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Awful

Description

awful provides an application and an extension to ease the development of web-based applications.

Warning: this is alpha code. It certainly contains tons of bugs, since it hasn't been tested much, and the API is subject to changes.

Here's a short summary of awful features:

Author

Mario Domenech Goulart

Requirements

The following eggs are required:

Components

awful is composed by two parts: an application, which can be thought as a web server; and an extension, which provides most of the supported features.

A "Hello, world!" example

Here's a "Hello, world!" example to be run by awful (hello-world.scm).

  (use awful)
  
  (define-page (main-page-path)
    (lambda ()
      "Hello, world!"))

To run this example, execute:

 $ awful hello-world.scm

Then access localhost:8080 using your favourite web browser.

Without any configuration, awful listens on port 8080. Since awful uses Spiffy behind the scenes, you can configure the web server parameters using Spiffy's.

define-page is the primitive procedure to define pages. In the simplest case, it takes as arguments a path to the page and a procedure to generate the page contents. The path to the page you use as the first argument is the same to be used as the path part of the URL you use to access the page.

In the example we use the main-page-path parameter, which is one of the awful configuration parameters. The default is "/main". So, when you access http://localhost:8080 awful will take you to http://localhost:8080/main.

If you look at the page source code, you'll see that awful created an HTML page for you. Awful uses the html-tags's html-page procedure behind the scenes. You can customize the page either by passing html-page's keyword parameters to define-page or by setting the page-template parameter with your favourite procedure to generate pages (a one argument procedure which receives the page contents and returns a string representing the formatted contents). define-page would still pass the html-page keyword parameters, so you can make use of them.

You can also use some global page-related parameters if all pages use the same CSS, doctype and charset (page-css, page-doctype and page-charset, respectively).

Accessing request variables

Awful provides a procedure ($) to access variables from the request, both from the query string (GET method) and from the request body (e.g., POST method).

Here's a modified "Hello, world!" example to greet some person instead of the whole world:

  (use awful)
  
  (define-page (main-page-path)
    (lambda ()
      (++ "Hello, " ($ 'person "world") "!")))

The ++ procedure is an alias to string-append (name inspired by Haskell's operator to concatenate strings).

So, restart the web server to reload the code, then access the main page using an argument, represented by the person query string variable: http://localhost:8080/main?person=Mario. You'll see a page showing Hello, Mario!.

Re-evaluating the code by reloading the page

When we upgraded our "Hello, world!" example to the improved one which can use an argument passed through the URL, we needed to modify the code and restart the web server to reload the application code. Awful provides a way to reload the code via URL without restarting the server.

By default, the reload URL path is bound to /reload. So, to reload your code, add

(enable-reload #t)

and restart the awful server. Now, whenever you want to reload the application code, access http://localhost:8080/reload.

You can disable this feature by setting the enable-reload parameter to #f. You can also change the URL path by setting the reload-path parameter.

Using ajax

Awful provides a way to (hopefully) make the use of ajax straightforward for web applications.

By default, the ajax support is disabled, but it can be easily enabled by setting the enable-ajax parameter to #t. When you enable ajax, all the pages defined via define-page will be linked to the JQuery javascript library. The URL of the JQuery file can be customized by setting the ajax-library parameter (the default is Google's API JQuery file version 1.3).

When you have ajax enabled and you want to disable it for specific pages, you can pass #f as the value for the define-page keyword parameter no-ajax.

So, if we now change our code to

  (use awful)
  
  (enable-ajax #t)
  
  (define-page (main-page-path)
    (lambda ()
      (++ "Hello, " ($ 'person "world") "!")))

and reload the application, we'll have our page linked to JQuery.

Awful provides some procedures to do ajax. We start by the more generic one (ajax) to reply the page greetings when we click "Hello, <person>!".

  (use awful)
  
  (enable-ajax #t)
  
  (define-page (main-page-path)
    (lambda ()
      (ajax "greetings" 'greetings 'click
            (lambda ()
              (<b> "Hello, awful!"))
            target: "greetings-reply")
      (++ (<a> href: "#"
               id: "greetings"
               (++ "Hello, " ($ 'person "world") "!"))
          (<div> id: "greetings-reply"))))

The ajax procedure uses at least four arguments:

1. The URL path to the server-side handler (a string). This path is relative to ajax-namespace parameter (default is ajax. So, in the example, we'll have "/ajax/greetings" as the ajax path to be generated if we pass "ajax" as the first argument.

2. The ID of the DOM element to observe.

3. The event to be handled

4. The procedure to be run on the server-side.

So, in the example, ajax will bind the fourth argument (the procedure) to the first argument (the path) on the server side. Then it will add javascript code to the page in order to wait for click events for the element of ID greetings. When we click "Hello, <person>!", we'll get "Hello, awful!" printed on the page as reply. ajax updates the DOM element whose id is the value of the target keyword parameter ("greetings-reply", in the example).

For the very specific case of creating links that execute server side code when clicked, awful provides the ajax-link procedure. So our example could be coded like:

  (use awful)
  
  (enable-ajax #t)
  
  (define-page (main-page-path)
    (lambda ()
      (++ (ajax-link "greetings" 'greetings
                     (lambda ()
                       (<b> "Hello, awful!"))
                     target: "greetings-reply")
          (<div> id: "greetings-reply"))))

Adding arbitrary javascript code to pages

Awful provides a procedure which can be used to add arbitrary javascript code to the page. It's called add-javascript. Here's an example using javascript's alert and our "Hello, world!" example:

  (use awful)
  
  (enable-ajax #t)
  
  (define-page (main-page-path)
    (lambda ()
      (add-javascript "alert('Hello!');")
      (++ (ajax-link "greetings" 'greetings
                     (lambda ()
                       (<b> "Hello, awful!"))
                     target: "greetings-reply")
          (<div> id: "greetings-reply"))))

Database access

As with ajax, database access is not enabled by default. To anable it, you need to set the enable-db parameter to #t.

Additionally, to use the db, you need to provide the credentials. You can provide the credentials by setting the db-credentials parameter (see the postgresql egg).

To actually query the database, there's the $db procedure, which uses as arguments a string representing the query and, optionally, a default value to be used in case the query doesn't return any result. $db returns a list of lists. Below is an usage example:

  (use awful)
  
  (enable-db #t)
  (db-credentials '((dbname . "my-db")
                    (user . "mario")
                    (password . "secret")
                    (host . "localhost")))
  
  (define-page "db-example"
    (lambda ()
      (with-output-to-string
        (lambda ()
          (pp ($db "select full_name, phone from users"))))))

There's also the $db-row-obj procedure for when you want to access the results of a query by row name. $db-row-obj returns a procedure of two arguments: the name of the field and, optionally, a default value to be used in case the field value is #f.

  (define-page "db-example"
    (lambda ()
      (let ((& ($db-row-obj "select full_name, phone from users where user_id=1")))
        (<p> "Full name: " (& 'full_name))
        (<p> "Phone: " (& 'phone)))))

If you need more flexibility to query the database, you can always use the (db-connection) parameter to get the database connection object and use it with the procedures available from the postgresql egg API.

Login pages and session

Awful provides a very basic (awful?) support for creating authentication pages.

The basic things you have to do is:

1. Enable the use of sessions:

  (enable-session #t)

2. Set the password validation parameter. This parameter is a two argument procedure (user and password) which returns a value (usually #t or #f) indicating whether the password is valid for the given user. The default is a password which returns #f. Let's set it to a procedure which returns #t is the user and the password are the same:

  (valid-password?
    (lambda (user password)
      (equal? user password)))

3. Define a login trampoline, which is an intermediate page accessed when redirecting from the login page to the main page.

  (define-login-trampoline "/login-trampoline")

4. Create a login page. Awful provides a simple user/password login form (login-form), which we are going to use. Here's our full example so far (using the basic "Hello, world!" as main page).

  (use awful)
  
  (enable-session #t)
  
  (define-login-trampoline "/login-trampoline")    
  
  (valid-password?
    (lambda (user password)
      (equal? user password)))
  
  (define-page (main-page-path)
    (lambda ()
      "Hello world!"))
  
  (define-page (login-page-path)
    (lambda ()
      (login-form))
    no-session: #t)

That's the very basic we need to set an auth page. If the password is valid for the given user, awful will perform a redirect to the main page (main-page-path parameter) passing the user variable and its value in the query string . If the password is not valid, awful will redirect to the login page (login-page-path parameter)) and pass the following variables and values:

reason
the reason why awful redirected to the login page. It may be invalid-password, for when the password is invalid for the given user; or invalid-session for when the session identifier is not valid (e.g., the session expired).
attempted-page
the URL path to page the user tried to access, but couldn't because either he/she was not loged in or he/she provided an invalid session identifier.

Now we're gonna change our main page to store the user in the session and retrieve it to make the greetings message:

  (define-page (main-page-path)
    (lambda ()
      ($session-set! 'user ($ 'user))
      (++ "Hello " ($session 'user "world") "!")))

Here we can see the two procedures to access the session: $session and $session-set!.

$session-set! accepts two arguments: the first one is the name of the session variable and the second one is its value.

$session takes the name of the session variable as argument and returns its session value. We can optionally use a second argument to specify a default value, in case the session variable is not bound or is #f.

Session inspector

Awful provides a session inspector, so we can easily see the session contents for a given session identifier. By default, the session inspector is disabled. We can enabled it using the enable-session-inspector procedure, passing the session inspector URL path as argument:

  (enable-session-inspector "session-inspector")

Now, if you log in and try to access http://localhost:8080/session-inspector?sid=<paste the sid value here>, you'll get ... an access denied page.

Awful provides a way to control access to the session inspector (session-inspector-access-control parameter). The session-inspector-access-control parameter is an one-argument procedure which returns #f or some other value to indicate whether the access to the session inspector is allowed or not. By default, it blocks all access. Let's configure it so we can access the session inspector from the local machine (whose IP number is 127.0.0.1):

  (session-inspector-access-control
   (lambda ()
     (member (remote-address) '("127.0.0.1"))))

Regarding to the access denied message, you can customize it by setting the session-inspector-access-denied-message.

Now we can access http://localhost:8080/session-inspector?sid=<paste the sid value here> and see the session contents.

Web REPL

For further run-time, server-side web hacking, awful provides a REPL that you can use via web browser. The activation and control access are basically the same as for the session inspector. The relevant procedure and parameters are:

Pages access control

To allow/deny access to pages, you can use the page-access-control parameter. It's an one-argument procedure (the page path) which can be set to determine if the access to the page is allowed or not.

The example bellow shows a very silly access control to the main page: it only allows the access when the value of the request variable user is "mario":

  (use awful)
  
  (enable-session #t)
  
  (define-login-trampoline "/login-trampoline")
    
  (valid-password?
   (lambda (user password)
     (equal? user password)))
  
  (page-access-control
   (lambda (path)
     (and (equal? ($ 'user) "mario")
          (equal? path (main-page-path)))))
   
  (define-page (main-page-path)
    (lambda ()
      "Hello world"))
  
  (define-page (login-page-path)
    (lambda ()
      (login-form))
    no-session: #t)

You can customize the access denied message by setting the page-access-denied-message with an one-argument procedure (the page path).

Compiled pages

Since Chicken is a compiler and our pages are Chicken code, we can compile them to have faster pages. We just need to compile your app and pass the generated .so to the awful application:

 $ csc -s hello-world.scm
 $ awful hello-world.so

Multiple applications support

To be able to deploy multiple awful applications with different configurations under the same server, use Spiffy access files. See Spiffy's access files documentation for further details.

List of user configurable parameters

[parameter] (debug-file [file path])

If #f, indicates that debugging should be disabled. When set to a string, it should be the path to the file where the debug messages go (when debug or debug-pp is used.)

The default value is #f.

[parameter] (debug-db-query? [boolean])

When not #f, all queries passed to $db and to $db-row-obj are printed to the debug file.

The default value is #f.

[parameter] (debug-db-query-prefix [string])

Prefix to be used for queries debugging when debug-db-query is not #f.

The default value is "".

[parameter] (db-credentials [boolean or list])

Credentials to be used to access the database (see the postgresql egg documentation.) When #f, no database access is performed.

The default value is #f.

[parameter] (ajax-library [string])

URL or path to the ajax library (currently only JQuery is supported.)

The default value is "http://ajax.googleapis.com/ajax/libs/jquery/1.3/jquery.min.js"

[parameter] (enable-ajax [boolean])

When #t, makes define-page link the ajax-library to the generated page.

The default value is #f

[parameter] (ajax-namespace [string])

Name to be used as a namespace for ajax URL paths.

The default value is "ajax".

[parameter] (enable-session [boolean])

When #t, session support is enabled.

The default value is #f.

[parameter] (page-access-control [procedure])

An one-argument (URL path of the current page) procedure which tells whether the access to the page is allowed or not.

The default value is (lambda (path) #t).

[parameter] (page-access-denied-message [procedure])

An one-argument (URL path of the current page) procedure which returns the access denied message.

The default value is (lambda (path) (<h3> "Access denied.")).

[parameter] (page-doctype [string])

The doctype (see the doctype egg) to be applied to all pages defined by define-page. Can be overwritten by define-page's doctype keyword parameter.

The default value is "".

[parameter] (page-css [boolean or string])

The CSS file to be linked by all pages defined by define-page. Can be overwritten by define-page's css keyword parameter. See html-utils's html-page procedure to know about the css keyword parameter syntax.

The default value is #f (no CSS).

[parameter] (page-charset [boolean or string])

The page charset to be used by all pages defined by define-page. Can be overwritten by define-page's charset keyword parameter. The default value is #f (no explicit charset).

[parameter] (login-page-path [string])

The URL path for the login page. When creating a login page, be sure to set the no-session keyword parameter for define-page to #t, otherwise you'll get an endless loop.

The default value is "/login".

[parameter] (main-page-path [string])

The URL path to the app main page.

The default value is "/main".

[parameter] (app-root-path [string])

The base path to be used by the application. All the pages defined by define-page will use app-root-path as the base directory. For example, if app-root-path is set to "/my-app" and "my-page" is used as first argument to define-page, the page would be available at http://<server>:<port>/my-app/my-page.

The default value is "/".

[parameter] (valid-password? [procedure])

A two-argument (user and password) procedure which indicates whether the given password is valid for the given user.

The default value is (lambda (user password) #f).

[parameter] (page-template [procedure])

An one-mandatory-argument procedure to be used by define-page (unless define-page's no-template keyword parameter is set to #f) to generate HTML pages. Although this procedure can take only one mandatory argument, the following keyword arguments are passed:

The default value is html-page (see the html-page egg documentation.)

[parameter] (ajax-invalid-session-message [string])

The message to be used when attempting the make an ajax call using an invalid session identifier.

The default value is "Invalid session.

[parameter] (web-repl-access-control [procedure])

A no-argument procedure to control access to the web REPL.

The default value is (lambda () #f).

[parameter] (web-repl-access-denied-message [string])

Message to be printed when the access to the web REPL is denied.

The default value is (<h3> "Access denied.").

[parameter] (session-inspector-access-control [procedure])

A no-argument procedure to control access to the session inspector.

The default value is (lambda () #f).

[parameter] (session-inspector-access-denied-message [string])

Message to be printed when the access to the session inspector is denied.

The default value is (<h3> "Access denied.").

[parameter] (page-exception-message [procedure])

An one-argument procedure to be used when an exception occurs while define-page tries to evaluate its contents.

The default value is (lambda (exn) (<h3> "An error has accurred while processing your request."))

[parameter] (reload-path [string])

The URL path to the reload handler.

The default value is "/reload".

[parameter] (reload-message [string])

The message the reload handler prints after reloading the applications.

The default value is (<h3> "Reloaded.").

[parameter] (enable-reload [boolean])

When #t, disables applications reloading. Enables applications reloading otherwise.

The default value is #f.

[parameter] (enable-javascript-compression [boolean])

Enable javascript compression support. When enabled the compressor set by javascript-compressor is used.

The default value is #f.

[parameter] (javascript-compressor [procedure])

An one-argument procedure (the javascript code) which return the given javascript code compressed. Only used when enable-javascript-compression is not #f.

The default value is jsmin-string (see the jsmin egg.)

List of read-only parameters available to users

Note: these parameters should not be explicitly set and when their use is needed, it's a string sign you're doing something you shouldn't (except for db-connection, which can be used by procedures from the postgresql egg API).

[parameter] (http-request-variables)

The per-request value returned by spiffy-request-vars's request-vars.

[parameter] (db-connection)

A per-request postgresql egg connection object. The connection is automatically opened and closed by awful in a per-request basis (unless enable-db is #f or the no-db keyword parameter for define-page is #t.)

[parameter] (page-javascript)

Javascript code to be added to the pages defined by define-page.

[parameter] (sid)

The session identifier.

List of procedures

[procedure] (++ string1 string2 ... stringn)

A shortcut to string-append.

[procedure] (concat args #!optional (sep ""))

Convert args to string and intersperse the resulting strings with sep.

[procedure] (include-javascript file)

A shortcut to (<script> type: "text/javascript" src: file).

[procedure] (add-javascript . code)

Add arbitrary javascript code to the pages defined by define-page.

[procedure] (debug . args)

Print args, concatenated, to the file debug-file.

[procedure] (debug-pp arg)

Pretty-print arg to the file debug-file.

[procedure] ($session var #!optional default)

Return the value of var in the session (or default if var does not exist or is #f).

[procedure] ($session-set! var #!optional val)

If var is a quoted symbol, set the value of var to val. If val is not provided, var will have its value set to #f.

var can be an alist mapping session variable names to their corresponding values.

Examples:

  ($session-set! 'foo "foo value")

  ($session-set! '((foo . "foo value")
                   (bar . "bar value")
                   (baz . "baz value")))
[procedure] ($ var #!optional default converter)

Return the HTTP request value for the given variable var. The variable is looked for in both the query string (GET method) and request body (e.g., POST method).

[procedure] ($db q #!optional default)

Execute the given query (q) on the database and return the result as a list of lists or default if the result set is empty.

[procedure] ($db-row-obj q)

Execute the given query q on the database and return an one-argument procedure which takes as argument the name of the database field to get the value.

Example:

  (let ((& ($db-row-obj "select full_name, phone from users where user_id=1")))
    (<p> "Full name: " (& 'full_name))
    (<p> "Phone: " (& 'phone)))
[procedure] (sql-quote . data)

Escape and quote the concatenation of data to be used in SQL queries.

[procedure] (define-page path contents #!key css title doctype headers charset no-ajax no-template no-session no-db no-javascript-compression)

Define an awful page. The css, title, doctype, headers and charset keyword parameters have the same meaning as http://chicken.wiki.br/eggref/4/html-utils's html-page.

If no-ajax is #t, it means that the page won't use ajax.

If no-template is #t, it means that no page template (see the page-template parameter) should be used.

If no-session is #t, it means that the page should not use session.

If no-db is #t, it means that the page should not use the database, even when enable-db is #t and db-credentials is not #f.

If no-javascript-compression is #t the javascript code for the page is not compressed, even when enable-javascript-compression is not #f.

[procedure] (ajax path id event proc #!key target (action 'html) (method 'POST) (arguments '()) js no-session no-db)

Generate javascript code to be added to the page defined by define-page. Return the generated javascript code (which usually is not useful, so should be discarded).

path is the URL path (a string) of the server side handler. This path is placed under the (app-root-path)/(ajax-namespace) path. So, if your app-root-path is "my-app", your ajax-namespace is "ajax" and you use "do-something" as the first argument to ajax, the URL for the server side handler would be "/my-app/ajax/do-something".

id (a quoted symbol) is the id of the DOM element to be observed.

event (a quoted symbol or a list) is the event(s) to be observed. If it is a quoted symbol (e.g., 'click), only this event will be bound. If event is a list of events, all the events from the list will be bound.

proc is a no-argument procedure to be executed on the server side.

The target keyword parameter is the id of the DOM element to be affected by the result of proc.

The method (a quoted symbol, usually 'GET or 'POST) keyword parameter is the HTTP method to be used by the ajax request.

The arguments keyword parameter is an alist mapping request variables (symbols) to their values (strings). ajax uses these arguments to assembly the query string or the request body to send to the server when performing the ajax request.

Example:

   arguments: '((var1 . "$('#var1').val()")
                (var2 . "$('#var2').val()"))

If the no-session keyword parameter is #t, it means that no session should be considered (ajax implicit sends the session identifier when no-session is #f).

If the no-db keyword parameter is #t, it means that the should be no attempt to connect the database, even when enable-db is #t and db-credentials is not #f.

The ajax procedure is session, HTTP request and database -aware.

[procedure] (periodical-ajax path interval proc #!key target (action 'html) (method 'POST) (arguments '()) js no-session no-db)

Periodically execute proc on the server side, using (app-root-path)/(ajax-namespace)/path as the URL path for the server side handler.

interval (a number) is the interval between consecutive executions of proc, in milliseconds.

The meaning of the keyword parameters is the same as for ajax's.

[procedure] (ajax-link path id text proc #!key target (action 'html) (method 'POST) (arguments '()) js no-session no-db (event 'click))

A shortcut to

  (begin
    (ajax path id 'click proc ...)
    (<a> href: "#" id: id text))

The meaning of the keyword parameters is the same as for ajax's.

The event keyword parameter syntax is the same for ajax's event mandatory parameter.

[procedure] (login-form #!key (user-label "User: ") (password-label "Password: ") (submit-label "Enviar"))

Return a user/password login form (e.g., for using in authentication pages).

[procedure] (enable-web-repl path #!key css title)

Enable the web REPL. path is the URL path to the web REPL.

The keyword parameter css is the CSS to be used the the web REPL page (see html-utils's html-page documentation for the css keyword parameter.)

The keyword parameter title (a string) is the title for the web REPL page (see html-utils's html-page documentation for the title keyword parameter.)

enable-web-repl automatically enables ajax (see enable-ajax.)

[procedure] (enable-session-inspector path #!key css title)

Enable the session inspector. path is the URL path to the session inspector.

The keyword parameter css is the CSS to be used the the session inspector page (see html-utils's html-page documentation for the css keyword parameter.)

The keyword parameter title (a string) is the title for the session inspector page (see html-utils's html-page documentation for the title keyword parameter.)

enable-session-inspector automatically enables session (see enable-session.)

[procedure] (define-login-trampoline path #!key vhost-root-path hook)

Define a trampoline -- an intermediate page accessed when redirecting from the login page to the main page.

The name

Awful doesn't mean anything special. It's just awful. But folks on freenode's #chicken (IRC) have suggested some acronym expansions:

Acknowledgements (IRC nicknames on freenode's #chicken):

License

BSD

Version history
0.5
Reload handler register the reload path after reloading.
0.4
disable-reload? renamed to enable-reload. enable-reload is #f by default.
0.3
awful (the server) allows applications to use Chicken syntax (use, include etc)
0.2
Added javascript compression support
0.1
Initial release