Add the redis.log function in Lua script (#379)

We implement the builtin function `redis.log()` for the Lua script,
but the log level was different between Redis and Kvrocks, so we
choose to keep consistency with Redis's log level to avoid compatible
problem with below mappings(which would make the legacy script happy):

LOG_DEBUG   => NULL
LOG_VERBOSE => INFO
LOG_NOTICE  => INFO
LOG_WARNING => WARNING

LOG_DEBUG would never work since the debug level make no sense in kvrocks

src/scripting.cc

@@ -19,6 +19,13 @@
  * This should be the size of the buffer given to doule to string */
 #define MAX_LONG_DOUBLE_CHARS 5*1024
 
+enum {
+  LL_DEBUG = 0,
+  LL_VERBOSE,
+  LL_NOTICE,
+  LL_WARNING,
+};
+
 extern "C" {
 LUALIB_API int (luaopen_cjson)(lua_State *L);
 LUALIB_API int (luaopen_struct)(lua_State *L);
@@ -53,6 +60,27 @@ namespace Lua {
     lua_pushcfunction(lua, redisPCallCommand);
     lua_settable(lua,  -3);
 
+    /* redis.log and log levels. */
+    lua_pushstring(lua, "log");
+    lua_pushcfunction(lua, redisLogCommand);
+    lua_settable(lua, -3);
+
+    lua_pushstring(lua, "LOG_DEBUG");
+    lua_pushnumber(lua, LL_DEBUG);
+    lua_settable(lua, -3);
+
+    lua_pushstring(lua, "LOG_VERBOSE");
+    lua_pushnumber(lua, LL_VERBOSE);
+    lua_settable(lua, -3);
+
+    lua_pushstring(lua, "LOG_NOTICE");
+    lua_pushnumber(lua, LL_NOTICE);
+    lua_settable(lua, -3);
+
+    lua_pushstring(lua, "LOG_WARNING");
+    lua_pushnumber(lua, LL_WARNING);
+    lua_settable(lua, -3);
+
     /* redis.sha1hex */
     lua_pushstring(lua, "sha1hex");
     lua_pushcfunction(lua, redisSha1hexCommand);
@@ -112,6 +140,54 @@ namespace Lua {
     }
   }
 
+
+  int redisLogCommand(lua_State *lua) {
+    int j, level, argc = lua_gettop(lua);
+
+    if (argc < 2) {
+      lua_pushstring(lua, "redis.log() requires two arguments or more.");
+      return lua_error(lua);
+    }
+    if (!lua_isnumber(lua, -argc)) {
+      lua_pushstring(lua, "First argument must be a number (log level).");
+      return lua_error(lua);
+    }
+    level = lua_tonumber(lua, -argc);
+    if (level < LL_DEBUG || level > LL_WARNING) {
+      lua_pushstring(lua, "Invalid debug level.");
+      return lua_error(lua);
+    }
+    if (level < GetServer()->GetConfig()->loglevel) {
+      return 0;
+    }
+
+    std::string log_message;
+    for (j = 1; j < argc; j++) {
+      size_t len;
+      const char *s;
+      s = lua_tolstring(lua, (-argc)+j, &len);
+      if (s) {
+        if (j != 1)  {
+          log_message += " "+std::string(s, len);
+        } else {
+          log_message = std::string(s, len);
+        }
+      }
+    }
+
+    // The min log level was INFO, DEBUG would never take effect
+    switch (level) {
+      case LL_VERBOSE:  // also regard VERBOSE as INFO here since no VERBOSE level
+      case LL_NOTICE:
+        LOG(INFO) << "[Lua] " << log_message;
+        break;
+      case LL_WARNING:
+        LOG(WARNING) << "[Lua] " << log_message;
+        break;
+    }
+    return 0;
+  }
+
   Status evalGenericCommand(Redis::Connection *conn,
                             const std::vector<std::string> &args,
                             bool evalsha,

src/scripting.h

@@ -29,6 +29,8 @@ int redisSha1hexCommand(lua_State *lua);
 int redisStatusReplyCommand(lua_State *lua);
 int redisErrorReplyCommand(lua_State *lua);
 Status createFunction(Server *srv, const std::string &body, std::string *sha);
+
+int redisLogCommand(lua_State *lua);
 Status evalGenericCommand(Redis::Connection *conn,
                           const std::vector<std::string> &args,
                           bool evalsha,

tests/tcl/tests/unit/scripting.tcl

@@ -352,6 +352,17 @@ start_server {tags {"scripting"}} {
         r sadd myset a b c d e f g h i l m n o p q r s t u v z aa aaa azz
         r eval {return redis.call('smembers',KEYS[1])} 1 myset
     } {a aa aaa azz b c d e f g h i l m n o p q r s t u v z}
+
+    test "Make sure redis.log() works" {
+        set v [r eval { return redis.log(redis.LOG_DEBUG, 'debug level'); } 0]
+        assert_equal "" $v
+        set v [r eval { return redis.log(redis.LOG_VERBOSE, 'verbose level'); } 0]
+        assert_equal "" $v
+        set v [r eval { return redis.log(redis.LOG_NOTICE, 'notice level'); } 0]
+        assert_equal "" $v
+        set v [r eval { return redis.log(redis.LOG_WARNING, 'warning level'); } 0]
+        assert_equal "" $v
+    } {}
 }
 
 start_server {tags {"repl"}} {