How does one enforce aspects of a license?

Question

I've been provided a SourceMod plugin for a community game server. I was provided the compiled plugin, but not the source code. The license and explanation provided describes all SourceMod plugins as derivatives, meaning I should also receive a copy of the source.

How does one enforce such a requirement?

To be clearer, this is not about the SourceMod source code. That is available at the links I provided. This is about source code from the derived plugins made by a third party. The plugin is not listed on the SourceMod page, thus the source code is not available via their forums.

Answer 1

Enforcing any restrictions imposed is difficult, and ultimately you may have to bring it to legal proceedings.

The first step for any project, yours or someone else's, is to notify: if you spot something that doesn't comply, you should notify the project's author. They can deal with their own restrictions - you don't know if they've made an exception for this case or not. If you're the owner, your job is to notify the non-compliant: a polite email, simply saying you've noticed they don't do X and would they please do so, will suffice.

If you need to take it on further, there are various legal proceedings. Ultimately, the courts have your back because it's your work and someone is using it in a way they aren't permitted to. You may also be able to issue a DMCA takedown request, which is a legally-backed way of telling someone to remove something you don't want there. Assuming you have permission to do so.

Answer 2

Generally, in order to pursue legal action against someone, you need to have standing — that is, be a directly involved party. While there might be some legal theories that users of GPL-licensed software are intended beneficiaries of the license and therefore could make a case, I'm not aware of this ever having been tested anywhere. Lawsuits like those brought by gpl-violations.org work because they directly involved a copyright holder — one of the people who granted use to their code via the GPL.

I'm not a lawyer, but you don't have to take my word for it; here is Eben Moglen writing for the Free Software Foundation:

[...] despite the broad right of distribution conveyed by the GPL, enforcement of copyright is generally not possible for distributors: only the copyright holder or someone having assignment of the copyright can enforce the license.

Here, "distribution" is just one of the freedoms granted by the GPL, but the same basic concept applies to the others as well.

So that means that in this case, your best course of action is to contact the SourceMod authors and make them aware of the violation, and ask them to ask the module authors to comply.

Answer 3

Enforcement is difficult.

First step would be to politely ask. The last step would be to bring it to court. The difficulty is to chose wisely the escalation steps in between and to decide when to stop.