beer planet » PHP

How To: Disable/Block External HTTP Requests In WordPress

Artem Russakovskii — Wed, 16 Nov 2011 18:57:43 +0000

One thing that's been continuously annoying me when doing WordPress development on the go is when something somewhere inside WordPress decides to send requests to external urls when I don't even have Internet connection or it's slow and flaky (tethering, slow Wi-Fi, etc). This results in random lag when loading pages, especially if I haven't opened my dev WordPress instance for a long time.

Turns out there's an easy and undocumented (other than in code) solution. To block external HTTP requests right in WordPress's core itself, open up wp-config.php and add WP_HTTP_BLOCK_EXTERNAL like so:

1	define('WP_HTTP_BLOCK_EXTERNAL', true);

Whenever this variable is present, external requests will be ignored, unless you specify your own comma-separated whitelist of domains using WP_ACCESSIBLE_HOSTS like so:

1	define('WP_ACCESSIBLE_HOSTS', 'site1.com, site2.com');

You can examine relevant core code here and the relevant bug reports here and here.

Happy developing!

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How To Dynamically Increase Memory Limits When Interfacing With WordPress Using XML-RPC (Windows Live Writer, Etc)

Artem Russakovskii — Sat, 06 Nov 2010 09:00:44 +0000

Today's snippet is tremendously helpful if you are using an XML-RPC WordPress interface to read and publish your articles and are running into 500 Server Error issues due to running out of memory, manifesting themselves in something like this error message: "Invalid Server Response – The response to the metaWeblog.newMediaObject method received from the weblog server was invalid".

For example, my regular PHP memory allocation is 32MB or so, but if I load up Windows Live Writer, my favorite publishing tool, and ask it to load 1000 of the latest blog posts, I will undoubtedly get a server error back.

One solution would be to increase the memory allocated to PHP to something higher, like 256MB, which is how I used to get around the issue. I say "get around" because it's not a good solution – if someone finds a page that uses a lot of memory on your site, they could easily kill not only your web server but the whole machine due to swap death. Keeping a lower memory limit allows you to run your web server, such as Apache, with more children, thus serving more requests without getting overloaded.

So, I've looked into the WordPress core and came up with what I think is a proper fix – dynamic memory limit tweaking when dealing with XML-RPC only. Here is the code – add it to your functions.php and you should be golden:

/**
* Dynamically increase allowed memory limit for XML-RPC only.
*
* @param array $methods
* @return array
*/
function my_xmlrpc_methods($methods) {
  ini_set('memory_limit', '256M');
  return $methods;
}
add_action('xmlrpc_methods', 'my_xmlrpc_methods');

The code is pretty self-explanatory: it hooks into a WordPress hook that fires only for XML-RPC requests and adjusts the memory limit on the fly. No more out of memory errors and I'm able to load 1000 posts in Windows Live Writer without problems.

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How To Add Shortcode Support To WordPress Comments And Sidebar Widgets

Artem Russakovskii — Sat, 16 Oct 2010 03:20:26 +0000

WordPress has a great way of letting you use simple text tags called shortcodes to provide a whole bunch of functionality, including custom PHP code. In this article, I'm assuming that you already know what shortcodes do and how they operate (if you don't, head over here: Shortcode_API).

One glaring omission in the way shortcodes are set up by default is that they only get triggered in the content of your post, leaving the sidebar and comments out. I'm sure this is done for security, so that your readers can't screw something up by posting shortcodes they're not supposed to – after all, shortcodes are PHP snippets on the backend.

However, let's assume you really know what you're doing and you want, for example, to allow certain shortcodes in the comments and all shortcodes in the sidebar. It's your site and you should be able to do whatever you want with it. For instance, I wanted to provide a way to include QR codes using a [qr] shortcode syntax that I'd written both in the sidebar and in the comments, except in the comments that was the only shortcode I wanted to allow my readers to use.

Since these cases can get complicated, let's start simple and then progressively get deeper.

Allow all shortcodes in the sidebar

Assuming you want to enable shortcodes in the PHP Code Widget widgets (I believe this is the most common way to add PHP support to the sidebar), use this code:

1	add_filter('widget_execphp', 'do_shortcode');

If you have some other widgets in mind, you have to find out the right filter and use it just like above.

Allow only whitelisted shortcodes in the comments

Since I don't want all shortcodes to fire here, things get slightly trickier.

function init_common_shortcodes() {
  add_shortcode('qr', 'my_shortcode_qr');
}
 
function init_comment_shortcodes() {
  remove_all_shortcodes();
  init_common_shortcodes();
  add_filter('comment_text', 'do_shortcode');
}
 
init_common_shortcodes();
add_filter('comments_template', 'init_comment_shortcodes');

The code above will remove all shortcodes when it gets to comments and reinitialize only the whitelisted one called "[qr]", which is exactly what I wanted.

Note: If your code somehow uses shortcodes after the comments (such as a sidebar or a custom post query), you will need the trick in the next section.

Allow all shortcodes in the sidebar AND only whitelisted ones in the comments

At this point, things get slightly tricky because if I combine the previous 2 solutions into 1, by the time WordPress gets to the sidebar, it'll be left without any shortcodes at all – they've been removed by the code dealing with comments. Therefore, I need to save the shortcodes before dealing with comments and then restore them after the comments and before the sidebar.

function my_remove_all_shortcodes() {
  global $shortcode_tags;
  global $temp_shortcode_tags;
  $temp_shortcode_tags = $shortcode_tags;
  remove_all_shortcodes();
}
 
function my_restore_all_shortcodes() {
  global $shortcode_tags;
  global $temp_shortcode_tags;
  if(!empty($temp_shortcode_tags)) {
    $shortcode_tags = $temp_shortcode_tags;
  }
}
 
function init_common_shortcodes() {
  add_shortcode('qr', 'my_shortcode_qr');
}
 
function init_comment_shortcodes() {
  my_remove_all_shortcodes();
  init_common_shortcodes();
  add_filter('comment_text', 'do_shortcode');
}
 
add_filter('comments_template', 'init_comment_shortcodes');
add_filter('dynamic_sidebar', 'my_restore_all_shortcodes');
add_filter('widget_execphp', 'do_shortcode');
init_common_shortcodes();

Here is what the code does:

Initialize custom shortcodes that I want to add all over the place.
When WP gets to the comment block, it removes all shortcodes (again, for security) and re-initializes only the ones I want, but this time remembers them so that they can be restored later.
After the comments, when WP gets to the dynamic sidebar, it restores all the shortcodes and applies them to each PHP Code Widget.

And there you have it. Of course, the code may need tweaking for your own scenario but the ideas are all there. If you spot an error or know of an easier/better way, please let me know.

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How To Fix Intermittent MySQL Errcode 13 Errors On Windows

Artem Russakovskii — Tue, 05 Jan 2010 10:49:33 +0000

The Problem

I've had MySQL on my Windows 7 laptop for a bit (as part of wampserver), mostly for local offline WordPress development.

However, even though MySQL is relatively stable, I've been observing a vast quantity of intermittent MySQL errors, as reported by WordPress in the PHP error log (C:\wamp\logs\php_error.log). Here are some examples:

[05-Jan-2010 09:47:51] WordPress database error Error on delete of
'C:\Windows\TEMP\#sql17e0_1a2_6.MYD' (Errcode: 13) for query SELECT t.*, tt.*
FROM wp_terms AS t INNER JOIN wp_term_taxonomy AS tt ON tt.term_id = t.term_id
INNER JOIN wp_term_relationships AS tr ON tr.term_taxonomy_id =
tt.term_taxonomy_id WHERE tt.taxonomy IN ('category') AND tr.object_id IN (3)
ORDER BY t.name ASC made by require, require_once, include, get_footer,
locate_template, load_template, require_once, dynamic_sidebar,
call_user_func_array, widget_rrm_recent_posts, RecentPosts->execute,
ppl_expand_template, otf_categorylinks, get_the_category, wp_get_object_terms
 
[05-Jan-2010 09:50:42] WordPress database error Error on delete of
'C:\Windows\TEMP\#sql17e0_1b0_0.MYD' (Errcode: 13) for query  SELECT
SQL_CALC_FOUND_ROWS  wp_posts.* FROM wp_posts  INNER JOIN wp_term_relationships
ON (wp_posts.ID = wp_term_relationships.object_id) INNER JOIN wp_term_taxonomy ON
(wp_term_relationships.term_taxonomy_id = wp_term_taxonomy.term_taxonomy_id)
WHERE 1=1  AND wp_term_taxonomy.taxonomy = 'category' AND
wp_term_taxonomy.term_id IN ('3') AND wp_posts.post_type = 'post' AND
(wp_posts.post_status = 'publish' OR wp_posts.post_status = 'private') GROUP BY
wp_posts.ID ORDER BY wp_posts.post_date DESC LIMIT 0, 10 made by require, wp,
WP->main, WP->query_posts, WP_Query->query, WP_Query->get_posts

The important part here is "Errcode: 13", which is a file access error. The MySQL daemon process (mysqld.exe) randomly cannot access temporary tables it itself creates, which causes these errors and failed queries.

Digging Around

After looking around and finding nothing obvious, I tracked down a few forum posts mentioning the same issue.

Here is the gist – the problem is caused by an anti-virus program that is clearly not working properly.

The one mentioned on the forums is McAfee (big surprise, right? McAfee is a piece of junk – probably the worst anti-virus I've ever tried). In my case, however, it was the recently installed freeware security program from Microsoft called Microsoft Security Essentials, highly praised but problematic in this case nonetheless.

After thinking about it, I am confident that these security programs don't actually purposely prohibit access to the files MySQL creates. Instead, they lock these files for the duration of the check, so that the system doesn't get infected before they are approved. If you notice, the problems are related to temporary tables, created by MySQL on the fly. MySQL probably has a very short access timeout for these files, for performance reasons, and because it doesn't get this access fast enough, it considers it a failure (file deletions are failing, as you can see in the log).

The Solution

Now onto fixing the problem. The solution is to have Microsoft Security Essentials, in my case, or whatever your security program may be ignore these files.

You can block the whole Temp directory from being checked. It is not a good idea, as viruses can trickle down to that location and bypass your anti-virus:

Instead, you should just ignore by file extension: *.MYI and *.MYD. MySQL uses files with these extensions for its MyISAM table types. Using this approach is obviously safer as it doesn't single out a directory and instead targets specific files:

After I applied either of these exclusions, all MySQL Error 13 problems went away immediately.

Conclusion

The intermittent Error 13 problem on Windows is caused by 2 otherwise legitimate processes which, when mixed together, end up breaking MySQL.

Is this entirely the fault of the antivirus programs? Inadvertently, perhaps so.

Could MySQL be a bit smarter in this scenario? Perhaps so as well.

What do you, MySQL pros, think?

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Hidden Features Of Perl, PHP, Javascript, C, C++, C#, Java, Ruby, Python, And Others [Collection Of Incredibly Useful Lists]

Artem Russakovskii — Sun, 21 Jun 2009 19:38:56 +0000

Introduction

StackOverflow is an amazing site for coding questions. It was created by Joel Spolsky of joelonsoftware.com, Jeff Atwood of codinghorror.com, and some other incredibly smart guys who truly care about user experience. I have been a total fan of SO since it went mainstream and it's now a borderline addiction (you can see my StackOverflow badge on the right sidebar).

The Story

Update 6/21/09: This server is currently under very heavy load (10-200), even with caching plugins enabled. Please bear with me as I try to resolve the situation.

Feel free to bookmark this page and return to it later when the fires have been put out.

Update 06/21/09: I think I've got the situation under control now. The load is between 0 and 3 now and pages load relatively fast. I will be posting about the getting redditted/delicioused experience later.

Update 06/23/09: Added jQuery, Greasemonkey, Ruby on Rails, and Objective-C, broke databases into their own section, and sorted everything alphabetically.

Update 06/23/09: Added Scala, Lua, TCL, F#, Regex, and HTTP.

Update 07/21/09: Added ActionScript3/Flex, Erlang, PL/SQL, Silverlight, VBA, VHDL, WPF/XAML.

Update 10/24/09: Added Flash development/language/IDE, Emacs, Xpath/Xslt, Spring framework.

Update 01/18/10: Added Android (asked by yours truly), Qt, Django, Windows.Forms, R, Lisp, x86 assembly, Grails.

So, one day someone at StackOverflow started a "Hidden features of" post about a famous language (I don't feel like finding out which one was first exactly), and it turned out to be so popular that other posts in the same series started popping up.

Such questions were quickly turned into community wikis, for the purposes of harvesting and organizing information coming from the best developers on the planet and voted by users of the site. There are literally hundreds of answers, sorted by votes.

The Hidden Features series is great for people who are new to a certain language. It shows the ropes and tricks, all in one place, in the most concise manner possible. Even pros oftentimes find features of their favorite language that they'd never heard about.

beer planet » PHP

How To: Disable/Block External HTTP Requests In WordPress

How To Dynamically Increase Memory Limits When Interfacing With WordPress Using XML-RPC (Windows Live Writer, Etc)

How To Add Shortcode Support To WordPress Comments And Sidebar Widgets

Allow all shortcodes in the sidebar

Allow only whitelisted shortcodes in the comments

Allow all shortcodes in the sidebar AND only whitelisted ones in the comments

How To Fix Intermittent MySQL Errcode 13 Errors On Windows

The Problem

Digging Around

The Solution

Conclusion

Hidden Features Of Perl, PHP, Javascript, C, C++, C#, Java, Ruby, Python, And Others [Collection Of Incredibly Useful Lists]

Introduction

The Story

Hidden Features Of

Programming Languages

Databases

Mobile

Other

Hidden features of Bash – also see my bash cheatsheet.