Wednesday, August 5, 2015

SQL Relay License Update


SQL Relay is made up of a bunch of different parts: the server, the command line clients, API's for various languages, tests, documentation, etc. The server and command line clients have always been licensed under the GPL. The API's have been licensed under various licenses, as appropriate to each API - LGPL, Artistic License, Creative Commons, etc.

In the late 90's, when I first decided to use the GPL for the server, the open source community seemed to interpret the GPL as allowing dynamic linking of non-GPL-compatible libraries/plugins/modules/drivers into GPL-licensed programs. The Linux kernel was the poster boy for this interpretation, as hardware vendors provided (and still provide) closed-source drivers, under various non-GPL-compatible licenses. In the database arena, GPL-licensed programs like sqsh and tora illustrated this same interpretation.

The rationale seemed to be that the GPL-licensed program included instructions for loading and interfacing with a non-GPL library, but not the library itself. Headers generally "didn't count" so presumably neither did whatever bits of the library the linker needed to examine.

The GPL-licensed program and non-GPL library/plugin/module/driver were considered separate. They were only combined to create a derivative work at runtime. Copies of the pages of memory that composed that work could not be lawfully distributed, but distribution as separate components was fine.

That seemed to be conventional wisdom at the time.

I wasn't totally ambivalent to the politics associated with the GPL, but really, I needed to choose a license, the GPL was popular, and seemed to fit.

Since then, debates have raged. GNU has made their position abundantly clear: programs that are capable of sharing the same address space with a library/module/plugin/driver are a derivative work of the two, retroactively. Community opinion seems to be divided. The Linux development community is said to have a "gentlemen's agreement" with hardware manufacturers, but nothing in writing. There have been a few court cases and they've gone both ways.

These developments put projects like SQL Relay in an interesting position. Obviously it is the intention of the authors to allow linking with various non-GPL-compatible libraries, but under modern interpretation, the license doesn't explicitly allow that.

As of the next release, 0.61, it will.

The License Exception

For cases like this, GNU recommends a "license exception". The SQLRelay Server, as defined in the file COPYING, at the root of the source distribution, will carry the following exception:

Linking The SQLRelay Server statically or dynamically with other modules is
making a combined work based on The SQLRelay Server. Thus, the terms and
conditions of the GNU General Public License cover the whole combination.

In addition, as a special exception, the copyright holders of The SQLRelay
Server give you permission to combine The SQLRelay Server with free software
programs or libraries that are released under the GNU LGPL and with code
included in the standard release of the following libraries (or modified
versions of such code, with unchanged license):

* OpenSSL and its dependencies.
* Perl-Compatible Regular Expressions (PCRE) and its dependencies.
* IBM DB2 database client libraries and their dependencies.
* Firebird database client libraries and their dependencies.
* FreeTDS client libraries and their dependencies.
* MDB Tools client libraries and their dependencies.
* MySQL database client libraries and their dependencies.
* ODBC client libraries and their dependencies.
* Oracle database client libraries and their dependencies.
* PostgreSQL database client libraries and their dependencies.
* SQLite client libraries and their dependencies.
* Sybase/SAP client libraries and their dependencies.
* Any other programs or libraries as designated, in writing, now or in the
  future, by David Muse, his authorized agents, authorized heirs, or authorized
  agents of his authorized heirs.

You may copy and distribute such a system following the terms of the GNU GPL
for The SQLRelay Server and the licenses of the other code concerned{, provided
that you include the source code of that other code when and as the GNU GPL
requires distribution of source code}.

Note that people who make modified versions of The SQLRelay Server are not
obligated to grant this special exception for their modified versions; it is
their choice whether to do so. The GNU General Public License gives permission
to release a modified version without this exception; this exception also makes
it possible to release a modified version which carries forward this exception. 

Some of the named libraries are either LGPL already or otherwise GPL-compatible, but they are listed in case that changes in the future. If I missed something, the "Any other programs or libraries..." clause makes it possible to add whatever I missed too.

The big surprise: OpenSSL. Apparently it's licensed in a way that makes it non-GPL-compatible. Who knew? Apparently the authors of wget did. Did anyone else?


In addition to making it clear that those specific libraries are OK, there is another motivation to the license update.

SQL Relay has several module frameworks. You can do all kinds of things with modules - logging, password encryption, alternative authentication mechanisms, query filtering, query translation, result set translation, and more... And additional frameworks are planned.

Without the license update, module development is sketchy. For example:

Can I write a connection module for Informix? Good question.

OpenLDAP has an odd license, is it legal to develop an OpenLDAP authentication module? Who knows?

Can a software development firm write a module for a client that interfaces with some system that the client already uses via a non-GPL-compatible library? Maybe.

Can a software vendor write a module to interface with some proprietary system they developed? Also hard to say.

What about me, personally? Can I, personally, write proprietary plugins? As the primary copyright holder, I'd think so. But can I really?

The "Any other programs or libraries..." clause in the license update provides a path to these kinds of things. New libraries can be approved. If in doubt, just ask and get a definitive answer, in writing.

As a guideline, the answer will almost certainly be yes for "client libraries" and their dependencies. By client libraries, I mean, there's some system running in its own address space and there's a library who's primary function is to provide access to it. That library is a "client library."

For other libraries, it would depend on the details.


By what authority do I change the license?

Mostly my own, partly that of the open source community, and partly that which was granted by other contributors.

I am the primary copyright holder for The SQLRelay Server. I'm not exactly sure what percentage of it I either wrote or own, but I'd bet that it's over 99%. The API's were largely contributed, but they're not affected by this change.

Over the years, patches from various contributors were applied to The SQLRelay Server, but the vast majority were "trivial bugfixes." While important, they were short and didn't demonstrate novel insight. I.e. the patch affected fewer than ten lines, the bug was easy to find, the bug is obvious now that it's been pointed out, and the fix couldn't have been implemented much differently. If the patch was short and met 2 out of 3 of the other criteria, then I deemed it trivial. Trivial bugfixes are likely not subject to copyright. This analysis and action seem consistent with those of the open source community in license update scenarios.

Some non-trivial patches were also integrated. But, I was able to get approval from the current copyright holders to make the license change. For good measure, I also got approval from all the trivial bugfixers that I could get a hold of too.

I did some contract jobs to integrate non-trivial patches against older versions into the then-current version of SQL Relay, but the language of the contract entitled me to the results.

There were also a few non-trivial patches that were once integrated into The SQLRelay Server, but have since been completely removed.

If anyone that I haven't received approval from can demonstrate that they contributed non-trivial code to The SQLRelay Server, a derivative of which still exists in the current version, and disagrees with the license change, please contact me at and we'll work something out.


So, what does the license change mean to you?

Most likely nothing at all. The license is likely now just more consistent with what you assumed already. The GPL, in general, still applies. It is just definitively legal to use SQL Relay as it was intended.

The only practical difference is that if you want to write a module that integrates with some other system via a non-GPL-compatible client library, then it is very likely possible to do so.

"But this license change undermines the purpose of the GPL!"

Perhaps. SQL Relay was not written to crusade for the GPL. I don't intend to undermine the GPL though. In fact, rather than argue over how to interpret the GPL, I'm doing this in deference to GNU, who recommend exactly this action.

The GPL is great. Free software wouldn't be where it is without the GPL. With this update, it's still a good fit for this project.