db4o-7.4 - as needed by Freenet's plugin-WebOfTrust and plugin-Freetalk

This repository contains version 7.4.63.11890 of db4o as it was shipped by Freenet's contrib repository, aka "freenet-ext.jar", as of tag v29.

freenet-ext.jar used to be a monolithic JAR intended to ship all of Freenet's dependencies. As Freenet is nowadays capable of shipping individual JARs freenet-ext.jar is going away.
As a consequence db4o is being moved into this repository so it can be directly compiled into WebOfTrust and Freetalk.

This is NOT the latest version of db4o!
Instead it is what has been deployed at Freenet from at least 2011 to 2018 and what has proven to work well with WebOfTrust and Freetalk. Later versions of db4o have been tried but caused severe bugs which must first be fixed before we upgrade.

NOTICE: This doesn't include the commit history of db4o as it is not based on an official db4o repository and thus should not be propagated on the Internet beyond Freenet usage!
This is because to ensure the code is the very same version as what has proven to work well with Freenet it is a fork of Freenet's contrib repository with anything besides db4o removed. This may or may not be equal to what db4o has once shipped officially.

Building

In order to ease validating that this produces a build which is identical to what was shipped with freenet-ext this does not use Gradle yet but ships the same Ant builder as used by freenet-ext.
Thus you can build using:

ant clean
ant jar

As of tag v31 of this repository and tag v29 of contrib it has been manually validated that the db4o class files as built and JAR'ed by this repository are binary equal to the ones built and JAR'ed by contrib.

Build output

• db4o.jar: The main output.
• build/: Classes of db4o.jar
• build-db4oj/: Db4o main classes without optimizations. These are copied into the build/ directory by the build script.
• build-db4ojdk*/: Optimizations. The JDK version in their name is the minimum Java version required for each. They are copied into the build/ directory by the build script.

TODOs

• While the unit test files are present they are currently ignored by the Ant builder.
  This is because whoever committed db4o to the repository did not include db4o's "db4ounit" library which is needed for the tests.
  The code of it should be added to this repository and the Ant builder should be amended to run the unit tests.
  However this should IMHO be postponed until after the initial release of Freenet without contrib / of WoT with bundled db4o:
  There likely is a reason that whoever added db4o to contrib left out the tests, and that reason may be that they fail frequently. The complex procedure of getting rid of contrib at Freenet should not unnecessarily be complicated by introducing fragile tests here.