Extending WordPress with (Web)Hooks

mitcho (Michael 芳貴 Erlewine)http://mitcho.com

September 28, 2009Boston WordPress Meetup

Today• Introduction• Modifying WordPress behavior• filters and actions

• Writing our first plugin in PHP• Extending WordPress with webhooks via HookPress

NOTE:• Will link to slides and code later on Meetup site

• Please rate later on SpeakerRate• again, link on Meetup.com

Introduction

Introduction• Hi, I’m mitcho.

Introduction• Hi, I’m mitcho.• Linguist, coder, teacher.

• At MIT. Previously at Mozilla.

• At MIT. Previously at Mozilla.• Programming PHP/MySQL since 2002?

• At MIT. Previously at Mozilla.• Programming PHP/MySQL since 2002?• Blogging (off and on) at mitcho.com since 2007.

• http://mitcho.com; @mitchoyoshitaka

Introduction

• Yet Another Related Posts Plugin

Introduction

• Yet Another Related Posts Plugin• ...aka YARPP

Introduction

• Yet Another Related Posts Plugin• ...aka YARPP• As seen on Laughing Squid, ma.tt...

Introduction

• Yet Another Related Posts Plugin• ...aka YARPP• As seen on Laughing Squid, ma.tt...• Over 250k downloads

Introduction

• Yet Another Related Posts Plugin• ...aka YARPP• As seen on Laughing Squid, ma.tt...• Over 250k downloads

• http://mitcho.com/code/yarpp or search for “YARPP”; @yarpp

WordPress

• Open-source, http://wordpress.org

WordPress

• Open-source, http://wordpress.org• PHP/MySQL

WordPress

• Open-source, http://wordpress.org• PHP/MySQL• Today: not wordpress.com

WordPress

• Self-hosted, so in theory you could modify it it directly

WordPress

• Self-hosted, so in theory you could modify it it directly• Not recommended!

WordPress

• Highly extensible plugin architecture

WordPress

• Highly extensible plugin architecture• WordPress itself uses it to modify its own behavior

Modifying behavior

• How does WordPress work?

Modifying behavior

• How does WordPress work?• Example: displaying a post’s content

Modifying behavior

parse URL

Modifying behavior

parse URL get content from db

Modifying behavior

parse URL get content from db display

Modifying behavior

• but it’s not actually that simple

Modifying behavior

• but it’s not actually that simple

smart quotes, paragraph splitting, HTML formatting, smilies...

get content from db display

Modifying behavior

I have the content and am about to display it. Who wants to modify it first?

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

Your customfunctions here:

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

wp_texturize

convert_smilies

wpautop

Modifying behavior

This is a filter pattern:multiple functions act asfilters on the same text/target.

Modifying behavior

Each such filter hook (= “pathway,” “process”) has a name. This one is called the_content.

Modifying behavior

• Every filter function must be registered against that filter hook ahead of time:

Modifying behavior

add_filter(“the_content”, “my_function_name”);

Modifying behavior

hook name

Modifying behavior

hook name function name

Modifying behavior

• There’s another kind of hook:

Modifying behavior

• There’s another kind of hook:• actions

Modifying behavior

• There’s another kind of hook:• actions• target certain “events” that occur.

Modifying behavior

• There’s another kind of hook:• actions• target certain “events” that occur.• Examples: a post is published, a comment is made, someone accesses wp-admin, etc.

Modifying behavior

• actions...

Modifying behavior

• actions...• don’t necessarily modify anything but can trigger other processes.

Modifying behavior

• actions...• don’t necessarily modify anything but can trigger other processes.

• can also produce output, modify the database, etc.

Modifying behavior

• filters...

Modifying behavior

• filters...• modify (filter) something and return it.

Modifying behavior

• The return value matters.

Modifying behavior

• The return value matters.• actions...

Modifying behavior

• The return value matters.• actions...• correspond to an “event.”

Modifying behavior

• The return value matters.• actions...• correspond to an “event.”• Return values don’t matter.

TodayNOTE:

TodayNOTE:• I’m using MAMP: Mac, Apache, MySQL, PHP.

TodayNOTE:• I’m using MAMP: Mac, Apache, MySQL, PHP.• Similar to XAMPP on Windows.

TodayNOTE:• I’m using MAMP: Mac, Apache, MySQL, PHP.• Similar to XAMPP on Windows.• Working on a server directly is okay too...

TodayNOTE:• I’m using MAMP: Mac, Apache, MySQL, PHP.• Similar to XAMPP on Windows.• Working on a server directly is okay too...• but avoid working on live sites.

Writing a plugin

Task: display a word count for posts

Writing a plugin

• PHP script

Writing a plugin

• PHP script• Place in wp-content/plugins/

Writing a plugin

• PHP script• Place in wp-content/plugins/• Requires a certain header

http://codex.wordpress.org/Writing_a_Plugin

Writing a plugin

The plan:1.Write a filter function which...a. takes the content as its input;b. counts the words;c. adds, for ex., <p>(43 words)</p> to the end of the content;

d. returns the modified content;

Writing a plugin

The plan:1.Write a filter function which...2.Register that function as a filter. Use the the_content filter hook.

Writing a plugin

Task (continued): add a sponsorship message

Writing a plugin

The plan (continued):3.Write an action function which prints the message.

4.Register it against the wp_footer action hook.

This is a filter...

...so it takes an argument...

This is a filter...

...so it takes an argument...

...and returns it after modifying.

This is an action...

...so it returns nothing.

Writing a plugin

• Right now the counting happens on the archive and front pages as well.

Writing a plugin

• Use the WordPress is_single() conditional tag.

Writing a plugin

• Use the WordPress is_single() conditional tag.• You may have seen such conditional tags in theme development.

Resources

• PHP manual: php.net

Resources

• PHP manual: php.net• Codex: codex.wordpress.org/Writing_a_Plugin and links there

Resources

• Forum: wordpress.org/support/forum/10

Resources

• Forum: wordpress.org/support/forum/10• The source: core.trac.wordpress.org/

Look into...

• Namespacing: use function_exists(), classes, unique names.

Look into...

• Saving options: get_option(), etc.

Look into...

• Saving options: get_option(), etc.• Adding an options screen: codex.wordpress.org/Adding_Administration_Menus

Look into...

• Security: use data validation for HTML, SQL queries, etc.

Look into...

• Security: use data validation for HTML, SQL queries, etc.• WordPress helps you: codex.wordpress.org/Data_Validation

Look into...

• Security: use data validation for HTML, SQL queries, etc.• WordPress helps you: codex.wordpress.org/Data_Validation

• Share! Consider uploading to wordpress.org/extend

Extending WordPress

• What if...

Extending WordPress

• What if...• you’re more comfortable in another language?

Extending WordPress

• What if...• you’re more comfortable in another language?

• you want to integrate WordPress with another system?

WordPress

+ HookPressWordPress

action!filter!

action!filter! your

script

local or remote

action!filter! your

script

local or remote

action!filter! POST your

script

local or remote

WordPress + HookPress

• create POST webhooks

• create POST webhooks• supports both actions...

• create POST webhooks• supports both actions...• create push notifications

• ...and filters

• ...and filters• extend WordPress without PHP

Get HookPress

• mitcho.com/code/hookpress• Screencast online

• Stay in touch!• @hookpress on twitter

Get HookPress

Resources

• Check the HookPress request:

Resources

• Check the HookPress request:• postbin.org

Resources

• Run basic/proxy scripts:

Resources

• Run basic/proxy scripts:• scriptlets.org

Resources

• General WebHooks information:

Resources

• General WebHooks information:• webhooks.org

Resources

Thank you!Questions?

Please rate the talk on SpeakerRate.

mitcho (Michael 芳貴 Erlewine)mitcho.com; @mitchoyoshitaka

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