Microsoft unleashed a blogstorm over night with the announcement that it intends to release the code for its .NET Framework Libraries under one of its shared source licenses.

Cue headlines about patent trolling and pseudo open source, and traps being set for open source developers.

While it would be easy to dismiss the response as open source paranoia, it does appear that Microsoft’s mixed messages over open source, and its use of shared source licenses, could potentially create problems for its open source interoperability partners.

First of all it’s worth stating that the license Microsoft has chosen for this project – the Microsoft Reference License – is not an open source license, and is not one of the licenses the company has proposed for adoption by the OSI.

The announcement itself also makes no reference to “open source” (not that it stopped many bloggers/commenters making the leap) so it’s a little unfair to accuse the company of deliberately misleading people.

Second, much of the reaction focuses on what the license does not allow, rather than what it does. In making the announcement Scott Guthrie, a general manager in Microsoft’s developer division, maintained that there will be benefits for .NET developers. “Having source code access and debugger integration of the .NET Framework libraries is going to be really valuable for .NET developers:

“Being able to step through and review the source should provide much better insight into how the .NET Framework libraries are implemented, and in turn enable developers to build better applications and make even better use of them,” he wrote.

The choice of MS-RL is potentially problematic for open source developers, however, particularly Microsoft’s best friend Novell.

The license allows developers to see the source code but not to modify it or make use of it in other programs. That means the code is incompatible with Novell’s Mono project, which has created an open source implementation of .NET. The patent-troll fear is that by releasing the code under MS-RL, Microsoft has set the scene for a later patent infringement claim against Mono.

Miguel de Icaza, vice president for the developer platform at Novell and founder of the Mono project, certainly warned Mono developers off taking a look at the code.

“People that are interested in continuing to contribute to Mono, or that are considering contributing to Mono’s open source implementation of those class libraries should not look at this upcoming source code release,” he wrote on his personal blog, while welcoming the move and likening it to Sun’s slow progress towards the eventually open sourcing of Java.

Even if predictions of Microsoft trap-setting are wide of the mark, it is clear to see that the company has created a dilemma for itself in wanting to engage with open source vendors on its own terms.

Clearly the company doesn’t mind that by engaging with Novell it leaves Red Hat out in the cold (and indeed that might be the point), but if it wants to provide interoperability with at least some open source players it needs to find some way around the situation where engaging with its developer ecosystem leaves its open source partners out in the cold.

As de Icaza added: “I still believe that there is a good business case for opening more stuff under the more liberal MS-PL license. And of course, beyond the Microsoft ecosystem, there is the Mono ecosystem, where we could leverage that code if it were open source.”

Does Microsoft care about the Mono ecosystem? If I were Novell, it’s the question I would be asking.