FELIX-6759 - PROTOTYPE: use plurl for URL handler factory multiplexing

framework/src/main/java/org/apache/felix/framework/PlurlURLHandlers.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.felix.framework;
+
+import java.io.IOException;
+import java.net.ContentHandler;
+import java.net.URLStreamHandler;
+
+import org.apache.felix.framework.plurl.Plurl;
+import org.apache.felix.framework.plurl.PlurlContentHandlerFactory;
+import org.apache.felix.framework.plurl.PlurlStreamHandlerFactory;
+
+/**
+ * <p>
+ * PROTOTYPE (FELIX-6759): adapts Felix' {@link URLHandlers} onto the plurl
+ * multiplexing URL factories.
+ * </p>
+ * <p>
+ * {@code URLHandlers} currently claims the JVM-wide {@code java.net.URL} stream
+ * handler factory by reflectively swapping a private static field
+ * ({@code SecureAction.swapStaticFieldIfNotClass}). Obtaining a
+ * {@code MethodHandles.Lookup} trusted enough to do that is the sole reason the
+ * framework still uses {@code sun.misc.Unsafe}, and it means whichever framework
+ * installs itself last wins the singleton - so Felix and Equinox cannot coexist in
+ * one JVM without clobbering each other.
+ * </p>
+ * <p>
+ * Plurl instead installs one cooperative router through the supported
+ * {@code URL.setURLStreamHandlerFactory} API and lets any number of parties
+ * register with it. Each registered factory answers {@link #shouldHandle(Class)}
+ * to say whether a given calling class belongs to it; plurl walks the call stack
+ * and routes accordingly. That maps directly onto what
+ * {@link URLHandlers#getFrameworkFromContext()} already does.
+ * </p>
+ * <p>
+ * See {@code org/apache/felix/framework/plurl/README.md} for the provenance of the
+ * vendored plurl sources and the <b>unresolved licensing question</b> that currently
+ * blocks this approach.
+ * </p>
+ */
+class PlurlURLHandlers implements PlurlStreamHandlerFactory, PlurlContentHandlerFactory
+{
+    private final URLHandlers m_delegate;
+
+    PlurlURLHandlers(URLHandlers delegate)
+    {
+        m_delegate = delegate;
+    }
+
+    /**
+     * Registers this framework's handlers with the plurl router, installing the
+     * router first if nobody has yet.
+     */
+    static PlurlURLHandlers install(URLHandlers delegate) throws IOException
+    {
+        PlurlURLHandlers handlers = new PlurlURLHandlers(delegate);
+        Plurl.add((PlurlStreamHandlerFactory) handlers);
+        Plurl.add((PlurlContentHandlerFactory) handlers);
+        return handlers;
+    }
+
+    /**
+     * Unregisters this framework's handlers, leaving the router in place for any
+     * other framework instance still using it.
+     */
+    void uninstall() throws IOException
+    {
+        Plurl.remove((PlurlStreamHandlerFactory) this);
+        Plurl.remove((PlurlContentHandlerFactory) this);
+    }
+
+    /**
+     * Tells plurl whether the given calling class belongs to this framework.
+     * <p>
+     * This replaces the call stack walking URLHandlers does today: rather than
+     * inspecting the stack itself to work out which framework owns the caller, the
+     * router asks each registered factory about a single candidate class.
+     */
+    @Override
+    public boolean shouldHandle(Class<?> clazz)
+    {
+        if (clazz == null)
+        {
+            return false;
+        }
+        ClassLoader loader = clazz.getClassLoader();
+        if (loader == null)
+        {
+            return false;
+        }
+        String name = loader.getClass().getName();
+        return name.startsWith("org.apache.felix.framework.BundleWiringImpl$BundleClassLoader")
+            || name.startsWith("org.apache.felix.framework.ModuleImpl$ModuleClassLoader")
+            || name.equals("org.apache.felix.framework.searchpolicy.ContentClassLoader");
+    }
+
+    @Override
+    public URLStreamHandler createURLStreamHandler(String protocol)
+    {
+        return m_delegate.createURLStreamHandler(protocol);
+    }
+
+    @Override
+    public ContentHandler createContentHandler(String mimeType)
+    {
+        return m_delegate.createContentHandler(mimeType);
+    }
+}