jSML license is the LGPL 2.1 or a later version based on the source code notices:
jSML is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 2.1 of the License, or
(at your option) any later version.
The underlying question that was not asked directly is this:
What is the impact and obligations attached to including a modified LGPL-licensed library in a proprietary product?
Beside the standard LGPL obligations of providing credits, license text, redistributing the source code, "re-buildability" when static linking is used, there are extra requirements related to modifications in particular Section 2. provides details for this case:
- You may modify your copy or copies of the Library or any portion of it, thus forming a work based on the Library, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions [...]
This is not entirely clear to me. Why is it not clear? because is it the new modified library that becomes a "work based on the Library" or is it the whole software system that uses the modified library that becomes a "work based on the Library"? In this later case, then eventually the LGPL copyleft could be interpreted to apply to the whole software using the library.
In particular Section 2.c would apply and might be problematic for a proprietary or commercial usage:
c) You must cause the whole of the work to be licensed at no charge to all third parties under the terms of this License.
The rest of section 2. goes on to further elaborate on the topic of "based on the library" and what it means:
[...] But when you distribute the same sections as part of a whole which is a work based on the Library, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it. [...]
The net effect is that the copyleft of the LGPL 2.1 may be quite far reaching when the library is modified.
Therefore, I would seek legal advice to confirm this.
That said, another avenue could in this case to contribute your changes upstream such that they are incorporated in the jSML library. If this happens I could then use the library unmodified with relaxed requirements.
Now the entity that authored jSML seems to also provide commercial licensing and it may not be in their best business interest to incorporate such changes (but this is just speculation on my part).