...composed of an indefinite, perhaps infinite number of hexagonal galleries...

© 1994-2017. David Sklar. All rights reserved.

Degrees of Freedom

What do you think the following PHP snippet outputs?

$temperature = 74;
print "It is $temperature°F right now.";

Fixing Broken UTF-8

When working on the i18n bits of Learning PHP 7, I had a problem. My example showing how plain string functions such as strtolower() and strtoupper() mangle multibyte UTF-8 characters was making the book formatting/rendering pipeline barf. The processing tools are expecing nicely formatted, valid, UTF-8 encoded HTMLBook files. It didn’t like the mangled invalid UTF-8 characters in my example output.

To fix this, I wrote the following function to replace invalid UTF-8 sequences with the Unicode Replacement Character (U+FFFD):

Now I can keep the real invalid byte sequences in my raw book source code (which makes my automatic “does the output of this code example match what it’s supposed to?” checker happy) but end up with a nice � (constructed from three valid bytes) in the formatted output.

Default SSL/TLS in Different PHP Versions

How’s My SSL is neat. So is PsySH. Here’s how recent versions of PHP (via Homebrew) plus PHP 7 stack up:

PHP 5.5:

Psy Shell v0.5.0-dev (PHP 5.5.25 — cli) by Justin Hileman
>>> json_decode(file_get_contents(''))->rating;
=> "Bad"

PHP 5.6:

Psy Shell v0.5.0-dev (PHP 5.6.9 — cli) by Justin Hileman
>>> json_decode(file_get_contents(''))->rating;
=> "Probably Okay"

PHP 7:

Psy Shell v0.5.0-dev (PHP 7.0.0-dev — cli) by Justin Hileman
>>> json_decode(file_get_contents(''))->rating;
=> "Probably Okay"

Thanks, Daniel !

My Android Email Client

The blog post I wrote about why I stopped using Blue Mail (now called Type Mail) as my Android email client has gotten a lot more attention than I was expecting. I get a fair amount of email these days that essentially says “Woah! So what do you use?” This post is to answer that question!

I use K-9 Mail. It’s free, it’s open-source, it does the job. It even supports aliases.

I haven’t gotten GPG integration working yet, but otherwise I’m very happy with it.

If anyone has other thoughts, post this to Hacker News and let me know the URL and I’ll add a link for commenting.

PHP To Make You Smile

Does it make you smile or frown that the following is valid PHP?

class 😀 {

    public static function 😁() {
        print "😃";


My hypothesis is that your reaction is correlated with whether you think the T_PAAMAYIM_NEKUDOTAYIM thing is trivial and amusing or a wart that must be excised.

Converting a PHP Extension to HHVM

In a previous post I wrote about converting a PHP 5 extension to PHP 7. This article is about converting that same PHP 5 extension to work with HHVM.

The code changes to get things working were not very large – mostly just stylistic tidying to make the C++ compiler happy – but I found the process much more difficult than the PHP 7 conversion just due to unfamiliarity with HHVM and its uneven documentation.

Because building HHVM itself is such a time-consuming beast, I chose to implement my module as a dynamic extension in the style of the DSO test example.

You can see the complete diff here.

The changes boil down to the following:

  • Moving all the *.c files to *.cpp and fixing various typecasting laxness that GCC 4.9.1 complains about when compiling C++
  • Creating the config.cmake file to tell cmake about the extension and its files
  • Creating the ext_boxwood.php “systemlib” file to tell HHVM about the exported files from my extension
  • Adding an explicit COMPILE_DL_BOXWOOD define to php_boxwood.cpp (the regular PHP 5 build process would have done this for me.) This is necessary to ensure the ZEND_GET_MODULE() macro gets executed, which causes necessary module metadata to be exported so that HHVM can read it.
  • Refactor module globals initialization to use the ZEND_INIT_MODULE_GLOBALS() macro instead of explicitly initializing globals in the MINIT function. This change is a good practice with standard PHP extensions as well, but it was required here to avoid a crash from a failing assertion in the HHVM version of a TSRM function.
  • Refactoring all the tests from individual .phpt files per test to separate files for each test’s sections – test, expected output, skip condition, etc.

Once I had the module compiling, though, it took me a while to get the code properly running in HHVM. In one of those “confusing at the time but obvious in retrospect” situations, the solution is that for my module (which is both dynamic and making use of the Zend Engine compatibility later, HHVM needs to be run with both the -d hhvm.enable_zend_compat=true and the DynamicExtensions.0=/path/to/ arguments for the module to be loaded and initialized. With just DynamicExtensions.0=/path/to/, the module is loaded, but not initialized properly.

Even still, I had trouble getting the built-in test runner to recognize what I thought were the right incantations for per-test-suite configuration options, so I just added my necessary options to the test runner explicitly.

Having figured out the configuration mumbo-jumbo, any future extension conversions to HHVM will go much quicker. However, given the nature of HHVM, I would be curious to see a performance comparison between an in-PHP version of this code benefitting from HHVM’s JIT compilation and the in-C version. Performance was the initial reason for writing this extension in C in the first place so it would be interesting to see if HHVM’s compilation makes that path obsolete.

Converting a PHP Extension to PHP 7

To dig under the hood of PHP 7 a bit, I decided to see how hard it would be to update my Boxwood extension to be compatible with PHP 7.

Boxwood is something I built at Ning a few years ago to do efficient multi-word replacement in text. We used it to “bleep out” naughty words that Network Creators didn’t want to see on their networks. By building a trie of all the words to replace, it’s able to do a single pass through the text that might contain naughtiness and make replacements speedily.

It’s not a terribly complicated PHP extension but it exercises a few Zend Extension API features such as function calls (obviously), parameter parsing and type checking, resources, module globals and hash table traversal.

Guided by the handy instructions at I forked ning/boxwood over to davidsklar/boxwood, created a php7 branch and got to work. You can see the complete diff here.

Total time to make all the changes was about 40 minutes, and that includes some unrelated-to-PHP-7 housekeeping to remove warnings that gcc didn’t care about when I originally released boxwood but clang/LLVM (what I’m using now) complains about.

The interesting changes are all in php_boxwood.c.

First, I had to change how the boxwood resource is handled. Boxwood uses a PHP resource to represent a collection of words to bleep. The resource is created with boxwood_new(), words get added to the resource by boxwood_add_text(), and then boxwood_replace_text() does the replacement. The resource type is now zend_resource (instead of zend_rsrc_list_entry) and there’s a new syntax for creating a resource. Additionally, to retrieve a resource from PHP’s internal resource list when it’s passed as an argument to a userspace function, I had to change to use the zend_fetch_resource() function instead of the ZEND_FETCH_RESOURCE() macro.

Next, there were some changes to string handling in function arguments and return values. Instead of receiving a string argument with s in the zend_parse_parameters() argument specifier string, I use S. (That’s a capital S instead of lowercase s.) This puts the passed in string into a zend_string structure (instead of separate variables for the character data and length). The val member of the struct has the character data.

After that, I had to update the hash traversal in boxwood_replace_text(). The code became much simpler. Instead of tracking hash position myself and using a for loop with verbose increment and condition steps, I use the dainty ZEND_HASH_FOREACH_VAL() macro which conveniently iterates for me, plopping each hash value in a zval for my use.

The other little cleanup was due to the disappearance of IS_BOOL – the one place I used that I now have to test for IS_TRUE and IS_FALSE separately.

All in all an easy adventure. Next I think I’ll see how it goes getting it to work with HHVM’s ext_zend_compat.

xsane segfault on OS X Mavericks

In attempting to use xsane with my ancient and swell CanoScan LiDE 35 on my less ancient and swell MacBook Pro running OS X Maverics, I was getting segfaults that lldb told me were happening in libcrypto:

(lldb) bt
* thread #1: tid = 0xbeb58, 0x00000001002548fd libcrypto.1.0.0.dylib`EVP_PKEY_CTX_free + 14, queue = '', stop reason = EXC_BAD_ACCESS (code=1, address=0x1000000000)
  * frame #0: 0x00000001002548fd libcrypto.1.0.0.dylib`EVP_PKEY_CTX_free + 14
    frame #1: 0x0000000100248a73 libcrypto.1.0.0.dylib`EVP_MD_CTX_cleanup + 127
    frame #2: 0x00000001001129cc libnetsnmp.25.dylib`sc_hash + 437
    frame #3: 0x0000000100110b93 libnetsnmp.25.dylib`hash_engineID + 92
    frame #4: 0x00000001001108d3 libnetsnmp.25.dylib`search_enginetime_list + 44
    frame #5: 0x0000000100110cb6 libnetsnmp.25.dylib`set_enginetime + 60
    frame #6: 0x000000010011051d libnetsnmp.25.dylib`init_snmpv3_post_config + 150
    frame #7: 0x0000000100113bbe libnetsnmp.25.dylib`snmp_call_callbacks + 480
    frame #8: 0x00000001035ddbdd`mc_network_discovery + 118
    frame #9: 0x00000001035da4b2`attach_one_config + 635
    frame #10: 0x00000001035d58aa`sanei_configure_attach + 169
    frame #11: 0x00000001035da02b`sane_magicolor_get_devices + 96
    frame #12: 0x000000010001e97d libsane.1.dylib`sane_dll_get_devices + 176
    frame #13: 0x0000000100003cbf scanimage`main + 1751
    frame #14: 0x00007fff90aac5c9 libdyld.dylib`start + 1
    frame #15: 0x00007fff90aac5c9 libdyld.dylib`start + 1

Various brew reinstall incantations and searching around for similar bugs/solutions proved unfruitful. However, grep -i snmp /usr/local/etc/sane.d/* turned up references in kodakaio.conf and magicolor.conf. Commenting out the net autodiscovery line in magicolor.conf solved the problem.

Yes, this is one of those “making a note of it so it gets indexed by a search engine and I (or others) can find it later” posts.

Dating Platform

Everyone who fancies themselves a club promoter / Yenta-in-training / Gladwellan connector should be operating their own dating app. Where is the platform for the turnkey creation of dating apps/web sites? It brings the tech, you bring the style, invites, and spark that makes the trendy bar succeed while the lame bar next door fails.

These guys have a solution for $2 (plus $150 if you don’t want to compile the source code yourself!) Anybody tried it?

David at the O'Reilly Software Architecture Conference

I’m excited to be giving a talk at the upcoming O’Reilly Software Architecture Conference this March in Boston. I’ll be speaking about “How To Talk To Non-Engineers”. Come learn how to make nice to business people, designers, product managers, and all those other alien species who seem to want the impossible!