You can find the full changelog here and get the latest version from the download page.

VLD is a tool that I started working on years ago to visualise the opcode arrays in PHP. Opcode arrays are what PHP's compiler generates from your source code and can be compared to assembler code that is generated by a C compiler. Instead of it being directly executed by the CPU, it is instead executed by PHP's interpreter.

Over the years I've been adding some functionality, also aided by Ilia and some others, to show more information. For example Ilia has added a more verbose dumping format for opcodes (through the vld.verbosity setting) whereas I have added routines to find out which ops in oparrays can never be reached. A very simple example of the latter is shown here:

If we run the above through VLD with php -dvld.active=1 test.php, you'll see the following output (I removed the part about the script body itself):

Function test:
filename:       /tmp/test1.php
function name:  test
number of ops:  9
compiled vars:  none
line     # *  op           fetch  ext  return  operands
---------------------------------------------------------
   2     0  >   EXT_NOP
   4     1      EXT_STMT
         2      ECHO                           'Hello%21%0A'
   5     3      EXT_STMT
         4    > RETURN                         true
   7     5*     EXT_STMT
         6*     ECHO                           'This+will+not+be+executed.%0A'
   8     7*     EXT_STMT
         8*   > RETURN                         null

End of function test.

Every opcode that has a * after the number (like in 5*) is code that can not be reached, and can possibly be eliminated from the oparrays in an optimiser.

The dead code analysis routines have also made their way into Xdebug which uses them for the code coverage functionality to highlight dead code. This mostly makes sense if you are running your code coverage together with unit tests such as you can do with PHPUnit.

Recently I've been working on some new functionality to visualise all the code paths that make up each function. These new routines sit on top of the routines that do dead code analysis. Every branch instruction (such as if, but also for and foreach) is analysed and a list of branches is created. Each branch contains information about the line on which the branch starts, the starting and ending opcode numbers that belong to the branch, as well as to which other branches this branch can jump to. There can be either no linked branches (when for example a return or throw statement is found), one linked branch (for an unconditional jump) or two linked branches (on a branch instruction). However, you need to be aware that internally, PHP's opcode don't always reflect the source code exactly.

Once all the branches and their links are found, another algorithm runs to figure out which paths can be created out of all the branches. It is best to illustrate this with an example. So let us look at the following script:

In this script we have a for-loop with a nested if construct. When we run this script through VLD (with php -dvld.verbosity=0 -dvld.dump_paths=1 -dvld.active=1 test2.php) we get the following output (again, only the test() function and with some white space modifications):

Function test:
filename:       /tmp/test2.php
function name:  test
number of ops:  22
compiled vars:  !0 = $i
line     # *  op             fetch  ext  return  operands
-----------------------------------------------------------
   2     0  >   EXT_NOP
   4     1      EXT_STMT
         2      ASSIGN                             !0, 0
         3  >   IS_SMALLER                 ~1      !0, 10
         4      EXT_STMT
         5    > JMPZNZ                  9          ~1, ->18
         6  >   POST_INC                   ~2      !0
         7      FREE                               ~2
         8    > JMP                                ->3
   6     9  >   EXT_STMT
        10      IS_SMALLER                 ~3      !0, 5
   7    11    > JMPZ                               ~3, ->15
   8    12  >   EXT_STMT
        13      ECHO                               '-'
   9    14    > JMP                                ->17
  12    15  >   EXT_STMT
        16      ECHO                               '%2B'
  14    17  > > JMP                                ->6
  15    18  >   EXT_STMT
        19      ECHO                               '%0A'
  16    20      EXT_STMT
        21    > RETURN                             null

branch: #  0; line:  2- 4; sop:  0; eop:  2; out1:   3
branch: #  3; line:  4- 4; sop:  3; eop:  5; out1:  18; out2:   9
branch: #  6; line:  4- 4; sop:  6; eop:  8; out1:   3
branch: #  9; line:  6- 7; sop:  9; eop: 11; out1:  12; out2:  15
branch: # 12; line:  8- 9; sop: 12; eop: 14; out1:  17
branch: # 15; line: 12-14; sop: 15; eop: 16; out1:  17
branch: # 17; line: 14-14; sop: 17; eop: 17; out1:   6
branch: # 18; line: 15-16; sop: 18; eop: 21
path #1: 0, 3, 18,
path #2: 0, 3, 9, 12, 17, 6, 3, 18,
path #3: 0, 3, 9, 15, 17, 6, 3, 18,
End of function test.

This dump consists of a few different parts. First of all we can see some basic information containing the name, the number of ops (22) and the compiled variables. The second part is a dump of all the opcodes that make up this function. The last part contains information about all the branches and the possible paths. This information is a bit hard to visualize in its textual form, so I've also added some code that dumps this information to a file format that the GraphViz tool "dot" can use to create a pretty graph. For this we re-run the previous PHP invocation as php -dvld.dump_paths=1 -dvld.verbosity=0 -dvld.save_paths=1 -dvld.active=1 test2.php. This creates the file /tmp/paths.dot that "dot" can use. If we run dot -Tpng /tmp/paths.dot > /tmp/paths.png we end up with the following picture:

If we put this graph next to the code, we can explain how this works. Every branch is named by the number of the first opcode in that branch:

• op #1 is the assignment of $i in line 4.

• op #3 is the loop test in line 4. If the condition doesn't match, we jump to op #18 on line 16 that echos the newline.

• op #9 is the if condition on line 6.

• op #12 is when the if condition returns true and

• op #15 is when the if condition returns false.

• op #17 sits behind both op #12 and op #15 and makes sure there is a jump to the counting expression in #op 6.

• op #6 is the post increment operation on line 4 which will then again be followed by op #3 to check whether the end of the loop has been reached.

This is of course a very simple example, but it also works for (multiple) classes and functions in a file. You just need to make sure to tell VLD that you don't want the code executed as the output could be very large. You can use the vld.execute=0 php.ini setting for that.

I hope this new functionality can spread some light on how loops etc. work in PHP. In order to play with the code, you need to check-out VLD from my SVN with svn co svn://svn.xdebug.org/svn/php/vld/trunk vld. You can also view the code on-line at http://svn.xdebug.org/cgi-bin/viewvc.cgi/vld/trunk/?root=php. Look out for a new release coming soon!

Years ago I wrote about a Firefox extension that allows you to start an Xdebug debugging session by clicking on an icon in Firefox' status bar. For some unexplained reason, this extension is no longer available through Firefox' addon-site. Although I have a copy at http://xdebug.org/files/xdebug_helper-0.3.1-fx.xpi for archival purposes, there are now a few other browser extensions that do the same thing.

easy Xdebug

easy Xdebug is an extension that serves as a replacement for the now unavailable Xdebug helper extension. It's written by Brecht Vanhaesebrouck of eLime. The extension was originally tested with Netbeans but it also seems to work fine with Komodo.

Xdebug enabler

Xdebug enabler is an extension for Google's Chrome browser. It "allows you to enable and disable triggering Xdebug from with in Chrome. Useful if you are a web developer using an IDE that supports Xdebug like Eclipse with PDT." It's written by 'remailednet' and available through the Google Chrome Extensions website.

JavaScript 'enabler'

I also ran across a blog post by 'Caleb G' from HigherVisibility. Instead of making an extension for a specific browser, he outlines two JavaScript bookmarklets that allow you to start and stop an Xdebug debugging session.

I speak at many conferences and more and more of those conferences are using a service called joind.in. The joind.in website allows attendees of conferences to leave feedback for the speakers, organisers and sponsors. For me as a speaker this feedback by attendees is very important (as long as the comments are constructive). I use those comments to tweak and improve my presentations if I give them at a later moment.

The joind.in website also provides an API that allows you to talk to the service from other applications and sites. I've now integrated this in my site (at the talks page). It uses JQuery's ajax functionality to talk to the backend which queries (and caches) the joind.in API requests. In order to make API calls, you need to make POST requests to a specific URL. The URL depends on what type of object you want to use. For example, there is http://joind.in/api/talk for requesting information about talks, and http://joind.in/api/user for fetching information about users.

Requests can be either made in XML, or with JSON. A simple example to request all comments for a specific talk can be done with something like:

The do_post_request() code I lifted from Wez' page, and looks like:

 array(
                        'method' => 'POST',
                        'content' => $data
                )
        );
        if ( $optional_headers !== null) {
                $params['http']['header'] = $optional_headers;
        }
        $ctx = stream_context_create( $params );
        $fp = fopen( $url, 'rb', false, $ctx );
        $response = stream_get_contents( $fp );
        return $response;
}
?>

I am also fetching the full name for each user. Because this could mean that I have to do a lot of requests I am caching them with eZ Components' Cache component.

You can see the code operational on the talks page, by clicking on the little joind.in logo after each talk that is on the site. If JavaScript is disabled, the logo turns into a link that takes you to the joind.in site with all the comments.