Lua scripting basics and cases

The article is organized in bilibili Dark horse programmer’s video tutorial

Lua is introduced

What is Lua?

The characteristics of the lua

• Support for procedure-oriented programming and functional programming;
• Automatic memory management; Only provides a general type of table (table), with it can achieve array, hash table, collection, object;
• Language built-in pattern matching; Closure (closure); A function can also be viewed as a value; Multithreading (collaborative processes, not threads supported by the operating system) support;
• Closures and tables make it easy to support some of the key mechanisms needed for object-oriented programming, such as data abstraction, virtual functions, inheritance, and overloading.

Application scenarios of Lua

The installation of the lua

There e are Linux and MAC versions installed. We use the Linux version of the installation, first we prepare a Linux virtual machine.

To install, run the following command on Linux.

Curl the -r -o http://www.lua.org/ftp/lua-5.3.5.tar.gz tar ZXF lua - 5.3.5. Tar. GzcdLua - 5.3.5 make Linuxtest
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Note: The following errors may occur during installation:To install lua dependent libraries, run the following command:

yum install libtermcap-devel ncurses-devel libevent-devel readline-devel
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Then run the Lua test to check whether Lua is successfully installed

[root@localhost ~]# luaCopyright (C) 1994-2008 Lua.org, PUC-RioCopy the code

Entry procedures

vi hello.lua
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print("hello");
print("hello lua!");
print("hello world!");
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lua hello.lua
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hello
hello lua!
hello world!
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Basic syntax of LUA

Lua has interactive programming and scripted programming. Interactive programming is simply typing in the syntax and executing it. Scripting requires writing scripts and then executing commands to execute the scripts. Scripting is generally used. (For example, create a hello.lua file, enter the contents of the file, and execute lua hell.lua)

(1) Interactive programming

Lua provides an interactive programming mode. We can type programs on the command line and see the results immediately.

Lua interactive programming mode can be enabled with the command Lua -i or Lua:

lua -i
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The diagram below:

(2) Scripted programming

We can save Lua program code to a lua-ending file and execute it. This pattern is called scripted programming, such as writing Lua syntax to a hello. Lua file in the introductory program.

annotation

--
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--[[multiline comment --]]
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Define variables

Global variables. By default, defining a variable is a global variable,

To use a local variable, declare it local. For example:

-- Global variable assignment
a=1
-- Local variable assignment
local b=2 
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If the variable is not initialized: its value is nil which is different from null in Java.

As shown below:

Data types in Lua

print(type("Hello world"))      --> string
print(type(10.4*3))             --> number
print(type(print))              --> function
print(type(type))               --> function
print(type(true))               --> boolean
print(type(nil))                --> nil
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Process control

(1) if statements

A Lua if statement consists of a Boolean expression as a condition, followed by other statements.

Grammar:

if(Boolean expression)then
   --[statement executed when Boolean expression is true --]
end
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Example:

(2) the if… Else statements

Lua if statements can be paired with else statements to execute an else statement block if the if conditional expression is false.

Grammar:

if(Boolean expression)then
   --[execute block when Boolean expression is true --]
else
   --[execute block when Boolean expression is false --]
end
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Example:

cycle

while(condition)
do
   statements
end
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a=10
while( a < 20 )
do
   print("The value of a is:, a)
   a = a+1
end
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for var=exp1,exp2,exp3 
do< executor >end  
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for i=1.9.2
do
   print(i)
end
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repeat
   statements
until( condition )
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function

Functions can also be defined in Lua, similar to methods in Java. Such as:

--[[function returns the maximum value of two values --]]
function max(num1, num2)

   if (num1 > num2) then
      result = num1;
   else
      result = num2;
   end

   return result; 
end
Call function
print("The maximum value between the two values is.max(10.4))
print("The maximum value between the two values is.max(5.6))
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Results after execution:

The maximum value of the comparison is 10 and the maximum value of the comparison is 6Copy the code

… : indicates splicing

table

Initialize the table
mytable = {}

- the specified value
mytable[1] ="Lua"

-- Remove reference
mytable = nil
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The module

(1) Module definition

Modules are similar to an encapsulation library. Starting from Lua 5.1, Lua has added a standard module management mechanism, which can put some common code in a file and call it in the form of API interface in other places, which is beneficial to code reuse and reduce code coupling.

Create a file called module.lua and create a separate module in module.lua with the following code:

-- The file name is module.lua
-- Define a module named module
module = {}
 
Define a constant
module.constant = "This is a constant."
 
Define a function
function module.func1(a)
    print("This is a public function")
end
 
local function func2(a)
    print("This is a private function!")
end
 
function module.func3(a)
    func2()
end
 
return module
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The structure of a module is the structure of a table, so you can operate on constants or functions in the module as if you were calling elements in the table.

Func2 above is declared as a local variable of the block, representing a private function. Therefore, the private function in the module cannot be accessed externally and must be called through the public function in the module.

(2) the require function

Require is used to introduce other modules, similar to Java classes that reference other classes.

Usage:

require("< module name >")
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require "< module name >"
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Either way.

We can import the module defined above and create a test_module.lua file as follows:

-- test_module. Lua files
-- module is the module mentioned above in module.lua
require("module")

print(module.constant)

module.func3()
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OpenResty introduction

Install openresty

Linux installation openresty:

1. Add the warehouse and run the command

 yum install yum-utils
 yum-config-manager --add-repo https://openresty.org/package/centos/openresty.repo
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2. Perform the installation

yum install openresty
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3. After the installation, the default directory is as follows:

/usr/local/openresty
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Install nginx

cd /usr/local/openresty/nginx/conf
vi nginx.conf
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Test access

Restart the centos VIRTUAL machine and access the test Nginx

Visit address:http://server IP address /

Lua script instance: page AD cache loading and reading

Demand analysis

Need to display advertising information on the page.

Lua + Nginx configuration

Request: /update_content Parameter: id -- Specifies the ID of the AD category. Returned value: JSONCopy the code

ngx.header.content_type="application/json; charset=utf8"
local cjson = require("cjson")
local mysql = require("resty.mysql")
local uri_args = ngx.req.get_uri_args()
local id = uri_args["id"]

local db = mysql:new()
db:set_timeout(1000)
local props = {
    host = "8.131.64.45",
    port = 3306,
    database = "changgou_content",
    user = "root",
    password = "[email protected]"
}

local res = db:connect(props)
local select_sql = "select url,pic from tb_content where status ='1' and category_id="..id.." order by sort_order"
res = db:query(select_sql)
db:close(a)local redis = require("resty.redis")
local red = redis:new()
red:set_timeout(2000)

local ip ="8.131.66.136"
local port = 6379
red:connect(ip,port)
red:auth("csp19990129")
red:select(0)
red:set("content_"..id,cjson.encode(res))
red:close()

ngx.say("{flag:true}")
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Modify the/usr/local/openresty/nginx/conf/nginx.confFile: Add header information and location information:

The code is as follows:

server {
    listen       80; server_name localhost; User request /update_content? id=1Location /update_content {content_by_lua_file /root/lua/update_content.lua; }}Copy the code

Define the lua cache namespace, modify nginx.conf, add the following code:



The code is as follows:

# lua cache namespace lua_shared_dict dis_cache128m; 
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Browser test execution cache:

http://server IP/update_Content? Id =1

Go to the Redis client to test whether the cache is successful:



As shown, the data is obtained and the cache is successful!

(2) Implementation idea – obtain data from Redis

Implementation idea:

Define a request where the user gets a list of ads based on the ID of the AD category. Get the data directly from Redis using lua scripts.

Define the request:

Request :/read_content Parameter: id Returned value: JSONCopy the code

Create read_content.lua in /root/lua:

-- Sets the response header type
ngx.header.content_type="application/json; charset=utf8"
Gets the ID of the parameter in the request
local uri_args = ngx.req.get_uri_args();
local id = uri_args["id"];
-- Introducing the Redis library
local redis = require("resty.redis");
Create a Redis object
local red = redis:new()
-- Set the timeout period
red:set_timeout(2000)
- the connection
local ok, err = red:connect("Server IP".6379)
Get the value of key
local rescontent=red:get("content_"..id)
Output to the return response
ngx.say(rescontent)
-- Close the connection
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in/usr/local/openresty/nginx/conf/nginx.confThe configuration is as follows:

As shown in figure:

Code:

User request /read_content? id=1Location /read_content {content_by_lua_file /root/lua/read_content.lua; }Copy the code

(3) Join openResty local cache

There is no problem in the above way, but if all the requests go to Redis, redis will be under great pressure, so we generally adopt multi-level caching to reduce the service pressure of the downstream system. Refer to the implementation of the basic idea diagram.

• Query the OpenResty local cache first if not
• Query data in Redis, if no
• Mysql > select * from ‘mysql’;

Modify the read_content.lua file as follows:

The complete configuration is as follows:

ngx.header.content_type="application/json; charset=utf8"
local uri_args = ngx.req.get_uri_args();
local id = uri_args["id"];
Get the local cache
local cache_ngx = ngx.shared.dis_cache;
Get local cache data based on ID
local contentCache = cache_ngx:get('content_cache_'..id);

if contentCache == "" or contentCache == nil then
    local redis = require("resty.redis");
    local red = redis:new()
    red:set_timeout(2000)
    red:connect("8.xxx.xx.xx6".6379)
    -- Password and selected bucket
    red:auth("csxxxxx29")
    red:select(0)

    local rescontent=red:get("content_"..id);

    if ngx.null == rescontent then
        local cjson = require("cjson");
        local mysql = require("resty.mysql");
        local db = mysql:new();
        db:set_timeout(2000)
        local props = {
            host = "8.xxx.xx.x5",
            port = 3306,
            database = "changgou_content",
            user = "root",
            password = "CSPxxxxxx.com"
        }
        local res = db:connect(props);
        local select_sql = "select url,pic from tb_content where status ='1' and category_id="..id.." order by sort_order";
        res = db:query(select_sql);
        local responsejson = cjson.encode(res);
        red:set("content_"..id,responsejson);
        ngx.say(responsejson);
        db:close(a)else
        cache_ngx:set('content_cache_'..id, rescontent, 10*60);
        ngx.say(rescontent)
    end
    red:close(a)else
    ngx.say(contentCache)
end
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The test address: http://192.168.211.132/update_content? id=1

All ads with category ID=1 will be queried and stored in Redis cache:



Test address:http://server IP/update_Content? Id =1

All ads with category ID=1 will be obtained: