Bluish Coder

Programming Languages, Martials Arts and Computers. The Weblog of Chris Double.


2007-11-21

Writing Web Applications in Factor

There was a request on #concatenative for information on how to write web applications in Factor. I went through a few steps on how to get started. I'm repeating it here for others that might be interested.

There are a number of different ways of writing web applications in Factor but for this approach I'm using the furnace framework.

The first step is to start the web server. This lives in the vocab 'http.server':

USE: http.server
[ 8888 httpd ] in-thread

This will start an instance of the server on port 8888 in another thread, to allow us to continue to enter commands in the listener.

By default web applications are accessed on the URL path /responder/name, where 'name' is the name of the web application.

Accessing the web application path runs an 'action'. An action produces HTML output which gets sent back to the client browser. A web application has a default 'action' that gets run (the equivalent of an index.html), and can have other actions that are specified in the URL. Some examples:

http://localhost:8888/responder/foo
Runs the default action for the 'foo' web application
http://localhost:8888/responder/foo/doit
Runs the 'doit' action
http://localhost:8888/responder/foo/hello?name=chris
Runs the 'hello' action giving the argument 'name' with the value 'chris'

The syntax for furnace URL's is therefore http://servername:port/responder/{webappname}/{action}?{arguments}

Furnace web application must exist under the 'webapps' vocabulary. So accessing /responder/foo will look for furnace details in the vocabulary 'webapps.foo'.

A furnace web application is registered with the http server using the 'web-app' word. It takes three arguments on the stack:

\ web-app effect-in . 
=> { "name" "default" "path" }

The 'name' is the vocabulary name of the web application with out the 'webapps.' prefix. 'default' is the name of the action that gets run when the web application URL is accessed. 'path' is the location of any template files the web application uses.

An action is a word that outputs data to be sent to the browser. It can be as simple as:

: doit ( -- ) serving-text "I am here" print ;

The word must be registered as an action:

\ doit { } define-action

Now accessing the URL for the web application with 'doit' at the end of the path will result in 'I am here' being sent to the browser. Note the 'serving-text' call. That outputs the headers for the mime type and the standard HTTP response. There is also a 'serving-html', or you could write the headers manually.

Actions can take arguments. These are placed on the stack for the word that is called:

: hello ( name -- ) serving-text "Hello " write print ;
\ hello { { "hello" } } define-action

So the complete code for the simplest of web applications is:

USE: http.server
[ 8888 httpd ] in-thread
IN: webapps.test
USE: furnace

: index serving-text "We're alive!" print ;
\ index { } define-action 

: hello ( name -- ) serving-text "Hello " write print ;
\ hello { { "name" } } define-action

"test" "index" "." web-app

Accessing http://localhost:8888/responder/test will run the 'index' action. This is what we passed as the 'default' parameter on the stack to the 'web-app' word. Accessing http://localhost:8888/responder/test/hello?name=chris will run the 'hello' action.

There is also the facility to have template files, very much like JSP. The 'path' parameter to 'web-app' defines the location of these. Inside your action word you can call 'render-template' to run the template and have it sent to the browser:

: runme ( -- ) f "page" "Title" render-template ;
\ runme { } define-action

This will load the 'page.furnace' file in the path given to 'web-app'. It should contain standard HTML with embedded Factor code inside <% and %> tags. It will be run and sent to the client. The 'f' passed in this example can be an instance of a tuple (an object) and the template can access the slots of that instance to display data, etc.

There is quite a bit more that can be done. There is a continuation based workflow system, validators for actions, etc. There is also much more that needs to be done. handling sessions, cookies, etc. Hopefully this post gives a quick introduction and allows you to get started.

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