tProxy: unbounded central downstream queue allows remote memory exhaustion

[GitGab19]

Proof of Concept

diff --git a/miner-apps/translator/src/lib/sv1/sv1_server/mod.rs b/miner-apps/translator/src/lib/sv1/sv1_server/mod.rs
--- a/miner-apps/translator/src/lib/sv1/sv1_server/mod.rs
+++ b/miner-apps/translator/src/lib/sv1/sv1_server/mod.rs
@@ -1694,5 +1694,33 @@ mod tests {
         let seq_id = server.sequence_counter.fetch_add(1, Ordering::SeqCst);
         assert_eq!(seq_id, 1);
         assert_eq!(server.sequence_counter.load(Ordering::SeqCst), 2);
     }
+
+    #[test]
+    fn test_downstream_to_server_queue_applies_backpressure() {
+        use stratum_apps::stratum_core::sv1_api::json_rpc;
+
+        let server = create_test_sv1_server();
+        let message = json_rpc::Message::StandardRequest(json_rpc::StandardRequest {
+            id: 1,
+            method: "mining.subscribe".to_string(),
+            params: serde_json::Value::Null,
+        });
+
+        const N: usize = 50_000;
+        let accepted = (0..N)
+            .filter(|_| {
+                server
+                    .sv1_server_io
+                    .downstream_to_sv1_server_sender
+                    .try_send((1, message.clone()))
+                    .is_ok()
+            })
+            .count();
+
+        assert!(
+            accepted < N,
+            "downstream_to_sv1_server queue accepted all {accepted} messages without backpressure"
+        );
+    }
 }