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Cookbook recipes

Cookbook recipes

Here are contributions of Lua programs for some frequent or tricky situations.

You can execute any of these programs by copying the code into a .lua file, and then entering chmod +x ./program-name.lua and ./program-name.lua on the terminal.

The first line is a “hashbang”:

#!/usr/bin/env tarantool

This runs Tarantool Lua application server, which should be on the execution path.

Use freely.

hello_world.lua

The standard example of a simple program.

#!/usr/bin/env tarantool

print('Hello, World!')

console_start.lua

Use box.once() to initialize a database (creating spaces) if this is the first time the server has been run. Then use console.start() to start interactive mode.

#!/usr/bin/env tarantool

-- Configure database
box.cfg {
    listen = 3313
}

box.once("bootstrap", function()
    box.schema.space.create('tweedledum')
    box.space.tweedledum:create_index('primary',
        { type = 'TREE', parts = {1, 'unsigned'}})
end)

require('console').start()

fio_read.lua

Use the fio module to open, read, and close a file.

#!/usr/bin/env tarantool

local fio = require('fio')
local errno = require('errno')
local f = fio.open('/tmp/xxxx.txt', {'O_RDONLY' })
if not f then
    error("Failed to open file: "..errno.strerror())
end
local data = f:read(4096)
f:close()
print(data)

fio_write.lua

Use the fio module to open, write, and close a file.

#!/usr/bin/env tarantool

local fio = require('fio')
local errno = require('errno')
local f = fio.open('/tmp/xxxx.txt', {'O_CREAT', 'O_WRONLY', 'O_APPEND'},
    tonumber('0666', 8))
if not f then
    error("Failed to open file: "..errno.strerror())
end
f:write("Hello\n");
f:close()

ffi_printf.lua

Use the LuaJIT ffi library to call a C built-in function: printf(). (For help understanding ffi, see the FFI tutorial.)

#!/usr/bin/env tarantool

local ffi = require('ffi')
ffi.cdef[[
    int printf(const char *format, ...);
]]

ffi.C.printf("Hello, %s\n", os.getenv("USER"));

ffi_gettimeofday.lua

Use the LuaJIT ffi library to call a C function: gettimeofday(). This delivers time with millisecond precision, unlike the time function in Tarantool’s clock module.

#!/usr/bin/env tarantool

local ffi = require('ffi')
ffi.cdef[[
    typedef long time_t;
    typedef struct timeval {
    time_t tv_sec;
    time_t tv_usec;
} timeval;
    int gettimeofday(struct timeval *t, void *tzp);
]]

local timeval_buf = ffi.new("timeval")
local now = function()
    ffi.C.gettimeofday(timeval_buf, nil)
    return tonumber(timeval_buf.tv_sec * 1000 + (timeval_buf.tv_usec / 1000))
end

ffi_zlib.lua

Use the LuaJIT ffi library to call a C library function. (For help understanding ffi, see the FFI tutorial.)

#!/usr/bin/env tarantool

local ffi = require("ffi")
ffi.cdef[[
    unsigned long compressBound(unsigned long sourceLen);
    int compress2(uint8_t *dest, unsigned long *destLen,
    const uint8_t *source, unsigned long sourceLen, int level);
    int uncompress(uint8_t *dest, unsigned long *destLen,
    const uint8_t *source, unsigned long sourceLen);
]]
local zlib = ffi.load(ffi.os == "Windows" and "zlib1" or "z")

-- Lua wrapper for compress2()
local function compress(txt)
    local n = zlib.compressBound(#txt)
    local buf = ffi.new("uint8_t[?]", n)
    local buflen = ffi.new("unsigned long[1]", n)
    local res = zlib.compress2(buf, buflen, txt, #txt, 9)
    assert(res == 0)
    return ffi.string(buf, buflen[0])
end

-- Lua wrapper for uncompress
local function uncompress(comp, n)
    local buf = ffi.new("uint8_t[?]", n)
    local buflen = ffi.new("unsigned long[1]", n)
    local res = zlib.uncompress(buf, buflen, comp, #comp)
    assert(res == 0)
    return ffi.string(buf, buflen[0])
end

-- Simple test code.
local txt = string.rep("abcd", 1000)
print("Uncompressed size: ", #txt)
local c = compress(txt)
print("Compressed size: ", #c)
local txt2 = uncompress(c, #txt)
assert(txt2 == txt)

ffi_meta.lua

Use the LuaJIT ffi library to access a C object via a metamethod (a method which is defined with a metatable).

#!/usr/bin/env tarantool

local ffi = require("ffi")
ffi.cdef[[
typedef struct { double x, y; } point_t;
]]

local point
local mt = {
  __add = function(a, b) return point(a.x+b.x, a.y+b.y) end,
  __len = function(a) return math.sqrt(a.x*a.x + a.y*a.y) end,
  __index = {
    area = function(a) return a.x*a.x + a.y*a.y end,
  },
}
point = ffi.metatype("point_t", mt)

local a = point(3, 4)
print(a.x, a.y)  --> 3  4
print(#a)        --> 5
print(a:area())  --> 25
local b = a + point(0.5, 8)
print(#b)        --> 12.5

count_array.lua

Use the ‘#’ operator to get the number of items in an array-like Lua table. This operation has O(log(N)) complexity.

#!/usr/bin/env tarantool

array = { 1, 2, 3}
print(#array)

count_array_with_nils.lua

Missing elements in arrays, which Lua treats as “nil”s, cause the simple “#” operator to deliver improper results. The “print(#t)” instruction will print “4”; the “print(counter)” instruction will print “3”; the “print(max)” instruction will print “10”. Other table functions, such as table.sort(), will also misbehave when “nils” are present.

#!/usr/bin/env tarantool

local t = {}
t[1] = 1
t[4] = 4
t[10] = 10
print(#t)
local counter = 0
for k,v in pairs(t) do counter = counter + 1 end
print(counter)
local max = 0
for k,v in pairs(t) do if k > max then max = k end end
print(max)

count_array_with_nulls.lua

Use explicit NULL values to avoid the problems caused by Lua’s nil == missing value behavior. Although json.NULL == nil is true, all the print instructions in this program will print the correct value: 10.

#!/usr/bin/env tarantool

local json = require('json')
local t = {}
t[1] = 1; t[2] = json.NULL; t[3]= json.NULL;
t[4] = 4; t[5] = json.NULL; t[6]= json.NULL;
t[6] = 4; t[7] = json.NULL; t[8]= json.NULL;
t[9] = json.NULL
t[10] = 10
print(#t)
local counter = 0
for k,v in pairs(t) do counter = counter + 1 end
print(counter)
local max = 0
for k,v in pairs(t) do if k > max then max = k end end
print(max)

count_map.lua

Get the number of elements in a map-like table.

#!/usr/bin/env tarantool

local map = { a = 10, b = 15, c = 20 }
local size = 0
for _ in pairs(map) do size = size + 1; end
print(size)

swap.lua

Use a Lua peculiarity to swap two variables without needing a third variable.

#!/usr/bin/env tarantool

local x = 1
local y = 2
x, y = y, x
print(x, y)

class.lua

Create a class, create a metatable for the class, create an instance of the class. Another illustration is at http://lua-users.org/wiki/LuaClassesWithMetatable.

#!/usr/bin/env tarantool

-- define class objects
local myclass_somemethod = function(self)
    print('test 1', self.data)
end

local myclass_someothermethod = function(self)
    print('test 2', self.data)
end

local myclass_tostring = function(self)
    return 'MyClass <'..self.data..'>'
end

local myclass_mt = {
    __tostring = myclass_tostring;
    __index = {
        somemethod = myclass_somemethod;
        someothermethod = myclass_someothermethod;
    }
}

-- create a new object of myclass
local object = setmetatable({ data = 'data'}, myclass_mt)
print(object:somemethod())
print(object.data)

garbage.lua

Force Lua garbage collection with the collectgarbage function.

#!/usr/bin/env tarantool

collectgarbage('collect')

fiber_producer_and_consumer.lua

Start one fiber for producer and one fiber for consumer. Use fiber.channel() to exchange data and synchronize. One can tweak the channel size (ch_size in the program code) to control the number of simultaneous tasks waiting for processing.

#!/usr/bin/env tarantool

local fiber = require('fiber')
local function consumer_loop(ch, i)
    -- initialize consumer synchronously or raise an error()
    fiber.sleep(0) -- allow fiber.create() to continue
    while true do
        local data = ch:get()
        if data == nil then
            break
        end
        print('consumed', i, data)
        fiber.sleep(math.random()) -- simulate some work
    end
end

local function producer_loop(ch, i)
    -- initialize consumer synchronously or raise an error()
    fiber.sleep(0) -- allow fiber.create() to continue
    while true do
        local data = math.random()
        ch:put(data)
        print('produced', i, data)
    end
end

local function start()
    local consumer_n = 5
    local producer_n = 3

    -- Create a channel
    local ch_size = math.max(consumer_n, producer_n)
    local ch = fiber.channel(ch_size)

    -- Start consumers
    for i=1, consumer_n,1 do
        fiber.create(consumer_loop, ch, i)
    end

    -- Start producers
    for i=1, producer_n,1 do
        fiber.create(producer_loop, ch, i)
    end
end

start()
print('started')

socket_tcpconnect.lua

Use socket.tcp_connect() to connect to a remote host via TCP. Display the connection details and the result of a GET request.

#!/usr/bin/env tarantool

local s = require('socket').tcp_connect('google.com', 80)
print(s:peer().host)
print(s:peer().family)
print(s:peer().type)
print(s:peer().protocol)
print(s:peer().port)
print(s:write("GET / HTTP/1.0\r\n\r\n"))
print(s:read('\r\n'))
print(s:read('\r\n'))

socket_tcp_echo.lua

Use socket.tcp_connect() to set up a simple TCP server, by creating a function that handles requests and echos them, and passing the function to socket.tcp_server(). This program has been used to test with 100,000 clients, with each client getting a separate fiber.

#!/usr/bin/env tarantool

local function handler(s, peer)
    s:write("Welcome to test server, " .. peer.host .."\n")
    while true do
        local line = s:read('\n')
        if line == nil then
            break -- error or eof
        end
        if not s:write("pong: "..line) then
            break -- error or eof
        end
    end
end

local server, addr = require('socket').tcp_server('localhost', 3311, handler)

getaddrinfo.lua

Use socket.getaddrinfo() to perform non-blocking DNS resolution, getting both the AF_INET6 and AF_INET information for ‘google.com’. This technique is not always necessary for tcp connections because socket.tcp_connect() performs socket.getaddrinfo under the hood, before trying to connect to the first available address.

#!/usr/bin/env tarantool

local s = require('socket').getaddrinfo('google.com', 'http', { type = 'SOCK_STREAM' })
print('host=',s[1].host)
print('family=',s[1].family)
print('type=',s[1].type)
print('protocol=',s[1].protocol)
print('port=',s[1].port)
print('host=',s[2].host)
print('family=',s[2].family)
print('type=',s[2].type)
print('protocol=',s[2].protocol)
print('port=',s[2].port)

socket_udp_echo.lua

Tarantool does not currently have a udp_server function, therefore socket_udp_echo.lua is more complicated than socket_tcp_echo.lua. It can be implemented with sockets and fibers.

#!/usr/bin/env tarantool

local socket = require('socket')
local errno = require('errno')
local fiber = require('fiber')

local function udp_server_loop(s, handler)
    fiber.name("udp_server")
    while true do
        -- try to read a datagram first
        local msg, peer = s:recvfrom()
        if msg == "" then
            -- socket was closed via s:close()
            break
        elseif msg ~= nil then
            -- got a new datagram
            handler(s, peer, msg)
        else
            if s:errno() == errno.EAGAIN or s:errno() == errno.EINTR then
                -- socket is not ready
                s:readable() -- yield, epoll will wake us when new data arrives
            else
                -- socket error
                local msg = s:error()
                s:close() -- save resources and don't wait GC
                error("Socket error: " .. msg)
            end
        end
    end
end

local function udp_server(host, port, handler)
    local s = socket('AF_INET', 'SOCK_DGRAM', 0)
    if not s then
        return nil -- check errno:strerror()
    end
    if not s:bind(host, port) then
        local e = s:errno() -- save errno
        s:close()
        errno(e) -- restore errno
        return nil -- check errno:strerror()
    end

    fiber.create(udp_server_loop, s, handler) -- start a new background fiber
    return s
end

A function for a client that connects to this server could look something like this …

local function handler(s, peer, msg)
    -- You don't have to wait until socket is ready to send UDP
    -- s:writable()
    s:sendto(peer.host, peer.port, "Pong: " .. msg)
end

local server = udp_server('127.0.0.1', 3548, handler)
if not server then
    error('Failed to bind: ' .. errno.strerror())
end

print('Started')

require('console').start()

http_get.lua

Use the http module to get data via HTTP.

#!/usr/bin/env tarantool

local http_client = require('http.client')
local json = require('json')
local r = http_client.get('http://api.openweathermap.org/data/2.5/weather?q=Oakland,us')
if r.status ~= 200 then
    print('Failed to get weather forecast ', r.reason)
    return
end
local data = json.decode(r.body)
print('Oakland wind speed: ', data.wind.speed)

http_send.lua

Use the http module to send data via HTTP.

#!/usr/bin/env tarantool

local http_client = require('http.client')
local json = require('json')
local data = json.encode({ Key = 'Value'})
local headers = { Token = 'xxxx', ['X-Secret-Value'] = 42 }
local r = http_client.post('http://localhost:8081', data, { headers = headers})
if r.status == 200 then
    print 'Success'
end

http_server.lua

Use the http rock (which must first be installed) to turn Tarantool into a web server.

#!/usr/bin/env tarantool

local function handler(self)
    return self:render{ json = { ['Your-IP-Is'] = self.peer.host } }
end

local server = require('http.server').new(nil, 8080) -- listen *:8080
server:route({ path = '/' }, handler)
server:start()
-- connect to localhost:8080 and see json

http_generate_html.lua

Use the http rock (which must first be installed) to generate HTML pages from templates. The http rock has a fairly simple template engine which allows execution of regular Lua code inside text blocks (like PHP). Therefore there is no need to learn new languages in order to write templates.

#!/usr/bin/env tarantool

local function handler(self)
local fruits = { 'Apple', 'Orange', 'Grapefruit', 'Banana'}
    return self:render{ fruits = fruits }
end

local server = require('http.server').new(nil, 8080) -- nil means '*'
server:route({ path = '/', file = 'index.html.lua' }, handler)
server:start()

An “HTML” file for this server, including Lua, could look like this (it would produce “1 Apple | 2 Orange | 3 Grapefruit | 4 Banana”).

<html>
<body>
    <table border="1">
        % for i,v in pairs(fruits) do
        <tr>
            <td><%= i %></td>
            <td><%= v %></td>
        </tr>
        % end
    </table>
</body>
</html>