PHP Internals News: Episode 52: Floats and Locales – Derick Rethans

PHP Internals News: Episode 52: Floats and Locales

In this episode of “PHP Internals News” I talk with George Banyard (Website, Twitter, GitHub, GitLab) about an RFC that he has proposed together with Máté Kocsis (Twitter, GitHub, LinkedIn) to make PHP’s float to string logic no longer use locales.

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Derick Rethans 0:16

Hi, I’m Derick. And this is PHP internals news, a weekly podcast dedicated to demystifying the development of the PHP language. This is Episode 52. Today I’m talking with George Banyard about an RFC that he’s made together with Mate Kocsis. This RFC is titled locale independent floats to string. Hello, George, would you please introduce yourself?

George Banyard 0:39

Hello, I’m George Peter Banyard. I’m a student at Imperial College and I work on PHP in my free time.

Derick Rethans 0:47

All right, so we’re talking about local independent floats. What is the problem here?

George Banyard 0:52

Currently when you do a float to string conversion, so all casting or displaying a float, the conversion will depend on like the current local. So instead of always using like the decimal dot separator. For example, if you have like a German or the French locale enabled, it will use like a comma to separate like the decimals.

Derick Rethans 1:14

Okay, I can understand that that could be a bit confusing. What are these locales exactly?

George Banyard 1:20

So locales, which are more or less C locales, which PHP exposes to user land is a way how to change a bunch of rules on how string and like stuff gets displayed on the C level. One of the issues with it is that like it’s global. For example, if you use like a thread safe API, if you use the thread safe PHP version, then set_locale() is not thread safe, so we’ll just like impact other threads where you’re using it.

Derick Rethans 1:50

So a locale is a set of rules to format specific things with floating point numbers being one of them in which situations does the locale influence the display a floating point numbers in every situation in PHP or only in some?

George Banyard 2:06

Yes, it only impacts like certain aspects, which is quite surprising. So a string cast will affect it the strval() function, vardump(), and debug_zval_dump() will all affect the decimal locator and also printf() with the percentage lowercase F, but that’s expected because it’s locale aware compared to the capital F modifier.

Derick Rethans 2:32

But it doesn’t, for example, have the same problem in the serialised function or say var_export().

George Banyard 2:37

Yeah, and json_encode() also doesn’t do that. PDO has special code which handles also this so that like all the PDO drivers get like a constant treat like float string, because that could like impact on the databases.

Derick Rethans 2:53

How is it a problem that with some locales enabled and then uses a comma instead of the decimal point. How can this cause bugs and PHP applications?

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Xdebug Update: April 2020 – Derick Rethans

Xdebug Update: April 2020

Another monthly update where I explain what happened with Xdebug development in this past month. These will be published on the first Tuesday after the 5th of each month. Patreon supporters will get it earlier, on the first of each month. You can become a patron to support my work on Xdebug. If you are leading a team or company, then it is also possible to support Xdebug through a subscription.

In March, I worked on Xdebug for about 60 hours, on the following things:

Xdebug 2.9.5

The 2.9.5 release addresses a few bugs. One of them was a follow on from the issue where Xdebug would crash when another extension would run code in PHP’s Request Init stage, but only on a second or later request in the same PHP process. As this is not something that’s easy to catch with PHP’s testing framework that Xdebug uses, this issue slipped through the cracks.

The release fixes another bug, where throwing an exception from within a destructor would crash Xdebug. The fix for this was merely making sure that PHP’s internal state is still available:

- if (!(ZEND_CALL_INFO(EG(current_execute_data)) & ZEND_CALL_HAS_SYMBOL_TABLE)) {
+ if (EG(current_execute_data) && !(ZEND_CALL_INFO(EG(current_execute_data)) & ZEND_CALL_HAS_SYMBOL_TABLE)) { 

Beyond these two crashes, the release also addressed an issue where Xdebug did not always correct catch where executable code could exist for code coverage analyses. Over the last decade, PHP has been getting more and more optimised, with more internal engine instructions. Unfortunately that sometimes means that these are not hooked into by Xdebug, to see whether there could be a line of code that would make use of these opcodes. As this is often very dependent on how developers lay out their code, these issues are often found by them. Luckily, these issues are trivially fixed, as long as I have access to just the file containing that code. I then analyse it with vld to see which opcode (PHP engine instruction) I have missed.

Xdebug 3 and Xdebug Cloud

Most of my time was spend on getting Xdebug Cloud to a state where I can invite select developers to alpha test it. This includes allowing for Xdebug to connect to Xdebug Cloud. There is currently a branch available, but it still lacks the addition of SSL encryption, which is a requirement for allowing safe transport of debug information.

The communications between an IDE and Xdebug through Xdebug Cloud is working, with a few things related to detecting disconnections more reliably still outstanding.

As Xdebug Cloud needs integration in debugging clients (such as PhpStorm, and other IDEs), I have been extending the dbgpProxy tool to act as intermediate link between existing IDEs and Xdebug Cloud without IDEs having to change anything. This work is still ongoing, and is not documented yet, but I hope to finish that in the next week. Once that and SSL support in the Xdebug to Xdebug Cloud communication has been finalized, I will reach out to subscribers of the Xdebug Cloud newsletter to see if anybody is interested in trying it out.


The PHP Internals News continues its second season. Episodes in the last month included a discussion on PHP 8’s JIT engine and increasing complexity,

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