fuzz: add transaction broadcast assertions
What the developer wrote
Authored by Joost Jager
fuzz: add transaction broadcast assertions
Add transaction tracking to TestBroadcaster and verify no unexpected
broadcasts occur during normal fuzzing operation:
- Store all broadcast transactions in TestBroadcaster
- Clear the broadcast set after initial channel opens
- Assert in test_return! that no transactions were broadcast
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
What changed, and why it matters
This commit only adds extra checks inside a fuzz test harness. It makes the test's fake transaction broadcaster record any transactions it is asked to broadcast, clears that record after initial channel setup, and then asserts that no further broadcasts happen during normal fuzzing operation. It does not change production code, user-facing behavior, or fix a known bug.
No action required; treat as a normal test-harness improvement. If reviewing, verify the assertion does not make the fuzz target overly restrictive by rejecting legitimate failure-recovery broadcasts.
Security signals we found
Adds an invariant assertion in fuzzing: no unexpected transaction broadcasts during normal operation
Only affects test/fuzz infrastructure, not production consensus or P2P code
No change to cryptographic, networking, or channel-state logic
Evidence from the diff
The change is confined to fuzz/src/chanmon_consistency.rs. TestBroadcaster now stores cloned Transactions in a RefCell
Changed components
fuzz/src/chanmon_consistency.rsTestBroadcaster fuzz mockInspect captured patch +23 / −8
diff --git a/fuzz/src/chanmon_consistency.rs b/fuzz/src/chanmon_consistency.rs
index de83f80..7cc7986 100644
--- a/fuzz/src/chanmon_consistency.rs
+++ b/fuzz/src/chanmon_consistency.rs
@@ -155,9 +155,15 @@ impl MessageRouter for FuzzRouter {
}
}
-pub struct TestBroadcaster {}
+pub struct TestBroadcaster {
+ txn_broadcasted: RefCell<Vec<Transaction>>,
+}
impl BroadcasterInterface for TestBroadcaster {
- fn broadcast_transactions(&self, _txs: &[&Transaction]) {}
+ fn broadcast_transactions(&self, txs: &[&Transaction]) {
+ for tx in txs {
+ self.txn_broadcasted.borrow_mut().push((*tx).clone());
+ }
+ }
}
pub struct VecWriter(pub Vec<u8>);
@@ -334,7 +340,7 @@ impl chain::Watch<TestChannelSigner> for TestChainMonitor {
deserialized_monitor
.update_monitor(
update,
- &&TestBroadcaster {},
+ &&TestBroadcaster { txn_broadcasted: RefCell::new(Vec::new()) },
&&FuzzEstimator { ret_val: atomic::AtomicU32::new(253) },
&self.logger,
)
@@ -604,16 +610,16 @@ fn send_payment(
#[inline]
fn send_hop_noret(
- source: &ChanMan, middle: &ChanMan, middle_scid: u64, dest: &ChanMan, dest_scid: u64,
- amt: u64, payment_ctr: &mut u64,
+ source: &ChanMan, middle: &ChanMan, middle_scid: u64, dest: &ChanMan, dest_scid: u64, amt: u64,
+ payment_ctr: &mut u64,
) {
send_hop_payment(source, middle, middle_scid, dest, dest_scid, amt, payment_ctr);
}
#[inline]
fn send_hop_payment(
- source: &ChanMan, middle: &ChanMan, middle_scid: u64, dest: &ChanMan, dest_scid: u64,
- amt: u64, payment_ctr: &mut u64,
+ source: &ChanMan, middle: &ChanMan, middle_scid: u64, dest: &ChanMan, dest_scid: u64, amt: u64,
+ payment_ctr: &mut u64,
) -> bool {
let (payment_secret, payment_hash) = get_payment_secret_hash(dest, payment_ctr);
let mut payment_id = [0; 32];
@@ -675,7 +681,7 @@ fn send_hop_payment(
#[inline]
pub fn do_test<Out: Output>(data: &[u8], underlying_out: Out, anchors: bool) {
let out = SearchingOutput::new(underlying_out);
- let broadcast = Arc::new(TestBroadcaster {});
+ let broadcast = Arc::new(TestBroadcaster { txn_broadcasted: RefCell::new(Vec::new()) });
let router = FuzzRouter {};
// Read initial monitor styles from fuzz input (1 byte: 2 bits per node)
@@ -1097,6 +1103,10 @@ pub fn do_test<Out: Output>(data: &[u8], underlying_out: Out, anchors: bool) {
let chan_1_id = make_channel!(nodes[0], nodes[1], monitor_a, monitor_b, keys_manager_b, 0);
let chan_2_id = make_channel!(nodes[1], nodes[2], monitor_b, monitor_c, keys_manager_c, 1);
+ // Wipe the transactions-broadcasted set to make sure we don't broadcast any transactions
+ // during normal operation in `test_return`.
+ broadcast.txn_broadcasted.borrow_mut().clear();
+
for node in nodes.iter() {
confirm_txn!(node);
}
@@ -1126,6 +1136,11 @@ pub fn do_test<Out: Output>(data: &[u8], underlying_out: Out, anchors: bool) {
assert_eq!(nodes[0].list_channels().len(), 1);
assert_eq!(nodes[1].list_channels().len(), 2);
assert_eq!(nodes[2].list_channels().len(), 1);
+
+ // At no point should we have broadcasted any transactions after the initial channel
+ // opens.
+ assert!(broadcast.txn_broadcasted.borrow().is_empty());
+
return;
}};
}
Why this scored 12/100
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