replication: show errno in replication info

Box.info.replication shows applier/relay's latest error message.
But it didn't include errno description for system errors, even
though it was included in the logs. Now box.info shows the errno
description as well, when possible.

Closes #4402

Conflicts:
	test/replication/suite.cfg

src/box/lua/info.c

@@ -50,6 +50,7 @@
 #include "box/box.h"
 #include "lua/utils.h"
 #include "fiber.h"
+#include "tt_static.h"
 
 static void
 lbox_pushvclock(struct lua_State *L, const struct vclock *vclock)
@@ -65,6 +66,20 @@ lbox_pushvclock(struct lua_State *L, const struct vclock *vclock)
 	luaL_setmaphint(L, -1); /* compact flow */
 }
 
+static inline void
+lbox_push_replication_error_message(struct lua_State *L, struct error *e,
+				    int idx)
+{
+	lua_pushstring(L, "message");
+	lua_pushstring(L, e->errmsg);
+	lua_settable(L, idx - 2);
+	if (e->saved_errno == 0)
+		return;
+	lua_pushstring(L, "system_message");
+	lua_pushstring(L, strerror(e->saved_errno));
+	lua_settable(L, idx - 2);
+}
+
 static void
 lbox_pushapplier(lua_State *L, struct applier *applier)
 {
@@ -103,11 +118,8 @@ lbox_pushapplier(lua_State *L, struct applier *applier)
 		lua_settable(L, -3);
 
 		struct error *e = diag_last_error(&applier->reader->diag);
-		if (e != NULL) {
-			lua_pushstring(L, "message");
-			lua_pushstring(L, e->errmsg);
-			lua_settable(L, -3);
-		}
+		if (e != NULL)
+			lbox_push_replication_error_message(L, e, -1);
 	}
 }
 
@@ -135,11 +147,8 @@ lbox_pushrelay(lua_State *L, struct relay *relay)
 		lua_settable(L, -3);
 
 		struct error *e = diag_last_error(relay_get_diag(relay));
-		if (e != NULL) {
-			lua_pushstring(L, "message");
-			lua_pushstring(L, e->errmsg);
-			lua_settable(L, -3);
-		}
+		if (e != NULL)
+			lbox_push_replication_error_message(L, e, -1);
 		break;
 	}
 	default: unreachable();

test/replication/gh-4402-info-errno.result

+-- test-run result file version 2
+test_run = require('test_run').new()
+ | ---
+ | ...
+
+--
+-- gh-4402: replication info table should contain not only
+-- Tarantool's error, but also a system error (errno's message)
+-- when possible.
+--
+
+box.schema.user.grant('guest', 'replication')
+ | ---
+ | ...
+
+test_run:cmd('create server replica with rpl_master=default, script="replication/replica.lua"')
+ | ---
+ | - true
+ | ...
+test_run:cmd('start server replica')
+ | ---
+ | - true
+ | ...
+i = box.info
+ | ---
+ | ...
+replica_id = i.id % 2 + 1
+ | ---
+ | ...
+d = i.replication[replica_id].downstream
+ | ---
+ | ...
+d ~= nil and d.status == 'follow' or i
+ | ---
+ | - true
+ | ...
+
+test_run:cmd('stop server replica')
+ | ---
+ | - true
+ | ...
+test_run:cmd("cleanup server replica")
+ | ---
+ | - true
+ | ...
+test_run:cmd("delete server replica")
+ | ---
+ | - true
+ | ...
+i = box.info
+ | ---
+ | ...
+d = i.replication[replica_id].downstream
+ | ---
+ | ...
+d ~= nil and d.system_message ~= nil and d.message ~= nil or i
+ | ---
+ | - true
+ | ...
+
+box.schema.user.revoke('guest', 'replication')
+ | ---
+ | ...

test/replication/gh-4402-info-errno.test.lua

+test_run = require('test_run').new()
+
+--
+-- gh-4402: replication info table should contain not only
+-- Tarantool's error, but also a system error (errno's message)
+-- when possible.
+--
+
+box.schema.user.grant('guest', 'replication')
+
+test_run:cmd('create server replica with rpl_master=default, script="replication/replica.lua"')
+test_run:cmd('start server replica')
+i = box.info
+replica_id = i.id % 2 + 1
+d = i.replication[replica_id].downstream
+d ~= nil and d.status == 'follow' or i
+
+test_run:cmd('stop server replica')
+test_run:cmd("cleanup server replica")
+test_run:cmd("delete server replica")
+i = box.info
+d = i.replication[replica_id].downstream
+d ~= nil and d.system_message ~= nil and d.message ~= nil or i
+
+box.schema.user.revoke('guest', 'replication')

test/replication/suite.cfg

@@ -11,6 +11,7 @@
     "on_schema_init.test.lua": {},
     "long_row_timeout.test.lua": {},
     "join_without_snap.test.lua": {},
+    "gh-4402-info-errno.test.lua": {},
     "gh-4606-admin-creds.test.lua": {},
     "*": {
         "memtx": {"engine": "memtx"},