From 5c96698de2c1d239985f3c0672b41f29a95ca13c Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Tue, 3 Nov 2026 01:54:10 +0100
Subject: swarm: links by whom we reach

---
 src/simtest/links.rs | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

(limited to 'src/simtest')

diff --git a/src/simtest/links.rs b/src/simtest/links.rs
index 44836bd..17c7ced 100644
--- a/src/simtest/links.rs
+++ b/src/simtest/links.rs
@@ -103,3 +103,51 @@ async fn links_are_relayed_to_members_out_of_reach() {
         .await;
     }
 }
+
+/// a, b and c all on `sim`, but nothing passes between a and c (as behind NAT): once a
+/// judges c unreachable, it asks c's links through b, though it has c's address.
+#[tokio::test(flavor = "multi_thread", worker_threads = 4)]
+async fn links_are_relayed_to_members_that_dont_answer() {
+    let sim = Sim::with_identity(64);
+    let cut = crate::transport::sim::LinkParams {
+        loss: 1.0,
+        ..Default::default()
+    };
+    sim.net.set_link("a", "c", cut.clone());
+    sim.net.set_link("c", "a", cut);
+    let b = sim.start_on("b", &["sim"], &[], Start::Genesis);
+    let a = sim.start_on("a", &["sim"], &["b"], Start::Join);
+    let c = sim.start_on("c", &["sim"], &["b"], Start::Join);
+    sim.wait_ready(&[&a, &b, &c], SOON).await;
+    let (b_id, c_id) = (b.local_id().to_owned(), c.local_id().to_owned());
+    {
+        let (a, c_id) = (&a, c_id.clone());
+        sim.wait_until(
+            "a knows c, and that it doesn't answer",
+            SOON * 3,
+            move || {
+                let c_id = c_id.clone();
+                async move {
+                    let listed = members::members(&a.doc.read().await.doc).contains(&c_id);
+                    listed && a.transport.can_reach(&c_id) && !topology::reaches(a, &c_id).await
+                }
+            },
+        )
+        .await;
+    }
+    links::ask_all(
+        &a,
+        vec![b_id.clone(), c_id.clone()],
+        Duration::from_secs(10),
+    )
+    .await;
+    {
+        let (a, b_id, c_id) = (&a, b_id.clone(), c_id.clone());
+        sim.wait_until("a has c's links, relayed by b", SOON, move || {
+            let (b_id, c_id) = (b_id.clone(), c_id.clone());
+            async move { has_links(a, &c_id, &b_id) }
+        })
+        .await;
+    }
+    assert!(!c.links.subscribers().contains(&a.local_id().to_owned()));
+}
-- 
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