_txs_dropped(
+            invalidated_txs,
+            None,
+            MemPoolDropReason::TOO_EXPENSIVE,
+        );
+        event_dispatcher.mempool_txs_dropped(
+            to_drop_and_blacklist,
+            None,
+            MemPoolDropReason::PROBLEMATIC,
+        );
 
         if blocked {
             debug!(
@@ -2543,8 +2551,12 @@ impl StacksBlockBuilder {
         mempool.drop_txs(&invalidated_txs)?;
 
         if let Some(observer) = event_observer {
-            observer.mempool_txs_dropped(invalidated_txs, MemPoolDropReason::TOO_EXPENSIVE);
-            observer.mempool_txs_dropped(to_drop_and_blacklist, MemPoolDropReason::PROBLEMATIC);
+            observer.mempool_txs_dropped(invalidated_txs, None, MemPoolDropReason::TOO_EXPENSIVE);
+            observer.mempool_txs_dropped(
+                to_drop_and_blacklist,
+                None,
+                MemPoolDropReason::PROBLEMATIC,
+            );
         }
 
         if let Err(e) = result {

stackslib/src/core/mempool.rs

@@ -390,7 +390,12 @@ pub trait ProposalCallbackReceiver: Send {
 
 pub trait MemPoolEventDispatcher {
     fn get_proposal_callback_receiver(&self) -> Option<Box<dyn ProposalCallbackReceiver>>;
-    fn mempool_txs_dropped(&self, txids: Vec<Txid>, reason: MemPoolDropReason);
+    fn mempool_txs_dropped(
+        &self,
+        txids: Vec<Txid>,
+        new_txid: Option<Txid>,
+        reason: MemPoolDropReason,
+    );
     fn mined_block_event(
         &self,
         target_burn_height: u64,
@@ -2229,7 +2234,7 @@ impl MemPoolDB {
 
         // broadcast drop event if a tx is being replaced
         if let (Some(prior_tx), Some(event_observer)) = (prior_tx, event_observer) {
-            event_observer.mempool_txs_dropped(vec![prior_tx.txid], replace_reason);
+            event_observer.mempool_txs_dropped(vec![prior_tx.txid], Some(txid), replace_reason);
         };
 
         Ok(())
@@ -2275,7 +2280,7 @@ impl MemPoolDB {
         if let Some(event_observer) = event_observer {
             let sql = "SELECT txid FROM mempool WHERE accept_time < ?1";
             let txids = query_rows(tx, sql, args)?;
-            event_observer.mempool_txs_dropped(txids, MemPoolDropReason::STALE_COLLECT);
+            event_observer.mempool_txs_dropped(txids, None, MemPoolDropReason::STALE_COLLECT);
         }
 
         let sql = "DELETE FROM mempool WHERE accept_time < ?1";
@@ -2297,7 +2302,7 @@ impl MemPoolDB {
         if let Some(event_observer) = event_observer {
             let sql = "SELECT txid FROM mempool WHERE height < ?1";
             let txids = query_rows(tx, sql, args)?;
-            event_observer.mempool_txs_dropped(txids, MemPoolDropReason::STALE_COLLECT);
+            event_observer.mempool_txs_dropped(txids, None, MemPoolDropReason::STALE_COLLECT);
         }
 
         let sql = "DELETE FROM mempool WHERE height < ?1";

stackslib/src/net/api/tests/postblock_proposal.rs

@@ -186,7 +186,13 @@ impl MemPoolEventDispatcher for ProposalTestObserver {
         Some(Box::new(Arc::clone(&self.proposal_observer)))
     }
 
-    fn mempool_txs_dropped(&self, txids: Vec<Txid>, reason: mempool::MemPoolDropReason) {}
+    fn mempool_txs_dropped(
+        &self,
+        txids: Vec<Txid>,
+        new_txid: Option<Txid>,
+        reason: mempool::MemPoolDropReason,
+    ) {
+    }
 
     fn mined_block_event(
         &self,

testnet/stacks-node/src/event_dispatcher.rs

@@ -952,9 +952,14 @@ impl ProposalCallbackReceiver for ProposalCallbackHandler {
 }
 
 impl MemPoolEventDispatcher for EventDispatcher {
-    fn mempool_txs_dropped(&self, txids: Vec<Txid>, reason: MemPoolDropReason) {
+    fn mempool_txs_dropped(
+        &self,
+        txids: Vec<Txid>,
+        new_txid: Option<Txid>,
+        reason: MemPoolDropReason,
+    ) {
         if !txids.is_empty() {
-            self.process_dropped_mempool_txs(txids, reason)
+            self.process_dropped_mempool_txs(txids, new_txid, reason)
         }
     }
 
@@ -1582,7 +1587,12 @@ impl EventDispatcher {
         }
     }
 
-    pub fn process_dropped_mempool_txs(&self, txs: Vec<Txid>, reason: MemPoolDropReason) {
+    pub fn process_dropped_mempool_txs(
+        &self,
+        txs: Vec<Txid>,
+        new_txid: Option<Txid>,
+        reason: MemPoolDropReason,
+    ) {
         // lazily assemble payload only if we have observers
         let interested_observers = self.filter_observers(&self.mempool_observers_lookup, true);
 
@@ -1595,10 +1605,22 @@ impl EventDispatcher {
             .map(|tx| serde_json::Value::String(format!("0x{tx}")))
             .collect();
 
-        let payload = json!({
-            "dropped_txids": serde_json::Value::Array(dropped_txids),
-            "reason": reason.to_string(),
-        });
+        let payload = match new_txid {
+            Some(id) => {
+                json!({
+                    "dropped_txids": serde_json::Value::Array(dropped_txids),
+                    "reason": reason.to_string(),
+                    "new_txid": format!("0x{}", &id),
+                })
+            }
+            None => {
+                json!({
+                    "dropped_txids": serde_json::Value::Array(dropped_txids),
+                    "reason": reason.to_string(),
+                    "new_txid": null,
+                })
+            }
+        };
 
         for observer in interested_observers.iter() {
             observer.send_dropped_mempool_txs(&payload);