From 516a97115bc064422e7b2c52cc73565b0c0600da Mon Sep 17 00:00:00 2001
From: David Ansari <david.ansari@gmx.de>
Date: Tue, 27 Feb 2024 10:50:38 +0100
Subject: [PATCH] Fix AMQP 0.9.1 headers regression

Fixes https://github.com/rabbitmq/rabbitmq-server/discussions/10620

Up to RabbitMQ 3.12:
* When an AMQP 0.9.1 publisher sends a message with P_basic.headers
  unset, RabbitMQ will deliver an AMQP 0.9.1 message with
  P_basic.headers unset.
* When an AMQP 0.9.1 publisher sends a message with P_basic.headers
  being an empty list ([]), RabbitMQ will deliver an AMQP 0.9.1 message with
  P_basic.headers being an empty list ([]).

In 3.13 including message containers, the 1st behaviour stayed the same
while the 2nd behaviour changed to:
* When an AMQP 0.9.1 publisher sends a message with P_basic.headers
  being an empty list ([]), RabbitMQ will deliver an AMQP 0.9.1 message with
  P_basic.headers unset.

This commit fixes this regression by using the same behaviour as in
3.12.

(cherry picked from commit 8a2a7406de68daca397f0d6503070b51f4c53a6e)
---
 deps/rabbit/src/mc_amqpl.erl            |  2 +-
 deps/rabbit/test/quorum_queue_SUITE.erl | 36 +++++++++++++++++++++++--
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/deps/rabbit/src/mc_amqpl.erl b/deps/rabbit/src/mc_amqpl.erl
index 5a6a65a3b5fb..23e7802a81ad 100644
--- a/deps/rabbit/src/mc_amqpl.erl
+++ b/deps/rabbit/src/mc_amqpl.erl
@@ -412,7 +412,7 @@ protocol_state(#content{properties = #'P_basic'{headers = H00} = B0} = C,
                  end, Headers0, Anns),
     Headers = case Headers1 of
                   [] ->
-                      undefined;
+                      H00;
                   _ ->
                       %% Dedup
                       lists:usort(fun({Key1, _, _}, {Key2, _, _}) ->
diff --git a/deps/rabbit/test/quorum_queue_SUITE.erl b/deps/rabbit/test/quorum_queue_SUITE.erl
index 4bfc3d0f06b1..0aa68d222857 100644
--- a/deps/rabbit/test/quorum_queue_SUITE.erl
+++ b/deps/rabbit/test/quorum_queue_SUITE.erl
@@ -166,8 +166,8 @@ all_tests() ->
      consumer_priorities,
      cancel_consumer_gh_3729,
      cancel_and_consume_with_same_tag,
-     validate_messages_on_queue
-
+     validate_messages_on_queue,
+     amqpl_headers
     ].
 
 memory_tests() ->
@@ -3332,6 +3332,38 @@ validate_messages_on_queue(Config) ->
 
     ok.
 
+amqpl_headers(Config) ->
+    [Server | _] = Servers = rabbit_ct_broker_helpers:get_node_configs(Config, nodename),
+    Ch = rabbit_ct_client_helpers:open_channel(Config, Server),
+    QQ = ?config(queue_name, Config),
+    ?assertEqual({'queue.declare_ok', QQ, 0, 0},
+                 declare(Ch, QQ, [{<<"x-queue-type">>, longstr, <<"quorum">>}])),
+
+    Headers1Sent = undefined,
+    Headers2Sent = [],
+    [ok = amqp_channel:cast(
+            Ch,
+            #'basic.publish'{routing_key = QQ},
+            #amqp_msg{props = #'P_basic'{headers = HeadersSent,
+                                         delivery_mode = 2}}) ||
+     HeadersSent <- [Headers1Sent, Headers2Sent]],
+    RaName = ra_name(QQ),
+    wait_for_messages_ready(Servers, RaName, 2),
+
+    {#'basic.get_ok'{},
+     #amqp_msg{props = #'P_basic'{headers = Headers1Received}}
+    } = amqp_channel:call(Ch, #'basic.get'{queue = QQ}),
+
+    {#'basic.get_ok'{delivery_tag = DeliveryTag},
+     #amqp_msg{props = #'P_basic'{headers = Headers2Received}}
+    } = amqp_channel:call(Ch, #'basic.get'{queue = QQ}),
+
+    ?assertEqual(Headers1Sent, Headers1Received),
+    ?assertEqual(Headers2Sent, Headers2Received),
+
+    ok = amqp_channel:cast(Ch, #'basic.ack'{delivery_tag = DeliveryTag,
+                                            multiple = true}).
+
 leader_locator_client_local(Config) ->
     [Server1 | _] = Servers = rabbit_ct_broker_helpers:get_node_configs(Config, nodename),
     Q = ?config(queue_name, Config),