Using ErlyWeb templates with MochiWeb

Posted by Dave Bryson on May 05, 2008

Here’s a very simple way to add dynamic templates (views) to a MochiWeb based web front-end. I wouldn’t want to build an entire web application this way, but it’s a quick way to add a simple web interface to your Erlang application.

First I pulled the simple template code from ErlyWeb (erltl.erl) and compiled it with my code.

For this example, here’s a template index.et that shows a list of nodes the Erlang application is connected to.

index.et

<html>
<body>
<h2>Available nodes</h2>
 Total online: <% integer_to_list(length(Data)) %>
 <ul>
   <% [index(A) || A <- Data] %>
</ul>
</body>
</html>

<%@ index(N) %>
<li><% atom_to_list(N) %></li>

Now compile it with “erltl:compile(”index.et)” and put in the same path as your mochiweb app (below).

Next setup the Mochiweb application:

-module(test_templates_web).

-export([start/1, stop/0, loop/2]).

start(Options) ->
    {DocRoot, Options1} = get_option(docroot, Options),
    Loop = fun (Req) ->
		   ?MODULE:loop(Req, DocRoot)
	   end,
    mochiweb_http:start([{name, ?MODULE}, {loop, Loop} | Options1]).

stop() ->
    mochiweb_http:stop(?MODULE).

loop(Req, DocRoot) ->
    "/" ++ Path = Req:get(path),
    case Req:get(method) of

	'GET' ->
           %% This call returns a list of nodes the Erlang application is connected to -
           %% a list like this: [node1@here.com,node2@here.com]
           NodeData = nodes(),

           %% Pass the data to the template
           Outty = index:render(NodeData),

           %% Send the output (String) back to the browser
           Req:ok({"text/html",Outty});

       _ ->
           Req:not_found()
    end.

Inside the ‘GET’ above, I pass the data to the compiled template, then send it back to the browser.

Obviously I’ve glossed over a few details, but hopefully you get the idea. It may not be as “elegant” as a Rails app, but it’s blazing fast!

Install Erlang on Ubuntu with Capistrano

Posted by Dave Bryson on May 05, 2008

Here’s a simple task that I use to install Erlang on remote servers using Capistrano and Deprec. Assuming you have an SSH key setup with the remote server, you can run this task from a terminal like this: “miceda:erlang:install”. This downloads the source and does the make/make install dance.

Capistrano::Configuration.instance(:must_exist).load do
 # install Erlang 12 on Ubuntu 7.10 (gutsy)
 namespace :miceda do
  namespace :erlang do
    SRC_PACKAGES[:erlang] = {
      :filename => 'otp_src_R12B-1.tar.gz',
      :dir => 'otp_src_R12B-1',
      :url => "http://www.erlang.org/download/otp_src_R12B-1.tar.gz",
      :unpack => "tar zxf otp_src_R12B-1.tar.gz;",
      :configure => %w(
        ./configure
        ;
       ).reject{|arg| arg.match '#'}.join(' '),
       :make => 'make;',
       :install => 'make install;'
    }

    desc "Install Erlang 12B-1"
     task :install do
       install_deps
       deprec2.download_src(SRC_PACKAGES[:erlang], src_dir)
       deprec2.install_from_src(SRC_PACKAGES[:erlang], src_dir)
     end

     desc "Install deps for Erlang"
      task :install_deps do
       apt.install( {:base => %w(libc6 libncurses5 libncurses5-dev libssl-dev openssl m4 libexpat1-dev)}, :stable )
      end

    end
  end
end

Of course the big benefit is that with Capistrano you can do this across several servers at the same time.