From bbbe9713cdc504da0a6a3780cad97dfe696f5170 Mon Sep 17 00:00:00 2001
From: Kenneth Giusti <kgiusti@redhat.com>
Date: Fri, 24 Jan 2025 09:13:27 -0500
Subject: [PATCH] Fixes #1720: flush all incoming AMQP messages on connection
 drop

---
 src/adaptors/amqp/amqp_adaptor.c | 48 ++++++++++++++++++++------------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/src/adaptors/amqp/amqp_adaptor.c b/src/adaptors/amqp/amqp_adaptor.c
index 78e12592b..f3cb032a6 100644
--- a/src/adaptors/amqp/amqp_adaptor.c
+++ b/src/adaptors/amqp/amqp_adaptor.c
@@ -1202,41 +1202,50 @@ static int AMQP_link_flow_handler(qd_router_t *router, qd_link_t *link)
 }
 
 
-/**
- * Link Detached Handler
+/** Pull any pending incoming messages off the link and forward them
+ *
+ * (DISPATCH-1085): When Proton indicates that an incoming link has detached OR the parent connection/session of the link
+ * has abruptly closed (link has not cleanly detached) there may still be incoming messages buffered on the link that
+ * need to be processed. This helper function attempts to read all buffered messages and forward them.
  */
-static int AMQP_link_detach_handler(qd_router_t *router, qd_link_t *link)
+static void drain_link(qd_router_t *router, qd_link_t *qd_link)
 {
-    assert(link);
-
-    pn_link_t *pn_link = qd_link_pn(link);
-    if (!pn_link)
-        return 0;
-
-    // DISPATCH-1085: If link is in the middle of receiving a message it is
-    // possible that the message is actually complete but the remaining message
-    // data is still in proton's buffers.  (e.g. a large message is sent then
-    // the sender immediately detaches) Force a call to the rx_handler for the
-    // link in order to pull the buffered data into the message.
-    if (pn_link_is_receiver(pn_link)) {
+    pn_link_t *pn_link = qd_link_pn(qd_link);
+    if (!!pn_link && pn_link_is_receiver(pn_link)) {
         pn_delivery_t *pnd = pn_link_current(pn_link);
         if (pnd) {
             qd_message_t *msg = qd_get_message_context(pnd);
             if (msg) {
                 if (!qd_message_receive_complete(msg)) {
-                    qd_link_set_q2_limit_unbounded(link, true);
+                    qd_link_set_q2_limit_unbounded(qd_link, true);
 
                     // since this thread owns link we can call the
                     // rx_hander directly rather than schedule it via
                     // the unblock handler:
                     qd_message_clear_q2_unblocked_handler(msg);
                     qd_message_Q2_holdoff_disable(msg);
-                    while (AMQP_rx_handler(router, link))
+                    while (AMQP_rx_handler(router, qd_link))
                            ;
                 }
             }
         }
     }
+}
+
+
+/**
+ * Link Detached Handler
+ */
+static int AMQP_link_detach_handler(qd_router_t *router, qd_link_t *link)
+{
+    assert(link);
+
+    pn_link_t *pn_link = qd_link_pn(link);
+    if (!pn_link)
+        return 0;
+
+    // attempt to forward any remaining pending messages
+    drain_link(router, link);
 
     // Notify the core that a detach has been received.
 
@@ -1265,6 +1274,9 @@ static void AMQP_link_closed_handler(qd_router_t *router, qd_link_t *qd_link, bo
 {
     assert(qd_link);
 
+    // attempt to forward any remaining pending messages
+    drain_link(router, qd_link);
+
     // Clean up all qdr_delivery/pn_delivery bindings for the link.
 
     qd_link_ref_list_t *list = qd_link_get_ref_list(qd_link);
@@ -1277,7 +1289,7 @@ static void AMQP_link_closed_handler(qd_router_t *router, qd_link_t *qd_link, bo
 
         // This will decrement the qdr_delivery_t reference count - do not access the dlv pointer after this call!
         qdr_node_disconnect_deliveries(router->router_core, qd_link, dlv, pdlv);
-        ref = DEQ_HEAD(*list);
+        ref = DEQ_HEAD(*list);  // disconnecting the delivery removes ref from the list and frees it
     }
 
     qdr_link_t *qdr_link = (qdr_link_t *) qd_link_get_context(qd_link);