The Boston Diaries

The ongoing saga of a programmer who doesn't live in Boston, nor does he even like Boston, but yet named his weblog/journal “The Boston Diaries.”

Go figure.

Tuesday, April 06, 2010

Write Apache modules quickly in Lua

I really like mod_lua, even in its alpha state. In less than five minutes I had a webpage that would display a different quote each time it was referenced. I was able to modify the Lua based qotd, changing:

QUOTESFILE = "/home/spc/quotes/quotes.txt"
quotes     = {}

do
  local eoln = "\r\n"
  local f    = io.open(QUOTESFILE,"r")
  local s    = ""

  for line in f:lines() do
    if line == "" then
      -- each quote is separated by a blank link
      if #s < 512 then
        table.insert(quotes,s)
      end
      s = ""
    else
      s = s .. line .. eoln
    end
  end

  f:close()
end

math.randomseek(os.time())

function main(socket)
  socket:write(quotes[math.random(#quotes)])
end

to

QUOTESFILE = "/home/spc/quotes/quotes.txt"
quotes     = {}

do
  local eoln = "\r\n"
  local f    = io.open(QUOTESFILE,"r")
  local s    = ""

  for line in f:lines() do
    if line == "" then
      -- each quote is separated by a blank link
      if #s < 512 then
        table.insert(quotes,s)
      end
      s = ""
    else
      s = s .. line .. eoln
    end
  end

  f:close()
end

math.randomseek(os.time())

function handler(r)
  r.content_type = "text/plain"
  r:puts(quotes[math.random(#quotes)])
end

(you can see, it didn't take much), and adding

LuaMapHandler /quote.html /home/spc/web/lua/lib/quote.lua

to the site configuration (what you don't see is the only other line you need, LuaRoot), reload Apache and I now have webpage backed by Lua.

And from there, it isn't much to add some HTML to the output, but it should be clear that adding Apache modules in Lua isn't that hard.

What did take me by surprise is that there's no real way to do the heavy initialization just once. That bit of reading in the quotes file? It's actually done for every request—mod_lua just compiles the code and keeps the compiled version cached and for each request, runs the compiled code. It'd be nice if there was a way to do some persistent initialization once (a feature I use in the current mod_litbook), but as written, mod_lua doesn't have support for that.

I also haven't see any action on my bug report—not a good sign.

I'm wondering if I might not have to pick up the ball mod_lua and run with it …

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