gistfile1.java

@Singleton
public class DroolsEngine implements RulesEngine {
    private static final Logger log = LoggerFactory.getLogger(DroolsEngine.class);

    private final KieServices kieServices;
    private ReleaseId currentReleaseId;
    private final KieContainer kieContainer;
    private final KieSession session;

    @Inject
    public DroolsEngine() {
        kieServices = KieServices.Factory.get();
        currentReleaseId = kieServices.newReleaseId("org.graylog2", "dynamic-rules", "1.0");

        createAndDeployJar(kieServices, currentReleaseId, "");

        kieContainer = kieServices.newKieContainer(currentReleaseId);
        session = kieContainer.newKieSession();
    }

    @Override
    public boolean addRule(String ruleSource) {
        ReleaseId newReleaseId = nextRelease(currentReleaseId);
        try {
            createAndDeployJar(kieServices, newReleaseId, ruleSource);
            currentReleaseId = newReleaseId;
        } catch (IllegalArgumentException e) {
            log.error("Could not add rule to engine, syntax errors found.");
            return false;
        }
        kieContainer.updateToVersion(newReleaseId);
        return true;
    }

    @Override
    public int evaluate(Message message) {
        session.insert(message);
        return session.fireAllRules();
    }

    private ReleaseId nextRelease(ReleaseId releaseId) {
        final List<String> versionParts = Splitter.on('.').limit(2).splitToList(releaseId.getVersion());
        int newMinor = Integer.parseInt(versionParts.get(1)) + 1;
        return kieServices.newReleaseId(releaseId.getGroupId(),
                                        releaseId.getArtifactId(),
                                        versionParts.get(0) + "." + newMinor);
    }

    private static KieModule createAndDeployJar(KieServices ks, ReleaseId releaseId, String... drls) {
        byte[] jar = createJar(ks, releaseId, drls);

        // Deploy jar into the repository
        final KieModule kieModule = deployJarIntoRepository(ks, jar);
        return kieModule;
    }

    private static byte[] createJar(KieServices ks,
                                    ReleaseId releaseId,
                                    String... drls) {
        KieFileSystem kfs = ks.newKieFileSystem()
                .generateAndWritePomXML(releaseId);
        for (int i = 0; i < drls.length; i++) {
            if (drls[i] != null) {
                kfs.write("src/main/resources/r" + i + ".drl", drls[i]);
            }
        }
        KieBuilder kb = ks.newKieBuilder(kfs).buildAll();
        final Results results = kb.getResults();
        if (results.hasMessages(Level.ERROR)) {
            log.warn("Compiling new rules failed: ", results.getMessages(Level.ERROR));
            throw new IllegalArgumentException("Rules syntax error");
        }
        InternalKieModule kieModule = (InternalKieModule) ks.getRepository().getKieModule(releaseId);

        final byte[] bytes = kieModule.getBytes();
        return bytes;
    }

    private static KieModule deployJarIntoRepository(KieServices ks, byte[] jar) {
        Resource jarRes = ks.getResources().newByteArrayResource(jar);
        return ks.getRepository().addKieModule(jarRes);
    }

gistfile2.java

    @Test
    public void addedRuleIsVisibleInSession() {
        final DroolsEngine engine = new DroolsEngine();

        String rule = "import org.graylog2.plugin.Message;\n" +
                "declare Message\n" +
                "    @role( event )\n" +
                "end\n" +
                "\n" +
                "rule \"test matcher\"\n" +
                "when\n" +
                "    $m : Message( filterOut == false )\n" + // , source == "test"
                "then\n" +
                "    modify($m) { setFilterOut(true) }\n" +
                "end\n";
        final boolean valid = engine.addRule(rule);
        assertTrue(valid, "Rule should compile without errors");

        final int rulesFired = engine.evaluate(new Message("test message", "test", DateTime.now()));
        assertEquals(rulesFired, 1, "rule should have matched");
    }

gistfile3.txt

java.lang.NullPointerException
	at java.io.FilterOutputStream.write(FilterOutputStream.java:97)
	at org.drools.compiler.compiler.io.memory.MemoryFileSystem.writeJarEntries(MemoryFileSystem.java:437)
	at org.drools.compiler.compiler.io.memory.MemoryFileSystem.writeJarEntries(MemoryFileSystem.java:430)
	at org.drools.compiler.compiler.io.memory.MemoryFileSystem.writeJarEntries(MemoryFileSystem.java:430)
	at org.drools.compiler.compiler.io.memory.MemoryFileSystem.writeJarEntries(MemoryFileSystem.java:430)
	at org.drools.compiler.compiler.io.memory.MemoryFileSystem.zip(MemoryFileSystem.java:387)
	at org.drools.compiler.compiler.io.memory.MemoryFileSystem.writeAsBytes(MemoryFileSystem.java:365)
	at org.drools.compiler.kie.builder.impl.MemoryKieModule.getBytes(MemoryKieModule.java:64)
	at org.graylog2.rules.DroolsEngine.createJar(DroolsEngine.java:122)
	at org.graylog2.rules.DroolsEngine.createAndDeployJar(DroolsEngine.java:96)
	at org.graylog2.rules.DroolsEngine.addRule(DroolsEngine.java:66)
	at org.graylog2.rules.DroolsEngineTest.addedRuleIsVisibleInSession(DroolsEngineTest.java:37)