[Tarantool-patches] [PATCH] replication: list anonymous replicas in box.info.replication

[Serge Petrenko]

Closes #4900

@TarantoolBot document
Title: Enrich box.info.replication output with anonymous replicas

A new field is added to replica info in `box.info.replication` output:
`anon`. The field is boolean and set to `true` for anonymous replicas
and to `false` for normal replicas.

Also now anonymous replicas are listed in `box.info.replication`
together with normal ones, so it's easier to track their connection
state. Anonymous replicas occupy table slots past the biggest-id normal
replica. Example:
```
...
  replication:
    1:
      id: 1
      uuid: 326eb713-1b79-4b43-9b48-661314260c61
      lsn: 4
      anon: false
    2:
      id: 0
      uuid: 869aa6d8-7e78-488c-945d-ff5ef8cf8a42
      lsn: 0
      downstream:
        status: follow
        idle: 0.4463420000011
        vclock: {1: 4}
      anon: true
...
```

Note, that anonymous replicas hide their lsn from the others, so
anonymous replica lsn will always be reported as zero, even if anonymous
replicas perform some local space operations.
To know the anonymous replica's lsn, you have to issue `box.info.lsn` on
it.
---
https://github.com/tarantool/tarantool/issues/4900
https://github.com/tarantool/tarantool/tree/sp/gh-4900-list-anon-replicas

@ChangeLog
  - Start listing anonymous replicas in `box.info.replication`
    and add `anon` field to each replica output.
    Anonymous replicas are listed after all the normal replicas.
    (gh-4900)

 src/box/lua/info.c             | 20 ++++++++++++++++++++
 test/replication/anon.result   | 12 ++++++++++--
 test/replication/anon.test.lua |  4 +++-
 3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/src/box/lua/info.c b/src/box/lua/info.c
index a789f7822..5c07c91a9 100644
--- a/src/box/lua/info.c
+++ b/src/box/lua/info.c
@@ -169,6 +169,10 @@ lbox_pushreplica(lua_State *L, struct replica *replica)
 	lua_pushinteger(L, replica->id);
 	lua_settable(L, -3);
 
+	lua_pushstring(L, "anon");
+	lua_pushboolean(L, replica->anon);
+	lua_settable(L, -3);
+
 	lua_pushstring(L, "uuid");
 	lua_pushstring(L, tt_uuid_str(&replica->uuid));
 	lua_settable(L, -3);
@@ -201,6 +205,11 @@ lbox_info_replication(struct lua_State *L)
 	lua_setfield(L, -2, "__serialize");
 	lua_setmetatable(L, -2);
 
+	/*
+	 * A counter to start enumerating anonymous replicas after
+	 * all the other ones.
+	 */
+	uint32_t max_id = 0;
 	replicaset_foreach(replica) {
 		/* Applier hasn't received replica id yet */
 		if (replica->id == REPLICA_ID_NIL)
@@ -209,6 +218,17 @@ lbox_info_replication(struct lua_State *L)
 		lbox_pushreplica(L, replica);
 
 		lua_rawseti(L, -2, replica->id);
+		if (replica->id > max_id)
+			max_id = replica->id;
+	}
+
+	replicaset_foreach(replica) {
+		if (!replica->anon)
+			continue;
+
+		lbox_pushreplica(L, replica);
+
+		lua_rawseti(L, -2, ++max_id);
 	}
 
 	return 1;
diff --git a/test/replication/anon.result b/test/replication/anon.result
index cbbeeef09..6f907f614 100644
--- a/test/replication/anon.result
+++ b/test/replication/anon.result
@@ -151,10 +151,18 @@ test_run:cmd('switch default')
  | - true
  | ...
 
--- Replica isn't visible on master.
+-- Anonymous replicas are shown in master's box.info.replication.
 #box.info.replication
  | ---
- | - 1
+ | - 2
+ | ...
+box.info.replication[2].anon
+ | ---
+ | - true
+ | ...
+box.info.replication[2].downstream.status
+ | ---
+ | - follow
  | ...
 
 -- Test that replication (even anonymous) from an anonymous
diff --git a/test/replication/anon.test.lua b/test/replication/anon.test.lua
index 627dc5c8e..3a6756342 100644
--- a/test/replication/anon.test.lua
+++ b/test/replication/anon.test.lua
@@ -50,8 +50,10 @@ box.space.loc:truncate()
 
 test_run:cmd('switch default')
 
--- Replica isn't visible on master.
+-- Anonymous replicas are shown in master's box.info.replication.
 #box.info.replication
+box.info.replication[2].anon
+box.info.replication[2].downstream.status
 
 -- Test that replication (even anonymous) from an anonymous
 -- instance is forbidden. An anonymous replica will fetch
-- 
2.21.1 (Apple Git-122.3)