Add Native#getNativeLibrary to get access to library wrapped by Native#load or Native#register

CHANGES.md

@@ -11,6 +11,7 @@ Features
 * [#1593](https://github.com/java-native-access/jna/pull/1593): Add support for DragonFly BSD x86-64 - [@liweitianux](https://github.com/liweitianux).
 * [#1595](https://github.com/java-native-access/jna/pull/1595): Add `IsProcessorFeaturePresent` to `c.s.j.p.win32.Kernel32` - [@dbwiddis](https://github.com/dbwiddis).
 * [#1602](https://github.com/java-native-access/jna/pull/1602): Add `XMoveWindow`, `XResizeWindow`, `XMoveResizeWindow`, `XRaiseWindow`, `XLowerWindow` X11 calls to `c.s.j.p.unix.X11` - [@vinceh121](https://github.com/vinceh121).
+* [#1613](https://github.com/java-native-access/jna/issues/1613): Added static helper method `Native#getNativeLibrary' for getting the underlying NativeLibrary instance from a Library interface instance or from a "registered" class - [@matthiasblaesing](https://github.com/matthiasblaesing).
 
 Bug Fixes
 ---------

src/com/sun/jna/Native.java

@@ -1918,6 +1918,52 @@ public static void register(Class<?> cls, NativeLibrary lib) {
         }
     }
 
+    /**
+     * Get the {@link NativeLibrary} instance that is wrapped by the given
+     * {@link Library} interface instance.
+     *
+     * @param library the {@link Library} interface instance, which was created
+     * by the {@link Native#load Native.load()} method
+     * @return the wrapped {@link NativeLibrary} instance
+     */
+    public static NativeLibrary getNativeLibrary(final Library library) {
+        if(library == null) {
+            throw new IllegalArgumentException("null passed to getNativeLibrary");
+        }
+        if(! Proxy.isProxyClass(library.getClass())) {
+            throw new IllegalArgumentException("library object passed to getNativeLibrary in not a proxy");
+        }
+        final InvocationHandler handler = Proxy.getInvocationHandler(library);
+        if (!(handler instanceof Library.Handler)) {
+            throw new IllegalArgumentException("Object is not a properly initialized Library interface instance");
+        }
+        return ((Library.Handler) handler).getNativeLibrary();
+    }
+
+    /**
+     * Get the {@link NativeLibrary} instance to which the given "registered"
+     * class is bound.
+     *
+     * @param cls the "registered" class, which was previously registered via
+     * the {@link Native#register register()} method
+     * @return the {@link NativeLibrary} instance to which the "registered"
+     * class is bound
+     */
+    public static NativeLibrary getNativeLibrary(final Class<?> cls) {
+        if(cls == null) {
+            throw new IllegalArgumentException("null passed to getNativeLibrary");
+        }
+        final Class<?> mappedClass = findDirectMappedClass(cls);
+        synchronized(registeredClasses) {
+            final NativeLibrary nativeLibrary = registeredLibraries.get(mappedClass);
+            if (nativeLibrary == null) {
+                throw new IllegalArgumentException("Class " + cls.getName() + " is not currently registered");
+            } else {
+                return nativeLibrary;
+            }
+        }
+    }
+
     /* Take note of options used for a given library mapping, to facilitate
      * looking them up later.
      */

test/com/sun/jna/NativeGetNativeLibraryTest.java

@@ -0,0 +1,94 @@
+/* Copyright (c) 2024 Matthias Bläsing, All Rights Reserved
+ *
+ * The contents of this file is dual-licensed under 2
+ * alternative Open Source/Free licenses: LGPL 2.1 or later and
+ * Apache License 2.0. (starting with JNA version 4.0.0).
+ *
+ * You can freely decide which license you want to apply to
+ * the project.
+ *
+ * You may obtain a copy of the LGPL License at:
+ *
+ * http://www.gnu.org/licenses/licenses.html
+ *
+ * A copy is also included in the downloadable source code package
+ * containing JNA, in file "LGPL2.1".
+ *
+ * You may obtain a copy of the Apache License at:
+ *
+ * http://www.apache.org/licenses/
+ *
+ * A copy is also included in the downloadable source code package
+ * containing JNA, in file "AL2.0".
+ */
+package com.sun.jna;
+
+import java.util.Collections;
+import junit.framework.TestCase;
+
+/**
+ * Check getNativeLibrary functions in Native
+ */
+public class NativeGetNativeLibraryTest extends TestCase {
+
+    private NativeLibrary libUTF8;
+    private TestLib libUTF8Interface;
+
+    @Override
+    protected void setUp() {
+        libUTF8 = NativeLibrary.getInstance("testlib",
+                Collections.singletonMap(Library.OPTION_STRING_ENCODING, "UTF-8"));
+        Native.register(TestLibUTF8.class, libUTF8);
+        libUTF8Interface = Native.load("testlib", TestLib.class,
+                Collections.singletonMap(Library.OPTION_STRING_ENCODING, "UTF-8"));
+    }
+
+    public void testGetNativeLibraryInterface() {
+        NativeLibrary nl = Native.getNativeLibrary(libUTF8Interface);
+        assertTrue(nl instanceof NativeLibrary);
+    }
+
+    public void testGetNativeLibraryDirect() {
+        NativeLibrary nl = Native.getNativeLibrary(TestLibUTF8.class);
+        assertTrue(nl instanceof NativeLibrary);
+        // This only makes sense for the direct case, as that directly wraps
+        // a supplied instance
+        assertEquals(libUTF8, nl);
+    }
+
+    public void testGetNativeLibraryOnUnboundShouldFail() {
+        try {
+            Native.getNativeLibrary(new TestLib() {
+                @Override
+                public String returnStringArgument(Pointer input) {
+                    return "";
+                }
+            });
+            assertTrue("Exception not thrown", false);
+        } catch (IllegalArgumentException ex) {
+            // This should be reached
+        }
+    }
+
+    public void testGetNativeLibraryOnNullShouldFail() {
+        try {
+            Native.getNativeLibrary((Class) null);
+            assertTrue("Exception not thrown", false);
+        } catch (IllegalArgumentException ex) {
+            // This should be reached
+        }
+    }
+
+    public static void main(java.lang.String[] argList) {
+        junit.textui.TestRunner.run(NativeGetNativeLibraryTest.class);
+    }
+
+    private static class TestLibUTF8 implements Library  {
+        native String returnStringArgument(Pointer input);
+    }
+
+    private interface TestLib extends Library {
+        public String returnStringArgument(Pointer input);
+    }
+
+}