This is the 15th of the HARC Stack essays. Previous <=
Don’t forget – HARC Stack combines HTMX with raku Air, Red and Cro to supply a fresh approach to web development.
Two weeks ago, back before HARC Stack became the darling child of https://raku.org fame, we had been Forming. Most of the features of Air::Form were covered in that episode, but Validating was skipped since that is a topic in its own right.
Air::Form
Once again, here’s a top level view of the Air::Form code from Air::Examples.
Validating
Let’s zoom in on the form is validated trait:
has Str $.first-names is validated(%va<names>);
has Str $.last-name is validated(%va<name>) is required;
has Str $.email is validated(%va<email>) is required is email;
has Str $.city is validated(%va<text>); The is validated trait comes from the Cro::WebApp::Form class.
As the docs say:
… server-side validation at the field level can be specified by using the is validated($match-me, ‘Message’) trait, which will use the given validation error message if the input values fails to smartmatch against the condition. For example, it could be used with a regex:
has $.username is validated(/^<[A..Za..z0..9]>+$/, 'Only alphanumerics are allowed');
So that’s a regex and an error Str .
Air::Form disables client side (browser) field validation since (i) the overlap with server side validation can be disorienting and (ii) the browser side validation UI is hideous.
Regex
If you are familiar with regex (regular expression) syntax, feel free to skip this section.
Here’s a breakdown…
# This regex:
my regex alpha-num { ^<[A..Za..z0..9]>+$ }
# Explanation:
# ^ # anchor: start of string
# <[A..Za..z0..9]> # a character class including:
# # A..Z → uppercase A through Z
# # a..z → lowercase a through z
# # 0..9 → digits 0 through 9
# + # one or more of the above characters
# $ # anchor: end of string
# So it matches a string made only of alphanumeric characters, 1+ long.
say "Hello123" ~~ /<alpha-num>/; # True
say "hi_there" ~~ /<alpha-num>/; # Nil (underscore not allowed)
say "" ~~ /<alpha-num>/; # Nil (empty string not allowed)A regex is a character level language that does pattern matching against strings – either it matches the provided text, or if not rejects it. The ~~ operator is used to apply the regex to a string resulting in a matcher object. For more details dive into the Raku documents here.
Validating form fields ensures that the data users submit is safe, consistent, and free from malicious input. It protects applications from security risks while also enforcing rules like proper formats for emails, numbers, or passwords. Good validation improves user experience by catching errors early and keeping stored data clean and reliable.
Batteries Included
The following validators are provided with Air::Form (via the Hash constant %va – error text removed for clarity):
constant %va = (
text => /^ <[A..Za..z0..9\s.,_#-]>+ $/,
name => /^ <[A..Za..z.'-]>+ $/,
names => /^ <[A..Za..z\s.'-]>+ $/,
words => /^ <[A..Za..z\s]>+ $/,
notes => /^ <[A..Za..z0..9\s.,:;_#!?()%$£-]>+ $/,
postcode => /^ <[A..Za..z0..9\s]>+ $/,
url => /^ <[a..z0..9:/.-]>+ $/,
tel => /^ <[0..9+()\s#-]>+ $/,
email => /^ <[a..zA..Z0..9._%+-]>+ '@'
<[a..zA..Z0..9.-]>+ '.'
<[a..zA..Z]> ** 2..6 $/,
...
);It is easy to add your own validators. Just go %va<myval> = /regex/, ‘text’; … and the examples here are easy to copy and extend. More sophisticated validation schemes can be expected in future with the application of raku Grammars.
Next Time on this Channel
We are winding up this first series on HARC stack soon … next [& hopefully last] time the topic is Defaulting. Going forward there is more to do – user credentials, blog posts, CRUD and so on.
Thank you for watching this channel. Even better, review the Getting Started advice and try it out for yourself.
As usual, comments and feedback welcome. We are a friendly bunch over on the raku IRC chat and Discord.
~librasteve
