Add Extender that allows bundles to declare a transformer resource

bundles/org.eclipse.equinox.transforms.hook/src/org/eclipse/equinox/internal/transforms/TransformerBundleExtender.java

@@ -0,0 +1,89 @@
+/*******************************************************************************
+ * Copyright (c) 2024 Christoph Läubrich and others.
+ *
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License 2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Christoph Läubrich - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.equinox.internal.transforms;
+
+import java.net.URL;
+import java.util.Dictionary;
+import java.util.Map;
+import org.osgi.framework.*;
+import org.osgi.util.tracker.BundleTracker;
+import org.osgi.util.tracker.BundleTrackerCustomizer;
+
+/**
+ * Extender that scans for bundle header {@value #EQUINOX_TRANSFORMER_HEADER}
+ * that declare a bundle wants to transform resources. The header can be either
+ * a resource in the bundle (e.g. <code>/transform.csv</code>) in which case it
+ * is assumed to use the default replace transformer, or can specify a
+ * transformation type e.g. <code>xslt;/transform.csv</code>
+ */
+class TransformerBundleExtender implements BundleTrackerCustomizer<ServiceRegistration<URL>> {
+
+	private static final String EQUINOX_TRANSFORMER_HEADER = "Equinox-Transformer"; //$NON-NLS-1$
+	private BundleContext bundleContext;
+
+	public TransformerBundleExtender(BundleContext bundleContext) {
+		this.bundleContext = bundleContext;
+	}
+
+	@Override
+	public ServiceRegistration<URL> addingBundle(Bundle bundle, BundleEvent event) {
+		TransformerInfo info = getTransformerInfo(bundle);
+		if (info != null) {
+			return bundleContext.registerService(URL.class, info.url(),
+					FrameworkUtil.asDictionary(Map.of(TransformTuple.TRANSFORMER_TYPE, info.type())));
+		}
+		return null;
+	}
+
+	@Override
+	public void modifiedBundle(Bundle bundle, BundleEvent event, ServiceRegistration<URL> registration) {
+		// state modifications are not relevant here
+	}
+
+	@Override
+	public void removedBundle(Bundle bundle, BundleEvent event, ServiceRegistration<URL> registration) {
+		registration.unregister();
+	}
+
+	private static TransformerInfo getTransformerInfo(Bundle bundle) {
+		Dictionary<String, String> headers = bundle.getHeaders(""); //$NON-NLS-1$
+		String header = headers.get(EQUINOX_TRANSFORMER_HEADER);
+		if (header != null && !header.isBlank()) {
+			String[] split = header.split(";", 2); //$NON-NLS-1$
+			if (split.length == 2) {
+				URL entry = bundle.getEntry(split[1]);
+				if (entry != null) {
+					return new TransformerInfo(split[0], entry);
+				}
+			} else {
+				URL entry = bundle.getEntry(header);
+				if (entry != null) {
+					return new TransformerInfo(ReplaceTransformer.TYPE, entry);
+				}
+			}
+		}
+		return null;
+	}
+
+	private static record TransformerInfo(String type, URL url) {
+
+	}
+
+	static void start(BundleContext bundleContext) {
+		BundleTracker<ServiceRegistration<URL>> tracker = new BundleTracker<>(bundleContext,
+				Bundle.RESOLVED | Bundle.ACTIVE | Bundle.STARTING, new TransformerBundleExtender(bundleContext));
+		tracker.open();
+	}
+
+}

bundles/org.eclipse.equinox.transforms.hook/src/org/eclipse/equinox/internal/transforms/TransformerHook.java

@@ -47,6 +47,7 @@ public void addHooks(HookRegistry hookRegistry) {
 	public void start(BundleContext context) throws BundleException {
 		try {
 			ReplaceTransformer.register(context, this);
+			TransformerBundleExtender.start(context);
 			this.transformers = new TransformerList(context, logServices);
 		} catch (InvalidSyntaxException e) {
 			throw new BundleException("Problem registering service tracker: transformers", e); //$NON-NLS-1$