From 7d923ee5702dfb3d4a96a541667b82206cf8b0e3 Mon Sep 17 00:00:00 2001
From: Luke Bakken <lrbakken@amazon.com>
Date: Mon, 15 Dec 2025 18:55:55 -0800
Subject: [PATCH] Return friendly error when AMQP 1.0 receiver has no source

When a client attaches an AMQP 1.0 receiver link without specifying a
source address, RabbitMQ crashes with a `function_clause` error and
returns an Erlang stack trace to the client. This makes it difficult for
developers to understand what went wrong.

Previously, the client received:
```
SessionError: function_clause
[{rabbit_amqp_session,ensure_source,
     [undefined,false,<<...>>,<<...>>,
      {user,<<...>>,[administrator],[...]},
      <<...>>,<0.585.0>,[],[]],
     [{file,"rabbit_amqp_session.erl"},{line,2665}]},
 {rabbit_amqp_session,handle_attach,2,...},
 ...]
```

This change adds a new clause to `ensure_source/9` that catches the case
where the source is `undefined`. Instead of crashing, the function now
returns `{error, source_address_required}`, which `handle_attach/2` maps
to an `amqp:invalid-field` error with a clear message.

Now, the client receives:
```
LinkError: Attach refused: source_address_required
  condition: 'amqp:invalid-field',
  description: 'Attach refused: source_address_required'
```

The error condition `amqp:invalid-field` is appropriate here because the
client failed to provide a required field in the attach frame, not
because a resource was not found.

Also added a test for an `undefined` receiver address.

Fixes https://github.com/rabbitmq/rabbitmq-server/discussions/14300
---
 deps/rabbit/src/rabbit_amqp_session.erl |  2 ++
 deps/rabbit/test/amqp_address_SUITE.erl | 36 ++++++++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/deps/rabbit/src/rabbit_amqp_session.erl b/deps/rabbit/src/rabbit_amqp_session.erl
index f178c9a51c5d..6bc0075d1473 100644
--- a/deps/rabbit/src/rabbit_amqp_session.erl
+++ b/deps/rabbit/src/rabbit_amqp_session.erl
@@ -2719,6 +2719,8 @@ ensure_source(#'v1_0.source'{
         _ ->
             exit_not_implemented("Dynamic source not supported: ~tp", [Source0])
     end;
+ensure_source(undefined, _, _, _, _, _, _, _, _) ->
+    {error, source_required};
 ensure_source(Source = #'v1_0.source'{dynamic = true}, _, _, _, _, _, _, _, _) ->
     exit_not_implemented("Dynamic source not supported: ~tp", [Source]);
 ensure_source(Source0 = #'v1_0.source'{address = Address,
diff --git a/deps/rabbit/test/amqp_address_SUITE.erl b/deps/rabbit/test/amqp_address_SUITE.erl
index 50adfa8a9344..a08c15b5526a 100644
--- a/deps/rabbit/test/amqp_address_SUITE.erl
+++ b/deps/rabbit/test/amqp_address_SUITE.erl
@@ -65,7 +65,8 @@ common_tests() ->
      target_per_message_exchange_absent_settled,
      target_per_message_exchange_absent_unsettled,
      target_bad_address,
-     source_bad_address
+     source_bad_address,
+     receiver_address_undefined
     ].
 
 init_per_suite(Config) ->
@@ -420,6 +421,39 @@ target_per_message_unset_to_address(Config) ->
     ok = amqp10_client:end_session(Session),
     ok = amqp10_client:close_connection(Connection).
 
+%% Test v2 target address
+%% receiver address undefined
+receiver_address_undefined(Config) ->
+    QName = atom_to_binary(?FUNCTION_NAME),
+    Addr = rabbitmq_amqp_address:queue(QName),
+    Init = {_, LinkPair = #link_pair{session = Session}} = init(Config),
+    {ok, _} = rabbitmq_amqp_client:declare_queue(LinkPair, QName, #{}),
+
+    AttachArgs = #{name => <<"receiver">>,
+                   role => {receiver, #{address => undefined,
+                                        durable => none}, self()},
+                   snd_settle_mode => settled,
+                   rcv_settle_mode => first,
+                   filter => #{},
+                   properties => #{},
+                   raw_mode => false},
+    {ok, Receiver} = amqp10_client:attach_link(Session, AttachArgs),
+
+    Expected = {amqp10_event, {link, Receiver, {detached, #'v1_0.error'{
+                                                             condition = ?V_1_0_AMQP_ERROR_INVALID_FIELD,
+                                                             description = {utf8, <<"Attach refused: {bad_address,undefined}">>}}}}},
+    Got = receive
+              {amqp10_event, {link, _, {detached, _}}}=Event ->
+                  Event
+          after ?TIMEOUT ->
+                    Reason = {missing_event, ?LINE},
+                    flush(Reason),
+                    ct:fail(Reason)
+          end,
+    ?assertMatch(Got, Expected),
+    {ok, _} = rabbitmq_amqp_client:delete_queue(LinkPair, QName),
+    ok = cleanup(Init).
+
 bad_v2_addresses() ->
     [
      %% valid v1, but bad v2 target addresses