From 0199d11c381b0d6ad59026409a80337b060081a2 Mon Sep 17 00:00:00 2001
From: Michael Klishin <klishinm@vmware.com>
Date: Mon, 26 Oct 2020 18:50:07 +0300
Subject: [PATCH] Merge pull request #150 from rabbitmq/binding-recovery-fix

Explicitly recover binding on plugin init

(cherry picked from commit 4d838f3159b6dffa4ccf447b1f5054258039f7b2)
---
 src/rabbit_delayed_message.erl | 45 +++++++++++++++++++++++++++++++++-
 1 file changed, 44 insertions(+), 1 deletion(-)

diff --git a/src/rabbit_delayed_message.erl b/src/rabbit_delayed_message.erl
index c3943ef..69e2624 100644
--- a/src/rabbit_delayed_message.erl
+++ b/src/rabbit_delayed_message.erl
@@ -13,7 +13,7 @@
 %% https://www.erlang.org/documentation/doc-7.0-rc1/erts-7.0/doc/html/time_correction.html
 
 -module(rabbit_delayed_message).
-
+-include_lib("rabbit_common/include/rabbit.hrl").
 -rabbit_boot_step({?MODULE,
                    [{description, "exchange delayed message mnesia setup"},
                     {mfa, {?MODULE, setup_mnesia, []}},
@@ -106,6 +106,7 @@ messages_delayed(Exchange) ->
 %%--------------------------------------------------------------------
 
 init([]) ->
+    recover(),
     {ok, #state{timer = not_set}}.
 
 handle_call({delay_message, Exchange, Delivery, Delay},
@@ -216,3 +217,45 @@ append_to_atom(Atom, Append) when is_atom(Append) ->
     append_to_atom(Atom, atom_to_list(Append));
 append_to_atom(Atom, Append) when is_list(Append) ->
     list_to_atom(atom_to_list(Atom) ++ Append).
+
+recover() ->
+    %% topology recovery has already happened, we have to recover state for any durable
+    %% consistent hash exchanges since plugin activation was moved later in boot process
+    %% starting with RabbitMQ 3.8.4
+    case list_exchanges() of
+        {ok, Xs} ->
+            rabbit_log:debug("Delayed message exchange: "
+                              "have ~b durable exchanges to recover",
+                             [length(Xs)]),
+            [recover_exchange_and_bindings(X) || X <- lists:usort(Xs)];
+        {aborted, Reason} ->
+            rabbit_log:error(
+                "Delayed message exchange: "
+                 "failed to recover durable bindings of one of the exchanges, reason: ~p",
+                [Reason])
+    end.
+
+list_exchanges() ->
+    case mnesia:transaction(
+           fun () ->
+                   mnesia:match_object(
+                     rabbit_exchange, #exchange{durable = true,
+                                                type = 'x-delayed-message',
+                                                _ = '_'}, write)
+           end) of
+        {atomic, Xs} ->
+            {ok, Xs};
+        {aborted, Reason} ->
+            {aborted, Reason}
+    end.
+
+recover_exchange_and_bindings(#exchange{name = XName} = X) ->
+    mnesia:transaction(
+        fun () ->
+            Bindings = rabbit_binding:list_for_source(XName),
+            [rabbit_exchange_type_delayed_message:add_binding(transaction, X, B)
+             || B <- lists:usort(Bindings)],
+            rabbit_log:debug("Delayed message exchange: "
+                              "recovered bindings for ~s",
+                             [rabbit_misc:rs(XName)])
+    end).