Add example implementation for lua connector.

tests/examples/lua/README.md

+# TDengine driver connector for Lua
+
+It's a lua implementation for [TDengine](https://github.com/taosdata/TDengine), an open-sourced big data platform designed and optimized for the Internet of Things (IoT), Connected Cars, Industrial IoT, and IT Infrastructure and Application Monitoring. You may needs install Lua5.3 .
+
+## Dependencies
+- Lua: 
+```
+https://www.lua.org/
+```
+
+## Run with Sample
+
+Build driver lib:
+```
+./build.sh
+```
+Run lua sample:
+```
+lua test.lua
+```

tests/examples/lua/build.sh

+gcc lua_connector.c -fPIC -shared -o luaconnector.so -Wall -ltaos
+

tests/examples/lua/lua_connector.c

+#include <stdio.h>
+#include <math.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <lua.h>
+#include <lauxlib.h>
+#include <lualib.h>
+#include <taos.h>
+
+static int l_connect(lua_State *L)
+{
+  TAOS *    taos;
+  char *host = lua_tostring(L, 1);
+  char *user = lua_tostring(L, 2);
+  char *password = lua_tostring(L, 3);
+  char *database = lua_tostring(L, 4);
+  int port =luaL_checknumber(L, 5);
+  taos_init();
+  
+  lua_newtable(L);
+  int table_index = lua_gettop(L);
+
+  taos = taos_connect(host, user,password,database, port);
+  if (taos == NULL) {
+    printf("failed to connect to server, reason:%s\n", taos_errstr(taos));
+    
+    lua_pushnumber(L, -1);
+    lua_setfield(L, table_index, "code");
+    lua_pushstring(L, taos_errstr(taos));
+    lua_setfield(L, table_index, "error");    
+    lua_pushlightuserdata(L,NULL);
+  }else{
+    printf("success to connect to server\n");
+    lua_pushnumber(L, 0);
+    lua_setfield(L, table_index, "code");
+    lua_pushstring(L, taos_errstr(taos));
+    lua_setfield(L, table_index, "error");    
+    lua_pushlightuserdata(L,taos);
+    lua_setfield(L, table_index, "conn");
+  }
+
+  return 1;
+}
+
+static int l_query(lua_State *L){
+  TAOS *    taos= lua_topointer(L,1);
+  char *s = lua_tostring(L, 2);
+  TAOS_RES *result;
+  lua_newtable(L);
+  int table_index = lua_gettop(L);
+
+  printf("receive command:%s\r\n",s);
+  if(taos_query(taos, s)!=0){
+    printf("failed, reason:%s\n", taos_errstr(taos));
+    lua_pushnumber(L, -1);
+    lua_setfield(L, table_index, "code");    
+    lua_pushstring(L, taos_errstr(taos));
+    lua_setfield(L, table_index, "error");    
+   
+    return 1;
+    
+  }else{
+    result = taos_use_result(taos);
+
+    if (result == NULL) {
+      printf("failed to get result, reason:%s\n", taos_errstr(taos));
+      lua_pushnumber(L, -2);
+      lua_setfield(L, table_index, "code");    
+      lua_pushstring(L, taos_errstr(taos));
+      lua_setfield(L, table_index, "error");    
+      return 1;
+    }
+
+    TAOS_ROW    row;
+    int         rows = 0;
+    int         num_fields = taos_field_count(taos);
+    TAOS_FIELD *fields = taos_fetch_fields(result);
+    char        temp[256];
+
+    lua_pushnumber(L, 0);
+    lua_setfield(L, table_index, "code");
+    lua_newtable(L);
+    
+    while ((row = taos_fetch_row(result))) {
+      rows++;
+      taos_print_row(temp, row, fields, num_fields);
+      printf("%s\n", temp);
+      lua_pushnumber(L,rows);
+      lua_pushstring(L,temp);
+      lua_settable(L,-3);
+    }
+    
+    taos_free_result(result);    
+  }
+  
+  lua_setfield(L, table_index, "item");
+  return 1;
+}
+
+static int l_close(lua_State *L){
+  TAOS *    taos= lua_topointer(L,1);
+  lua_newtable(L);
+  int table_index = lua_gettop(L);
+  
+  if(taos == NULL){
+    lua_pushnumber(L, -1);
+    lua_setfield(L, table_index, "code");    
+    lua_pushstring(L, "null pointer.");
+    lua_setfield(L, table_index, "error"); 
+  }else{
+    taos_close(taos);   
+    lua_pushnumber(L, 0);
+    lua_setfield(L, table_index, "code");    
+    lua_pushstring(L, "done.");
+    lua_setfield(L, table_index, "error");    
+  }
+  return 1;
+}
+
+static const struct luaL_Reg lib[] = {
+    {"connect", l_connect},
+    {"query", l_query},
+    {"close", l_close},
+    {NULL, NULL}
+};
+
+extern int luaopen_luaconnector(lua_State* L)
+{
+    luaL_newlib(L, lib);
+
+    return 1;
+}

tests/examples/lua/test.lua

+local mylib = require "luaconnector"
+
+local host="127.0.0.1"
+local user="root"
+local password="taosdata"
+local db =nil
+local port=6030
+local conn
+
+local res = mylib.connect(host,user,password,db,port)
+if res.code ~=0 then
+   print(res.error)
+   return
+else
+   conn = res.conn
+end
+
+local res = mylib.query(conn,"drop database demo")
+
+res = mylib.query(conn,"create database demo")
+if res.code ~=0 then
+   print(res.error)
+   return
+end
+
+res = mylib.query(conn,"use demo")
+if res.code ~=0 then
+   print(res.error)
+   return
+end
+
+res = mylib.query(conn,"create table m1 (ts timestamp, speed int)")
+if res.code ~=0 then
+   print(res.error)
+   return
+end
+
+res = mylib.query(conn,"insert into m1 values (1592222222223,3)")
+
+res = mylib.query(conn,"select * from m1")
+
+if res.code ==0 then
+   print("in lua, result:")
+   for i=1,#(res.item) do
+      print(res.item[i])
+   end
+end