Open Source

This article is dedicated for WordPress developers who has never used Subversion before and wanted to release their plugin to the public. Once you have submitted a form to WordPress. They will reply you with a email that contains your WordPress Subversion repository link. You do not have any knowledge of WordPress Subversion repository and don't know where to upload your new WordPress plugin to share with the public. You started searching for a solution around the internet for Solution without having any luck. Sad. Well, i go through that because i am those confuse people around the world who can't just read and read the whole article written with pure English. So here, some image picture for you to learn to access WordPress plugin Subversion repository. You can also read the whole Subversion book given by WordPress tutorial in command line.

Requirement to access WordPress Subversion

There are two ways of accessing WordPress plugin Subversion repository. The first one will be using pure command line instruction and the other way is to have a Subversion Client. I will show you the easy way to make life easier (the client is built for this purpose). Look at the picture below on Subversion website where all Subversion Client exist for different platform.
Download one of them depending on your platform and installed it to your system.

Working with Subversion Client

For this article, i will use TortoiseSVN for Windows users. You will have to fire up the installed TortoiseSVN on your PC and it will show you something like that below,

The application is informing you this is not the way to use Subversion repository. The correct way is to find the folder you wish to upload right-click it and select the application from the menu as shown below,

You can use the import function shown above to import straight to your Subversion repository or clicked on Repo-browser to upload them one by one. After you have done that just follow the instruction given by WordPress on where to upload the respective files to and you are done. Wait around 15--20min before it will show up on WordPress plugin search functionality. After this, use that particular folder to make your changes and work on your plugin in the future. After every changes you can just clicked on the same folder and pressed commit. If anything happen you can revert back your version from your previous committed version to see what you have changed. After you have all done with the new version do the same by copying to the Tag folder. Remember the to update the Stable tag in your readme.txt to reflect the changes.

P.S: you will only need to upload once in trunk and copy those files to tag/x.x.x.x to reflect the current version to your users. trunk is the version you will be working on and tag will be the one that inform others about your latest fixed/update on your plugin

Since i can't find this information anywhere on Google and WordPress search box, i will write a post out to save time for people who want to validate whether a person has logged into WordPress to access their external plugin page (another page that is not resist in WordPress Administrator panel).

Problem

My plugin has a file mangement page that help manage the site images from my plugin but the page was external and could be access by ANYONE as long as they have the URL, this is not secure at all. Thus, i wanted to know whether WordPress has any method or action hook that allow to validate a user upon entering that page. I tried Google and WordPress search box for any open question for this. Unfortunately, there isn't any.

Solution

In order to use methods exist in WordPress in an external page, we will have to include them into your page. The file i used to include in my page was 'wp-config.php' in WordPress. This will include all WordPress methods and dependency that these methods have so we won't have to worry that our plugin will just break suddenly.

The other important thing after the main page has been imported is the method. WordPress provides a method called 'is_user_logged_in()', with this method, we can validate whether that particular user has logged into WordPress to check whether they are the correct user. The following code illustrate the above explanation,

require_once '../../../../wp-config.php';
if ( is_user_logged_in() ) 
{
	echo "i am logged in";
}

This is jusst a demo so the real code of mine won't be here to confuse you. The require_once path used is just to navigate downwards. So any user of WordPress can access the page? Of course not! Using the following code we can validate which level of access the user has,

require_once '../../../../wp-config.php';
global $current_user;
get_currentuserinfo();
$level = $current_user->user_level;
if ( is_user_logged_in() && $level == "10") 
	echo "you have access";
else
	echo "you do not have access";

This way we will have to validate what access level this particular user has with the global variable $userdata, WordPress doc has demonstrate this pretty nicely and by checking its access level, you can restrict what level of user is allowed to access your page.

One problem i just came across while working on my WordPress plugin that many might not know is the danger of making mistakes on filter and the_content action hook. The importance of 'the_content' action hook and where this particular small sentence will affect your overall WordPress and caused it to malfunction if WordPress plugin developer used it carelessly (scary stuff). In this article, i will show you some of the mistake i made and what are the consequences in screen shot to inform WordPress plugin developers what will happen to WordPress when this two is being used wrongly.

What is 'the_content and filter?

In case you don't know what is filter and the_content action hook, filter is used in WordPress to filter the data between WordPress and its database. Short to say, you can manipulate the data retrieved from WordPress database before it shows out. The 'the_content' action hook is used to tell WordPress to print the content of the post, short to say, i am trying to manipulate the data from WordPress before displaying out to the end-user.

Problem

i have a test site which use to debug and test my plugin in a test environment before implementing it on the LIVE site. Everything goes well on the TEST since there is only one plugin but problem came when there are more than one plugin which hell can happen, not only deal to naming or method contradiction but some other unknown problem can occurred. One of the very rarely unforeseen problem is the filter and 'the_content' action hook problem. By the way, I am using WordPress v2.8 for testing.

Consequences

Many might not know what will 'the_content' affect the internal and external of WordPress (Many might aware of the external consequences but not the internal ones). Let's take a look at one of my plugin tester site (http://1sitedaily.com) who reported these problems to me. In the post page, she was typing the post and this particular red thing came out of no where!

This red post was either the previous post or the current post! It was caused by the use of 'the_content' action hook imappropriately (imagine how irritating will it be for the user). Once she clicked save as draft or worst when it suddenly auto save as draft and empty page is return!

Although the page was saved, this is not acceptable! Internally, this is what will happen to the Administration panel when 'the_content' action hook is not being used appropriately. Nonetheless, if this method is not used appropriately for the external part, the content might not even be showing!

This has missing content on the front page.

Same post with missing content on single page.

What happen?

So what really happen there? It is actually quite a silly mistake make by developers with PHP (even me) that usually forgotten by them when writing for a open source application. Deep in our mind, we think this is a new language with all the rule define by WordPress but its actually just PHP.The external mistakes was,

function article_example($content)
{
	if($content != "")
	{
		echo $content;
	}
	else
	{
		echo "NOTHING FOUND";
	}
}
add_filter('the_content', 'article_example');

Nothing seems wrong here, right? It will print out the relevant codes instructed on the template. But this is where the problem comes internally. Since filter event handler is also attached in the administration panel, anything that trigger 'the_content' in the administration panel will result in the above function execution (this means post page also uses 'the_content' to output the display we see on the editor). So, the red box appeared in WordPress was due to Ajax function being executed behind WordPress to save as draft and the function above was executed which duplicated a content out of the post. When the 'save as draft' button was clicked, a empty page (or any other words in the page which does not return the user back to the post page) was returned because the above function was executed and the echo statement was called. In PHP, during any execution or redirection was occurring, and echo statement will stop the page from redirecting. That is the main reason why the post page was not shown and other page appeared in front of the user.

The internal mistakes are something like this,

function article_example($content)
{
	$content = "The content contains: ".$content;
}
add_filter('the_content', 'article_example');

which the developers forgotten to output or return the correct value back to WordPress. The other thing that might occurs will be semantic errors or logic error.

Correct way of displaying filter and 'the_content'

Save yourself some time, in WordPress to echo a statement when using the filter statement ALWAYS use return,

function article_example($content)
{
	return "The content contains: ".$content;
}
 add_filter('the_content', 'article_example');

returning the value using filter will also resulting the display of the modified content! No problem will occurs like the above one when using return instead of echo although it also do the job!

This topic may seems stupid to some plugin developers but it may really surprise you. Most of you will just say, "Hey, just use the WordPress global variable, $post. Issue solved!". Yes, it is stated as global variable across WordPress developers and it should be globally available. Surprisingly, IT IS NOT~. I spend hours researching for an answer which are not document anywhere and finally decided to write a post to inform some plugin developer who are still unaware of such condition.

Problem

I wanted to attached a function to an event, publish_post whenever the user click on publish or update button when they have done with their post in WordPress. Usually, global variable $post will solve this problem easily. But for the case of publish_post action hook, this is not the case. The global variable $post which is accessible in any area of WordPress is not accessible when a user clicked on the publish button. The global variable $post will return 'null' instead of the post object which contain all the post data. Let the nightmare began.

Solution

Usually, we will see this on top of the post,

The URL of the post page contains the post ID! So the smart alex me try to be funny and use a $_GET['post'] to try retrieve the post id after i have failed miserably on the global variable, $post upon user clicked on publish button. With hope, it fail again. So i was thinking, maybe there exist some post data instead of a get data. So i try to use $_POST['post'] to retrieve the post id. Fail (expected). Since i am using a function to tried all these methods (post,get, global variable) as shown below,

function example()
{
global $wpdb;
global $post;
echo var_dump($post)."<br />";
echo $_POST['post']."<br />";
echo $_GET['post']."<br />";
}
add_action('publish_post', 'example');

There might be a problem retrieving global variable in my function so i try doing it outside the method as shown below,

global $post;
echo var_dump($post)."<br />";
echo $_POST['post']."<br />";
echo $_GET['post']."<br />";

function example()
{
global $wpdb;
global $post;
echo var_dump($post)."<br />";
echo $_POST['post']."<br />";
echo $_GET['post']."<br />";
}
add_action('publish_post', 'example');

It still fail! Nightmare. If you look at WordPress Plugin API, on the publish_post description it state this,

Runs when a post is published, or if it is edited and its status is "published". Action function arguments: post ID.

Action function arguments: post ID? Looks like using this action hook required a function argument post ID. So i tried this instead.

function example($post_ID)
{
global $post;
echo $post_ID."<br />";
echo var_dump($post)."<br />";
echo $_POST['post']."<br />";
echo $_GET['post']."<br />";
}
add_action('publish_post', 'example');

Surprisingly, i got it! The ID is retrieved this way! No global variable available if you are using publish_post action hook!

Conclusion

I believe the reason why the global variable,$post  is not available during publish_post action hook was because the details of the post has been updated by the user and the information in the global variable are not updated. Thus, only the ID is available in the global variable if there is one. So to avoid unnecessary usage of memory, the global variable, $post was not created instead. The WordPress version for this was 2.8. Hope this help out a bit.

In case some of you don't know what the title of this post means, it has to do with building plugin for WordPress. Let me explain  a little on what does an action means in WordPress. Basically, we can add a function to an action or event (whatever you called it) in WordPress to perform some task before or after the action or event has occured.

Problem

The reason why i bought this post up was because i nearly get frustrated working on my WordPress plugin because there wasn't any action listed in WordPress plugin API that stated an action that can be attached to an event before or after an excerpt is being bought out! Search all over the place, fail. So i decided to do a trial and guess with these action thing for my plugin to attached an event when an excerpt is being bought out.

Solution

In case you might not aware how a excerpt is being printed out on the template, they used

the_excerpt();

This will print out the excerpt in your WordPress. So i tried using the_excerpt to be placed into my WordPress add_action statement as shown below,

add_action('the_excerpt', 'hpt_attach_excerpt');

'hpt_attach_excerpt' is the function call when excerpt is being triggered. To my surprise, it work! But it will only display whatever the function, 'hpt_attach_excerpt' contains as shown below.

So where is my regular excerpt? It seems like if i attached a defined action used in WordPress that are not listed in the WordPress Plugin API, it will be overwritten by my own method 'hpt_attach_excerpt'. I digged again to find the method in WordPress site that will provide me with the missing excerpt i was looking for. Fail. So i digged into the source code of WordPress and managed to find the key method that return the excerpt of a post, get_the_excerpt(). get_the_excerpt() is the based method that retrieve the data from the database to the_excerpt for it to filter.  Now i write the code as follow,

function hpt_attach_excerpt()
{
echo "This is the function 'hpt_attach_excerpt' produce";
echo get_the_excerpt();
}
add_action('the_excerpt', 'hpt_attach_excerpt');

Looking back to the display to check whether the attachment has completed.

There it is! Both my function message and my excerpt message!

P.S: You can use add_filter if you do not wish to overwrite the default function of 'the_excerpt' function.

Conclusion

If you have read through the post, you might aware that this is not only restricted to adding action for excerpt. This shows that we can add any WordPress function that are not defined in WordPress Plugin API (Offical action available) as action and rewrite or append any type of instruction to the default action given by WordPress. Can't find your action needed to perform your WordPress plugin? You just found the answer! Hope this can help many developers who are working on their plugin! ( Thanks for all the wonderful plugin developed! )