Store a SyncStatus handle in the Crawler

The helper type will make it easier to determine if the crawler is
enabled or not.

zebrad/src/commands/start.rs

@@ -85,12 +85,12 @@ impl StartCmd {
 
         info!("initializing syncer");
         // TODO: use sync_status to activate the mempool (#2592)
-        let (syncer, _sync_status) =
+        let (syncer, sync_status) =
             ChainSync::new(&config, peer_set.clone(), state, chain_verifier);
 
         select! {
             result = syncer.sync().fuse() => result,
-            _ = mempool::Crawler::spawn(peer_set).fuse() => {
+            _ = mempool::Crawler::spawn(peer_set, sync_status).fuse() => {
                 unreachable!("The mempool crawler only stops if it panics");
             }
         }

zebrad/src/components/mempool/crawler.rs

@@ -10,6 +10,8 @@ use tower::{timeout::Timeout, BoxError, Service, ServiceExt};
 
 use zebra_network::{Request, Response};
 
+use super::super::sync::SyncStatus;
+
 #[cfg(test)]
 mod tests;
 
@@ -31,6 +33,7 @@ const PEER_RESPONSE_TIMEOUT: Duration = Duration::from_secs(6);
 /// The mempool transaction crawler.
 pub struct Crawler<S> {
     peer_set: Mutex<Timeout<S>>,
+    status: SyncStatus,
 }
 
 impl<S> Crawler<S>
@@ -39,9 +42,10 @@ where
     S::Future: Send,
 {
     /// Spawn an asynchronous task to run the mempool crawler.
-    pub fn spawn(peer_set: S) -> JoinHandle<Result<(), BoxError>> {
+    pub fn spawn(peer_set: S, status: SyncStatus) -> JoinHandle<Result<(), BoxError>> {
         let crawler = Crawler {
             peer_set: Mutex::new(Timeout::new(peer_set, PEER_RESPONSE_TIMEOUT)),
+            status,
         };
 
         tokio::spawn(crawler.run())

zebrad/src/components/mempool/crawler/tests.rs

@@ -8,7 +8,7 @@ use tower::{buffer::Buffer, util::BoxService, BoxError};
 
 use zebra_network::{Request, Response};
 
-use super::{Crawler, FANOUT, RATE_LIMIT_DELAY};
+use super::{Crawler, SyncStatus, FANOUT, RATE_LIMIT_DELAY};
 
 /// The number of iterations to crawl while testing.
 ///
@@ -30,7 +30,13 @@ const ERROR_MARGIN: Duration = Duration::from_millis(100);
 async fn crawler_requests_for_transaction_ids() {
     let (peer_set, mut requests) = mock_peer_set();
 
-    Crawler::spawn(peer_set);
+    // Mock the latest sync length in a state that enables the mempool.
+    let (sync_status, mut recent_sync_lengths) = SyncStatus::new();
+    for _ in 0..5 {
+        recent_sync_lengths.push_extend_tips_length(0);
+    }
+
+    Crawler::spawn(peer_set, sync_status);
 
     time::pause();