07 January 2013

How I created a minimalistic blog platform with lua

My motivation was just having a simple no frills blog for publishing some of my latest writings. I have also worked a bit with Wordpress lately, and I wanted to play with a comepletely different software stack. This project is not very serious and is meant for personal use. The most unusual part about this project is it's usage of nginx as the "app server". This is possible using lua, since there is a nginx lua module that enables you to call lua from the nginx conf. Have a look at openresty's site for more about what it enables you to do.

Let me begin by listing the components being used:


Now we know the components in use, so now I can explain how they work togheter. Lua runs inside nginx and is being used as backend as it is being called in the web developer world. There is little to no javascript running in this setup. The backend loads a few templates (header, footer, etc) using Zed Shaw's tiny templating engine from another micro framework in Lua, check it out here: Tir Microframework

The index template looks in the predefined git repository for a list for markdown files, these will be the blog posts, then it runs git log to figure out the date the blog post was created and displays a list.

The blog post template extracts a filename from the URL and loads the corresponding Markdown file. The markdown gets compiled with Niklas Frykholm's Markdown parser written in lua.

Each view has a simple counter in redis, with the primary motivation of showcasing the speed of these pages. The Redis database is not really needed for any functionality.

Publishing a new article is then just the small matter of writing a Markdown file and pushing it to the blog repository and then it will display in the list and have its own permanent URL.

Show me some code!

index.lua (with some parts edited out for clarity)

-- load our template engine
local tirtemplate = require('tirtemplate')
-- Load redis
local redis = require "resty.redis"
local markdown = require "markdown"

-- Set the content type
ngx.header.content_type = 'text/html';

-- use nginx $root variable for template dir, needs trailing slash
TEMPLATEDIR = ngx.var.root .. 'luanew/';
-- The git repository storing the markdown files. Needs trailing slash
BLAGTITLE = 'hveem.no'

-- the db global
red = nil

-- Get all the files in a dir
local function get_posts()
    local directory = shell_escape(BLAGDIR)
    local i, t, popen = 0, {}, io.popen
    local handle = popen('ls "'..directory..'"')
    if not handle then return {} end
    for filename in handle:lines() do
        i = i + 1
        t[i] = filename
    return t

-- Find the commit dates for  a file in a git dir was
local function file2gitci(dir, filename)
    local i, t, popen = 0, {}, io.popen
    local dir, filename = shell_escape(dir), shell_escape(filename)
    local cmd = 'git --git-dir "'..dir..'.git" log --pretty=format:"%ct" --date=local --reverse -- "'..filename..'"'
    local handle = popen(cmd)
    for gitdate in handle:lines() do
        i = i + 1
        t[i] = gitdate
    return t

local function filename2title(filename)
    title = filename:gsub('.md$', ''):gsub('-', ' ')
    return title

function slugify(title)
    slug = title:gsub(' ', '-')
    return slug

--- Better safe than sorry
function shell_escape(s)
    return (tostring(s) or ''):gsub('"', '\\"')

-- Index view
local function index()

    -- increment index counter
    local counter, err = red:incr("index_visist_counter")

    local postlist = get_posts()
    local posts = {}
    for i, post in pairs(postlist) do
        local gitdate = file2gitci(BLAGDIR, post)
        -- Skip unversioned files
        if #gitdate > 0 then 
            -- Use first date
            posts[gitdate[1]] = filename2title(post)
    -- Sort on timestamp key
    table.sort(posts, function(a,b) return tonumber(a)>tonumber(b) end)

    -- load template
    local page = tirtemplate.tload('index.html')
    local context = {
        title = BLAGTITLE, 
        counter = tostring(counter),
        posts = posts,
    -- render template with counter as context
    -- and return it to nginx
    ngx.print( page(context) )

-- blog view for a single post
local function blog(match)
    local page = match[1] 
    local mdfiles = get_posts()
    local mdcurrent = nil
    for i, mdfile in pairs(mdfiles) do
        if page..'.md' == mdfile then
            mdcurrent = mdfile
    -- No match, return 404
    if not mdcurrent then
        return ngx.HTTP_NOT_FOUND

    local mdfile =  BLAGDIR .. mdcurrent
    local mdfilefp = assert(io.open(mdfile, 'r'))
    local mdcontent = mdfilefp:read('*a')
    local mdhtml = markdown(mdcontent) 
    local gitdate = file2gitci(BLAGDIR, mdcurrent)
    -- increment visist counter
    local counter, err = red:incr(page..":visit")

    local ctx = {
        created = ngx.http_time(gitdate[1]),
        content = mdhtml,
        counter = counter,
    local template = tirtemplate.tload('blog.html')
    ngx.print( template(ctx) )


-- Initialise db
local function init_db()
    -- Start redis connection
    red = redis:new()
    local ok, err = red:connect("unix:/var/run/redis/redis.sock")
    if not ok then
        ngx.say("failed to connect: ", err)

-- End db, we could close here, but park it in the pool instead
local function end_db()
    -- put it into the connection pool of size 100,
    -- with 0 idle timeout
    local ok, err = red:set_keepalive(0, 100)
    if not ok then
        ngx.say("failed to set keepalive: ", err)

-- mapping patterns to views
local routes = {
    ['$']         = index,
    ['(.*)$']     = blog,

local BASE = '/'
-- iterate route patterns and find view
for pattern, view in pairs(routes) do
    local uri = '^' .. BASE .. pattern
    local match = ngx.re.match(ngx.var.uri, uri, "") -- regex mather in compile mode
    if match then
        exit = view(match) or ngx.HTTP_OK
        ngx.exit( exit )
-- no match, return 404
ngx.exit( ngx.HTTP_NOT_FOUND )

nginx.conf, the Nginx web server configuration

lua_package_path '/home/www/lua/?.lua;;';
server {
  listen 80;
  server_name example.no www.example.no;
  set $root /home/www/;
  root $root;

  # Serve static if file exist, or send to lua
  location / { try_files $uri @lua; }
  # Lua app
  location @lua {
      content_by_lua_file $root/lua/index.lua;

Read the followup, where I change the backend a bit to use redis.


You can find the source at my github repository for this project.

Also read