Just enough Webmachine

Getting a solid foundation for your Zotonic skillset.

WHY

Zotonic talks to the web through a wonderful Erlang-based http REST toolkit called Webmachine. Webmachine was generously contibuted to the open-source world by Basho of Cambridge, MA.

A basic understanding of Webmachine will provide a solid foundation for your Zotonic skillset.

This Cookbook recipe will give you hands-on experience with Webmachine, Webmachine resources, and how to modifify a Webmachine resource.

ASSUMPTIONS

You have git, a recent version of Erlang, and Zotonic installed on your system.

You have basic Linux shell and program editing competencies.

You have basic sequential Erlang skills and understand the structure of Erlang modules.

HOW

We’ll install and compile Webmachine, create a simple demo application, and modify and execute a Webmachine resource. Finally, we’ll take a brief look at how Zotonic integrates Webmachine.

NOTE: Your Zotonic install already includes a webmachine instance. But we’ll install another instance so you can play.

What is Webmachine?

Webmachine handles well-formed http REST requests, gracefully handles all errors, and provides powerful debugging tools.

A Webmachine application is a set of resources written in Erlang, each of which is a set of functions over the state of the resource.

Note: in Zotonic’s version of Webmachine, we renamed resource to controller, as we think that’s a better name for those things. And in Zotonic, resources are “pages”.

These functions give you a place to define the representations and other Web-relevant properties of your application’s resources

How can I explore Webmachine?

Make sure that you have a working Erlang/OTP release, R12B5 or later.

Get the webmachine code:

git clone git://github.com/basho/webmachine

Build webmachine:

cd webmachine
make

Create, build, and start the skeleton resource:

./scripts/new_webmachine.sh mywebdemo /tmp
cd /tmp/mywebdemo
make
./start.sh

You should see a series of progress reports. Point a web browser at http://localhost:8000/

You should now see Hello, new world

How can I stop the demo?

Press ctl C, then press a

How can I examine the resource that produced the hello-world message?

In the shell:

$ cd /tmp/mywebdemo/src

Open mywebdemo_resource.erl in your favorite code editor.

How can I modify the resource to execute and display my own Erlang function?

Make the following changes mywebdemo_resource.erl just under the init/1 function:

earthman() ->
    "Earth man!".

to_html(ReqData, State) ->
    {"<html><body>Hello, " ++ earthman() ++ "<body></html>", ReqData, State}.

Save, and compile:

mywebdemo$ make

Now, from your web browser, refresh http://localhost:8000. You should see your change.

You’ll find more Webmachine documentation at: http://webmachine.basho.com/docs.html. It’ll take you pretty much wherever you want to go.

You now know enough about Webmachine to understand how Zotonic communicates through the web.

So how does Zotonic integrate Webmachine? Peek into your Zotonic deps directory:

$ cd /home/zotonic/zotonic/deps

You’ll see the``webzmachine`` directory, which is Zotonic’s version of webmachine It’s contents will be quite familiar from your explorations above, although some implementation details differ.