Add an option to dead-letter rejected publishes

Add `reject-publish-dlx` overflow strategy, which is similar to
`reject-publish` strategy, but also dead-letters rejected messages.

Closes #1443

4 files changed, 52 insertions, 6 deletions

diff --git a/src/rabbit_amqqueue.erl b/src/rabbit_amqqueue.erl
index 9e94dd8f27..85c647ae8c 100644
--- a/src/rabbit_amqqueue.erl
+++ b/src/rabbit_amqqueue.erl
@@ -761,7 +761,9 @@ check_dlxrk_arg({Type,    _}, _Args) ->
     {error, {unacceptable_type, Type}}.
 
 check_overflow({longstr, Val}, _Args) ->
-    case lists:member(Val, [<<"drop-head">>, <<"reject-publish">>]) of
+    case lists:member(Val, [<<"drop-head">>,
+                            <<"reject-publish">>,
+                            <<"reject-publish-dlx">>]) of
         true  -> ok;
         false -> {error, invalid_overflow}
     end;
diff --git a/src/rabbit_amqqueue_process.erl b/src/rabbit_amqqueue_process.erl
index b3f89b7ef0..2666847e77 100644
--- a/src/rabbit_amqqueue_process.erl
+++ b/src/rabbit_amqqueue_process.erl
@@ -82,7 +82,7 @@
             %% max length in bytes, if configured
             max_bytes,
             %% an action to perform if queue is to be over a limit,
-            %% can be either drop-head (default) or reject-publish
+            %% can be either drop-head (default), reject-publish or reject-publish-dlx
             overflow,
             %% when policies change, this version helps queue
             %% determine what previously scheduled/set up state to ignore,
@@ -704,12 +704,25 @@ maybe_deliver_or_enqueue(Delivery = #delivery{message = Message},
                          Delivered,
                          State = #q{overflow            = Overflow,
                                     backing_queue       = BQ,
-                                    backing_queue_state = BQS}) ->
+                                    backing_queue_state = BQS,
+                                    dlx                 = DLX,
+                                    dlx_routing_key     = RK}) ->
     send_mandatory(Delivery), %% must do this before confirms
     case {will_overflow(Delivery, State), Overflow} of
         {true, 'reject-publish'} ->
             %% Drop publish and nack to publisher
             send_reject_publish(Delivery, Delivered, State);
+        {true, 'reject-publish-dlx'} ->
+            %% Publish to DLX
+            with_dlx(
+              DLX,
+              fun (X) ->
+                      QName = qname(State),
+                      rabbit_dead_letter:publish(Message, maxlen, X, RK, QName)
+              end,
+              fun () -> ok end),
+            %% Drop publish and nack to publisher
+            send_reject_publish(Delivery, Delivered, State);
         _ ->
             {IsDuplicate, BQS1} = BQ:is_duplicate(Message, BQS),
             State1 = State#q{backing_queue_state = BQS1},
@@ -766,6 +779,8 @@ maybe_drop_head(State = #q{max_length = undefined,
     {false, State};
 maybe_drop_head(State = #q{overflow = 'reject-publish'}) ->
     {false, State};
+maybe_drop_head(State = #q{overflow = 'reject-publish-dlx'}) ->
+    {false, State};
 maybe_drop_head(State = #q{overflow = 'drop-head'}) ->
     maybe_drop_head(false, State).
 
diff --git a/src/rabbit_policies.erl b/src/rabbit_policies.erl
index 7878bed02d..c4f4226448 100644
--- a/src/rabbit_policies.erl
+++ b/src/rabbit_policies.erl
@@ -131,6 +131,8 @@ validate_policy0(<<"overflow">>, <<"drop-head">>) ->
     ok;
 validate_policy0(<<"overflow">>, <<"reject-publish">>) ->
     ok;
+validate_policy0(<<"overflow">>, <<"reject-publish-dlx">>) ->
+    ok;
 validate_policy0(<<"overflow">>, Value) ->
     {error, "~p is not a valid overflow value", [Value]};
 
diff --git a/test/dead_lettering_SUITE.erl b/test/dead_lettering_SUITE.erl
index 6fe2a3a522..fe5e91c8ed 100644
--- a/test/dead_lettering_SUITE.erl
+++ b/test/dead_lettering_SUITE.erl
@@ -60,13 +60,15 @@ groups() ->
      {dead_letter_tests, [],
       [
        {classic_queue, [parallel], DeadLetterTests ++ [dead_letter_ttl,
+                                                       dead_letter_max_length_reject_publish_dlx,
                                                        dead_letter_routing_key_cycle_ttl,
                                                        dead_letter_headers_reason_expired,
                                                        dead_letter_headers_reason_expired_per_message]},
        {mirrored_queue, [parallel], DeadLetterTests ++ [dead_letter_ttl,
-                                                       dead_letter_routing_key_cycle_ttl,
-                                                       dead_letter_headers_reason_expired,
-                                                       dead_letter_headers_reason_expired_per_message]},
+                                                        dead_letter_max_length_reject_publish_dlx,
+                                                        dead_letter_routing_key_cycle_ttl,
+                                                        dead_letter_headers_reason_expired,
+                                                        dead_letter_headers_reason_expired_per_message]},
        {quorum_queue, [parallel], DeadLetterTests}
       ]}
     ].
@@ -381,6 +383,31 @@ dead_letter_max_length_drop_head(Config) ->
     _ = consume(Ch, DLXQName, [P1, P2]),
     consume_empty(Ch, DLXQName).
 
+%% Another strategy: reject-publish-dlx
+dead_letter_max_length_reject_publish_dlx(Config) ->
+    {_Conn, Ch} = rabbit_ct_client_helpers:open_connection_and_channel(Config, 0),
+    QName = ?config(queue_name, Config),
+    DLXQName = ?config(queue_name_dlx, Config),
+
+    declare_dead_letter_queues(Ch, Config, QName, DLXQName,
+                               [{<<"x-max-length">>, long, 1},
+                                {<<"x-overflow">>, longstr, <<"reject-publish-dlx">>}]),
+
+    P1 = <<"msg1">>,
+    P2 = <<"msg2">>,
+    P3 = <<"msg3">>,
+
+    %% Publish 3 messages
+    publish(Ch, QName, [P1, P2, P3]),
+    %% Consume the first one from the queue (max-length = 1)
+    wait_for_messages(Config, [[QName, <<"1">>, <<"1">>, <<"0">>]]),
+    _ = consume(Ch, QName, [P1]),
+    consume_empty(Ch, QName),
+    %% Consume the dropped ones from the dead letter queue
+    wait_for_messages(Config, [[DLXQName, <<"2">>, <<"2">>, <<"0">>]]),
+    _ = consume(Ch, DLXQName, [P2, P3]),
+    consume_empty(Ch, DLXQName).
+
 %% Dead letter exchange does not have to be declared when the queue is declared, but it should
 %% exist by the time messages need to be dead-lettered; if it is missing then, the messages will
 %% be silently dropped.