A commonly held view is that this is possible if, and only if, - they integrate using web services, and not direct invocations: it's commonly known as the "web services loophole". I don't agree with the FSF's interpretation that invoking independent PHP scripts constitutes linking, but that appears to be their stance. - the GPL is version 2, not 3 (to be clarified for GPL3: there was discussion about closing that loophole during the GPL3 design) ---- Original Message ---- From: jeff@viapositiva.net To: development@drupal.org Subject: RE: [development] Modules that integrate non-GPL PHP apps violate theGPL. Date: Thu, 30 Aug 2007 02:08:56 -0500

For quite some time, it has been commonly understood in the Drupal community that non-GPL software (like a third-party PHP message board

system) can be integrated into Drupal legally by using an intermediary 'bridge' module. After some in-depth emails with the Free Software foundation's license gurus, it's become clear that this

is NOT the case.

Before going any further, I want to make clear that I'm not expressing approval or disapproval of this: I'm just relaying the conclusions that were reached after several days of discussion and questioning with the FSF.

Why do these modules violate the GPL?

1) Under the FSF's accepted interpretation of the GPL, if a module is

integrating Drupal and another PHP script, by calling one's APIs when

triggered by the other for example, its purpose is to make a single unit of software out of those parts.

2) If multiple programs are operating together and functioning as one

unit, all the pieces must be GPL'd.

There are a lot of angles to approach the question from, but that's what it boils down to. From a developer's perspective, if debug_backtrace() can ever include functions from both Drupal and an

external program, you've turned them into a single program.

There are some potential solutions, though none of them are ideal.

1) Add a notice to Drupal's license that clarifies that writing such

modules IS explicitly allowed. This is problematic, however, because

that would make Drupal non-GPL'd itself, a GPL variant, and we would

require explicit relicensing permission by the authors of any GPL code we wish to include.

2) Remove modules that integrate with third-party non-GPL code from the CVS repository, even if they do not *include* the aforementioned

non-GPL code.

3) Continue on as we are, and don't try to police these issues as there are NOT likely to be any real complaints. (No one that I know of is trying to SELL modules that integrate with non-GPL resources, for example.)

This is an important question for us, and other GPL'd projects, to work through. Many GPL CMS's rely on integration components for critical functionality (message boards and mass mailing are two common examples). I can provide some detailed snippets from the correspondence to those who want them, but I'm not sure it would be useful for me to spend any more time corresponding. I exhausted my list of questions, and I'm just summarizing what I found out.

--Jeff