Handle all_dbs_active in fabric_doc_update

Previously fabric_doc_update message handler crashed with a function_clause
error the first time it encountered an all_dbs_active error.

Opt to handle it as a `rexi_EXIT` with a hope at that some workers would still
return a valid result.

src/fabric/src/fabric_doc_update.erl

@@ -66,6 +66,11 @@ handle_message({rexi_EXIT, _}, Worker, Acc0) ->
     {WC, LenDocs, W, GrpDocs, DocReplyDict} = Acc0,
     NewGrpDocs = lists:keydelete(Worker, 1, GrpDocs),
     skip_message({WC - 1, LenDocs, W, NewGrpDocs, DocReplyDict});
+handle_message({error, all_dbs_active}, Worker, Acc0) ->
+    % treat it like rexi_EXIT, the hope at least one copy will return successfully
+    {WC, LenDocs, W, GrpDocs, DocReplyDict} = Acc0,
+    NewGrpDocs = lists:keydelete(Worker, 1, GrpDocs),
+    skip_message({WC - 1, LenDocs, W, NewGrpDocs, DocReplyDict});
 handle_message(internal_server_error, Worker, Acc0) ->
     % happens when we fail to load validation functions in an RPC worker
     {WC, LenDocs, W, GrpDocs, DocReplyDict} = Acc0,
@@ -329,6 +334,8 @@ doc_update_test_() ->
             fun doc_update1/0,
             fun doc_update2/0,
             fun doc_update3/0,
+            fun handle_all_dbs_active/0,
+            fun handle_two_all_dbs_actives/0,
             fun one_forbid/0,
             fun two_forbid/0,
             fun extend_tree_forbid/0,
@@ -467,6 +474,65 @@ doc_update3() ->
 
     ?assertEqual({ok, [{Doc1, {ok, Doc1}}, {Doc2, {ok, Doc2}}]}, Reply).
 
+handle_all_dbs_active() ->
+    Doc1 = #doc{revs = {1, [<<"foo">>]}},
+    Doc2 = #doc{revs = {1, [<<"bar">>]}},
+    Docs = [Doc1, Doc2],
+    Shards =
+        mem3_util:create_partition_map("foo", 3, 1, ["node1", "node2", "node3"]),
+    GroupedDocs = group_docs_by_shard_hack(<<"foo">>, Shards, Docs),
+    Acc0 = {
+        length(Shards),
+        length(Docs),
+        list_to_integer("2"),
+        GroupedDocs,
+        dict:from_list([{Doc, []} || Doc <- Docs])
+    },
+
+    {ok, {WaitingCount1, _, _, _, _} = Acc1} =
+        handle_message({ok, [{ok, Doc1}, {ok, Doc2}]}, hd(Shards), Acc0),
+    ?assertEqual(WaitingCount1, 2),
+
+    {ok, {WaitingCount2, _, _, _, _} = Acc2} =
+        handle_message({error, all_dbs_active}, lists:nth(2, Shards), Acc1),
+    ?assertEqual(WaitingCount2, 1),
+
+    {stop, Reply} =
+        handle_message({ok, [{ok, Doc1}, {ok, Doc2}]}, lists:nth(3, Shards), Acc2),
+
+    ?assertEqual({ok, [{Doc1, {ok, Doc1}}, {Doc2, {ok, Doc2}}]}, Reply).
+
+handle_two_all_dbs_actives() ->
+    Doc1 = #doc{revs = {1, [<<"foo">>]}},
+    Doc2 = #doc{revs = {1, [<<"bar">>]}},
+    Docs = [Doc1, Doc2],
+    Shards =
+        mem3_util:create_partition_map("foo", 3, 1, ["node1", "node2", "node3"]),
+    GroupedDocs = group_docs_by_shard_hack(<<"foo">>, Shards, Docs),
+    Acc0 = {
+        length(Shards),
+        length(Docs),
+        list_to_integer("2"),
+        GroupedDocs,
+        dict:from_list([{Doc, []} || Doc <- Docs])
+    },
+
+    {ok, {WaitingCount1, _, _, _, _} = Acc1} =
+        handle_message({ok, [{ok, Doc1}, {ok, Doc2}]}, hd(Shards), Acc0),
+    ?assertEqual(WaitingCount1, 2),
+
+    {ok, {WaitingCount2, _, _, _, _} = Acc2} =
+        handle_message({error, all_dbs_active}, lists:nth(2, Shards), Acc1),
+    ?assertEqual(WaitingCount2, 1),
+
+    {stop, Reply} =
+        handle_message({error, all_dbs_active}, lists:nth(3, Shards), Acc2),
+
+    ?assertEqual(
+        {accepted, [{Doc1, {accepted, Doc1}}, {Doc2, {accepted, Doc2}}]},
+        Reply
+    ).
+
 one_forbid() ->
     Doc1 = #doc{revs = {1, [<<"foo">>]}},
     Doc2 = #doc{revs = {1, [<<"bar">>]}},