RFC 34: License Policy Enforcement
Authors: Frank Warmerdam
This document proposes the addition of a new mechanisms so that applications and end users can define a license policy, and so that GDAL can help avoid license conflicts between proprietary and reciprocally licensed applications and format drivers.
Reciprocal FOSS License: A open source software license, such as the GPL, that requires all other software components linked into the same executable and distributed beyond the creator to also be offered under open source terms.
Non-Reciprocal FOSS License: A open source software license, such as MIT, BSD or LGPL, that does not place any requirements on other linked components in the same executable at distribution time.
Proprietary License: Software provided under terms that do not adhere to the requirements of the open source definition, such as libraries from Oracle (OCI), Lizardtech (MrSID) and Erdas (ECW). While often offered for zero cost, these components are incompatible with reciprocal FOSS licenses and may place a variety of other restrictions on the distributor or end user.
GDAL/OGR is distributed under the Non-Reciprocal MIT open source license which facilitates it's use by proprietary and open source applications, and facilitates the inclusion of proprietary format drivers along side the open source format drivers. However, it is still a license violation to distribute reciprocally licensed applications (like QGIS and GRASS) which use GDAL with proprietary licensed drivers (such as the MrSID, ECW or Oracle drivers). Likewise, it is a license violation to distribute proprietary applications with reciprocally licensed drivers such as the GDAL GRASS driver, or the PDF driver.
This RFC, and the improvements it promotes are intended to facilitate users, applications and drivers setting and following license policies to avoid unintentional license violations. One area this can be particularly helpful is broad software distributions like OSGeo4W.
The general approach proposed is that drivers will declare their license category, and applications or end users will declare a policy for what sorts of drivers may be used in combination with them. The GDALDriverManager and OGRDriverRegistrar classes will apply this information to avoid unintentional license violations.
Drivers will declare one of these three driver specific licensing policies via the "LICENSE_POLICY" (DMD_LICENSE_POLICY) metadata item on the driver:
"RECIPROCAL": the driver is available under a reciprocal FOSS license such as the GPL, and should not be mixed with proprietary drivers or applications.
"NONRECIPROCAL": the driver is available under a non-reciprocal FOSS license such as MIT, or LGPL. This is the default if no licensing policy is declared and is the natural policy of drivers provided as part of GDAL without outside dependencies.
"PROPRIETARY": the driver, usually due to use of proprietary libraries, has some licensing restrictions which make it ineligible for distribution with reciprocally licensed software. This would include MrSID, ECW, and Oracle related drivers.
Application License Policy
Applications are encouraged to set one of the following licensing policies reflective of the applications nature. The policy should be set as the value of the GDAL_APPLICATION_LICENSE_POLICY configuration variable, typically via a call to GDALSetConfigOption() before the call to GDALAllRegister() or OGRRegisterAll().
"RECIPROCAL": the application is licensed under a reciprocal license such as the GPL, and no proprietary drivers should be loaded.
"PROPRIETARY": the application has some licensing restrictions which make it ineligible for distribution with reciprocally licensed software. Care will be taken to avoid loading reciprocally licensed drivers, such as the GRASS and PDF drivers.
"DEFAULT": the application does not apply any licensing restrictions. This is typical of non-GPL open source applications such as MapServer, and will be the default policy if nothing is declared.
User License Policy
The restrictions on mixing proprietary and reciprocally licensed software generally applies at the point of distribution. In particular, it is not intended to prevent the end user from assembling a variety of components for their own use as they see fit, for their own use. To that end it is important to provide a mechanism for the end user to deliberately override the restrictions on mixing reciprocally licensed, and proprietary components. This is accomplished via the GDAL_LICENSE_POLICY configuration variable which might typically be set via the environment or via the --config commandline switch to most GDAL applications. It may have the following values:
"USE_ALL": do not discard any drivers based on licensing restrictions.
"PREFER_PROPRIETARY": If there is a conflict between proprietary and reciprocally licensed drivers, use the proprietary ones.
"PREFER_RECIPROCAL": If there is a conflict between proprietary and reciprocally licensed drivers, use the reciprocally licensed ones.
In addition to setting this via config variables, there will also be a configure / nmake.opt declaration to alter the default GDAL_LICENSE_POLICY. Thus a local build could be configured to USE_ALL at build time instead of having to set environment variables or commandline switches. This would not be suitable for software that will be redistributed.
If the user selected a GDAL_LICENSE_POLICY of "USE_ALL" then no drivers are unloaded on the basis of licensing.
If the user selected a GDAL_LICENSE_POLICY of "PREFER_PROPRIETARY" or "PREFER_RECIPROCAL" then ignore the GDAL_APPLICATION_LICENSE_POLICY.
if the application select a GDAL_APPLICATION_LICENSE_POLICY of "PROPRIETARY" or "RECIPROCAL" then use that.
In the absence of a user or application level policy, default to a policy of "PREFER_PROPRIETARY".
The policy will be applied in the GDALDriverManager::AutoSkipDrivers() method and in the newly introduced OGRSFDriverManager::AutoSkipDrivers() method. The AutoSkipDrivers() method is already used to unload drivers based on GDAL_SKIP (and soon OGR_SKIP) and is generally called after the preliminary registration of drivers.
I believe the following drivers should be marked as "PROPRIETARY":
ArcSDE (raster and vector)
I believe the following drivers should be marked as "RECIPROCAL":
grass (raster and vector)
MySQL (depending on active license terms!)
The OGR SOSI driver should probably be marked as proprietary currently as it relies on linking with binary objects with unknown licencing terms, even if apparently the ultimate goal seems to open source them.
I'm a bit confused by MSG -- Meteosat Second Generation. Seems that it relies on third party stuff with both proprietary and GPL code.
I am unsure about the ODBC based drivers. I suppose PGEO and MSSQLSPATIAL drivers ought to be marked proprietary too? Might it depend on the actual license terms of the odbc library?
Please let me know of other drivers needing marking.
Some (all?) swig bindings automatically call GDALAllRegister() and/or OGRRegisterAll() at the point the bindings are loaded making it hard to set the application level GDAL_LICENSE_POLICY in a script before the registration takes place. To address that I believe we should expose the AutoSkipDrivers() methods via SWIG so that scripts can set the policy and then "clean" the drivers based on the policy in force.
How to test?
How to document?
Frank Warmerdam will do the core implementation in trunk. Driver maintainers may need to update the metadata for particular drivers.