Add GetProcAddress to allow accessing functions exported by ordinal

CHANGES.md

@@ -60,6 +60,7 @@ Features
 * [#680](https://github.com/java-native-access/jna/pull/680): Added `SetCurrentProcessExplicitAppUserModelID` and `GetCurrentProcessExplicitAppUserModelID` to `com.sun.jna.platform.win32.Shell32` for setting the [System.AppUserModel.ID](https://msdn.microsoft.com/en-us/library/windows/desktop/dd391569.aspx) of the host process - [@rednoah](https://github.com/rednoah).
 * [#693](https://github.com/java-native-access/jna/pull/693): Bind DDEML (Dynamic Data Exchange Management Library), add a thread implementation that runs a windows message loop - [@matthiasblaesing](https://github.com/matthiasblaesing).
 * [#702](https://github.com/java-native-access/jna/pull/702): Added `GetClientRect` to `com/sun/jna/platform/win32/User32` - [@Jonatino](https://github.com/Jonatino).
+* [#689](https://github.com/java-native-access/jna/pull/689): Add `GetProcAddress(HMODULE, int)` to `com.sun.jna.platform.win32.Kernel32` - [@matthiasblaesing](https://github.com/matthiasblaesing).
 
 Bug Fixes
 ---------

contrib/platform/src/com/sun/jna/platform/win32/Kernel32.java

@@ -12,6 +12,7 @@
  */
 package com.sun.jna.platform.win32;
 
+import com.sun.jna.LastErrorException;
 import com.sun.jna.Native;
 import com.sun.jna.Pointer;
 import com.sun.jna.ptr.IntByReference;
@@ -3353,4 +3354,25 @@ boolean GetVolumePathNamesForVolumeName(String lpszVolumeName,
      *         flags.
      */
     int SetErrorMode(int umode);
+
+    /**
+     * Retrieves the address of an exported function or variable from the
+     * specified dynamic-link library (DLL).
+     *
+     * <p>
+     * This function is mapped to enable accessing function on win32 systems
+     * only accessible by their ordinal value.</p>
+     *
+     * <p>
+     * To access functions by their name, please use
+     * NativeLibrary#getFunction.</p>
+     *
+     * @param hmodule A handle to the DLL module that contains the function or
+     *                variable. The LoadLibrary, LoadLibraryEx,
+     *                LoadPackagedLibrary, or GetModuleHandle function returns
+     *                this handle.
+     * @param ordinal ordinal value of the function export
+     * @return address of the exported function
+     */
+    Pointer GetProcAddress(HMODULE hmodule, int ordinal) throws LastErrorException;
 }

contrib/platform/test/com/sun/jna/platform/win32/Kernel32Test.java

@@ -12,6 +12,7 @@
  */
 package com.sun.jna.platform.win32;
 
+import com.sun.jna.Function;
 import java.io.BufferedReader;
 import java.io.BufferedWriter;
 import java.io.File;
@@ -30,6 +31,7 @@
 
 import com.sun.jna.Memory;
 import com.sun.jna.Native;
+import com.sun.jna.NativeLibrary;
 import com.sun.jna.NativeMappedConverter;
 import com.sun.jna.Platform;
 import com.sun.jna.Pointer;
@@ -1158,4 +1160,33 @@ public void testSetErrorMode() {
         // Restore to previous state; 0x0001 is now "previous"
         assertEquals(Kernel32.INSTANCE.SetErrorMode(previousMode), 0x0001);
     }
+
+    /**
+     * Test that a named function on win32 can be equally resolved by its ordinal
+     * value.
+     * 
+     * From link.exe /dump /exports c:\\Windows\\System32\\kernel32.dll
+     * 
+     *  746  2E9 0004FA20 GetTapeStatus
+     *  747  2EA 0002DB20 GetTempFileNameA
+     *  748  2EB 0002DB30 GetTempFileNameW
+     *  749  2EC 0002DB40 GetTempPathA
+     *  750  2ED 0002DB50 GetTempPathW
+     *  751  2EE 00026780 GetThreadContext
+     * 
+     * The tested function is GetTempPathW which is mapped to the ordinal 750.
+     */
+    public void testGetProcAddress() {
+        NativeLibrary kernel32Library = NativeLibrary.getInstance("kernel32");
+        // get module handle needed to resolve function pointer via GetProcAddress
+        HMODULE kernel32Module = Kernel32.INSTANCE.GetModuleHandle("kernel32");
+
+        Function namedFunction = kernel32Library.getFunction("GetTempPathW");
+        long namedFunctionPointerValue = Pointer.nativeValue(namedFunction);
+
+        Pointer ordinalFunction = Kernel32.INSTANCE.GetProcAddress(kernel32Module, 750);
+        long ordinalFunctionPointerValue = Pointer.nativeValue(ordinalFunction);
+
+        assertEquals(namedFunctionPointerValue, ordinalFunctionPointerValue);
+    }
 }

src/com/sun/jna/Function.java

@@ -141,7 +141,7 @@ public static Function getFunction(String libraryName, String functionName, int
      * @param   p       Native function pointer
      */
     public static Function getFunction(Pointer p) {
-        return getFunction(p, 0);
+        return getFunction(p, 0, null);
     }
 
     /**
@@ -159,7 +159,28 @@ public static Function getFunction(Pointer p) {
      *                  Function <a href="#callflags">call flags</a>
      */
     public static Function getFunction(Pointer p, int callFlags) {
-        return new Function(p, callFlags, null);
+        return getFunction(p, callFlags, null);
+    }
+
+    /**
+     * Obtain a <code>Function</code> representing a native
+     * function pointer.  In general, this function should be used by dynamic
+     * languages; Java code should allow JNA to bind to a specific Callback
+     * interface instead by defining a return type or Structure field type.
+     *
+     * <p>The allocated instance represents a pointer to the native
+     * function pointer.
+     *
+     * @param   p
+     *                  Native function pointer
+     * @param   callFlags
+     *                  Function <a href="#callflags">call flags</a>
+     * @param   encoding
+     *                  Encoding to use for conversion between Java and native
+     *                  strings.
+     */
+    public static Function getFunction(Pointer p, int callFlags, String encoding) {
+        return new Function(p, callFlags, encoding);
     }
 
     // Keep a reference to the NativeLibrary so it does not get garbage