JNA with JDK 22 java.lang.foreign

Harri Pesonen

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Apr 10, 2024, 7:31:07 AMApr 10

to Java Native Access

Hello, I have been using JNA for years, but only one function to read Windows registry.

Now that JDK 22 is released, I though of implementing that function with java.lang.foreign.

This is it:

Advapi32Util.java

public static TreeMap<String, Object> registryGetValues(HKEY root,
String keyPath, int samDesiredExtra) {
try (Arena arena = Arena.ofConfined()) {
SymbolLookup advapi32 = SymbolLookup.libraryLookup("Advapi32", Arena.global());
Linker linker = Linker.nativeLinker();
MemorySegment hKeyRef = arena.allocate(JAVA_LONG);
Object o;
try {
o = linker.downcallHandle(
advapi32.find("RegOpenKeyExW").orElseThrow(),
FunctionDescriptor.of(
JAVA_INT, // return 0 = ERROR_SUCCESS
JAVA_LONG, // HKey
ADDRESS, // sub key
JAVA_INT, // options
JAVA_INT, // samDesired
ADDRESS // address of returned handle
))
.invoke(
Pointer.nativeValue(root.getPointer()),
arena.allocateFrom(keyPath, StandardCharsets.UTF_16LE),
0, // options
WinNT.KEY_READ | samDesiredExtra,
hKeyRef
);
} catch (Throwable e) {
throw new RuntimeException(e);
}
int rc = (int)(Integer)o;
if (rc != W32Errors.ERROR_SUCCESS) {
throw new RuntimeException("RegOpenKeyExA " + rc);
// throw new Win32Exception(rc);
}
long hKey = hKeyRef.get(JAVA_LONG, 0);
try {
return registryGetValues(advapi32, arena, hKey);
} finally {
try {
o = linker.downcallHandle(
advapi32.find("RegCloseKey").orElseThrow(),
FunctionDescriptor.of(
JAVA_INT, // return 0 = ERROR_SUCCESS
JAVA_LONG // HKey
))
.invoke(hKey);
rc = (int)(Integer)o;
if (rc != W32Errors.ERROR_SUCCESS) {
log.log(System.Logger.Level.ERROR, "RegCloseKey", rc);
// throw new Win32Exception(rc);
}
} catch (Throwable e) {
log.log(System.Logger.Level.ERROR, "RegCloseKey", e);
}
}
}
}

public static TreeMap<String, Object> registryGetValues(SymbolLookup advapi32, Arena arena,
long hKey) {
TreeMap<String, Object> keyValues = new TreeMap<>();
Linker linker = Linker.nativeLinker();
MemorySegment lpcValues = arena.allocate(JAVA_INT);
MemorySegment lpcMaxValueNameLen = arena.allocate(JAVA_INT);
MemorySegment lpcMaxValueLen = arena.allocate(JAVA_INT);
Object o;
try {
o = linker.downcallHandle(
advapi32.find("RegQueryInfoKeyA").orElseThrow(),
FunctionDescriptor.of(
JAVA_INT, // return 0 = ERROR_SUCCESS
JAVA_LONG, // HKey
ADDRESS, // lpClass
ADDRESS, // lpClass
ADDRESS, // lpReserved
ADDRESS, // lpcSubkeys
ADDRESS, // lpcMaxSubKeyLen
ADDRESS, // lpcMaxClassLen
ADDRESS, // lpcValues
ADDRESS, // lpcMaxValueNameLen
ADDRESS, // lpcMaxValueLen
ADDRESS, // lpcbSecurityDescriptor
ADDRESS // lpftLastWriteTime
))
.invoke(
hKey,
MemorySegment.NULL, // lpClass
MemorySegment.NULL, // lpClass
MemorySegment.NULL, // lpReserved
MemorySegment.NULL, // lpcSubkeys
MemorySegment.NULL, // lpcMaxSubKeyLen
MemorySegment.NULL, // lpcMaxClassLen
lpcValues,
lpcMaxValueNameLen,
lpcMaxValueLen,
MemorySegment.NULL, // lpcbSecurityDescriptor
MemorySegment.NULL // lpftLastWriteTime
);
} catch (Throwable e) {
throw new RuntimeException(e);
}
int rc = (int) (Integer) o;
if (rc != W32Errors.ERROR_SUCCESS) {
throw new RuntimeException("RegQueryInfoKeyW " + rc);
// throw new Win32Exception(rc);
}
int maxValueNameLen = lpcMaxValueNameLen.get(JAVA_INT, 0);
MemorySegment name = arena.allocate(JAVA_CHAR, maxValueNameLen + 1);
// Allocate enough memory to hold largest value and two
// terminating WCHARs -- the memory is zeroed so after
// value request we should not overread when reading strings
int maxValueLen = lpcMaxValueLen.get(JAVA_INT, 0);
MemorySegment byteData = arena.allocate(JAVA_CHAR, maxValueLen + 2);
int valueCount = lpcValues.get(JAVA_INT, 0);
MemorySegment lpcchValueName = arena.allocate(JAVA_INT);
MemorySegment lpcbData = arena.allocate(JAVA_INT);
MemorySegment lpType = arena.allocate(JAVA_INT);
for (int i = 0; i < valueCount; i++) {
byteData.asByteBuffer().clear(); // TODO: Arrays.fill(b.array(), (byte)0) ???
lpcchValueName.set(JAVA_INT, 0, maxValueLen + 1);
lpcbData.set(JAVA_INT, 0, maxValueLen);
try {
o = linker.downcallHandle(
advapi32.find("RegEnumValueW").orElseThrow(),
FunctionDescriptor.of(
JAVA_INT, // return 0 = ERROR_SUCCESS
JAVA_LONG, // HKey
JAVA_INT, // dwIndex
ADDRESS, // lpValueName
ADDRESS, // lpcchValueName
ADDRESS, // reserved
ADDRESS, // lpType
ADDRESS, // lpData
ADDRESS // lpcbData
))
.invoke(hKey, i, name, lpcchValueName, MemorySegment.NULL, lpType, byteData, lpcbData);

} catch (Throwable e) {
throw new RuntimeException(e);
}
rc = (int) (Integer) o;
if (rc != W32Errors.ERROR_SUCCESS) {
throw new RuntimeException("RegEnumValueW " + rc);
// throw new Win32Exception(rc);
}
String nameString = name.getString(0, StandardCharsets.UTF_16LE);
int dataSize = lpcbData.get(JAVA_INT, 0);
int type = lpType.get(JAVA_INT, 0);
if (dataSize == 0) {
switch (type) {
case WinNT.REG_BINARY: {
keyValues.put(nameString, new byte[0]);
break;
}
case WinNT.REG_SZ:
case WinNT.REG_EXPAND_SZ: {
keyValues.put(nameString, new char[0]);
break;
}
case WinNT.REG_MULTI_SZ: {
keyValues.put(nameString, new String[0]);
break;
}
case WinNT.REG_NONE: {
keyValues.put(nameString, null);
break;
}
default:
throw new RuntimeException("Unsupported empty type: " + type);
}
continue;
}
switch (type) {
case WinNT.REG_QWORD: {
keyValues.put(nameString, byteData.get(JAVA_LONG, 0));
break;
}
case WinNT.REG_DWORD: {
keyValues.put(nameString, byteData.get(JAVA_INT, 0));
break;
}
case WinNT.REG_SZ:
case WinNT.REG_EXPAND_SZ: {
keyValues.put(nameString, byteData.getString(0, StandardCharsets.UTF_16LE));
break;
}
case WinNT.REG_BINARY: {
byte[] buf = new byte[dataSize];
byteData.asByteBuffer().limit(dataSize).get(buf);
keyValues.put(nameString, buf);
break;
}
case WinNT.REG_MULTI_SZ: {
ArrayList<String> result = new ArrayList<>();
int offset = 0;
while (offset < dataSize) {
String s = byteData.getString(offset, StandardCharsets.UTF_16LE);
offset += s.length() * 2; // TODO: ???
offset += 2;
if (s.isEmpty()) {
// A sequence of null-terminated strings,
// terminated by an empty string (\0).
// => The first empty string terminates the
break;
} else {
result.add(s);
}
}
keyValues.put(nameString, result.toArray(new String[0]));
break;
}
default:
throw new RuntimeException("Unsupported type: " + type);
}
}
return keyValues;
}

It works fine, but unfortunately I can't use it yet because we are still targeting Java 11.

Posting this if this is useful for someone.

Converting JNA to java.lang.foreign is quite straightforward, but quite a lot of work.

This took me one day.

Wondering if we get JNA for JDK 22 later?

-Harri

Harri Pesonen

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Apr 10, 2024, 11:14:24 AMApr 10

to Java Native Access

I implemented one more function to get the error message from Windows. Here I use fixed buffer instead of WIndows allocated buffer, because I didn't find a secure way access that returned buffer.

Here you can see my java.lang.foreign code before the original JNA code.

public static String formatMessage(int code, int primaryLangId, int sublangId) {
if (!Native.jni) {
SymbolLookup kernel32 = SymbolLookup.libraryLookup("kernel32", Arena.global());
Linker linker = Linker.nativeLinker();

try (Arena arena = Arena.ofConfined()) {

int bufferSize = 128;
MemorySegment buffer = arena.allocate(JAVA_CHAR, bufferSize);

Object o;
try {
o = linker.downcallHandle(

kernel32.find("FormatMessageW").orElseThrow(),
FunctionDescriptor.of(
JAVA_INT, // return nLen
JAVA_INT, // int dwFlags
ADDRESS, // Pointer lpSource
JAVA_INT, // int dwMessageId
JAVA_INT, // int dwLanguageId
ADDRESS, // PointerByReference lpBuffer
JAVA_INT, // int nSize
ADDRESS// Pointer va_list
))
.invoke(
// WinBase.FORMAT_MESSAGE_ALLOCATE_BUFFER |
WinBase.FORMAT_MESSAGE_FROM_SYSTEM
| WinBase.FORMAT_MESSAGE_IGNORE_INSERTS,
MemorySegment.NULL,
code,
WinNT.LocaleMacros.MAKELANGID(primaryLangId, sublangId),
buffer, bufferSize, MemorySegment.NULL

);
} catch (Throwable e) {
throw new RuntimeException(e);
}

int len = (int)(Integer)o;
if (len == 0) {
throw new LastErrorException("Error " + code);
}
return buffer.getString(0, StandardCharsets.UTF_16LE);
}
} // end of java.lang.foreign, start of original JNA code
PointerByReference buffer = new PointerByReference();
int nLen = Kernel32.INSTANCE.FormatMessage(
WinBase.FORMAT_MESSAGE_ALLOCATE_BUFFER
| WinBase.FORMAT_MESSAGE_FROM_SYSTEM
| WinBase.FORMAT_MESSAGE_IGNORE_INSERTS,
null,
code,
WinNT.LocaleMacros.MAKELANGID(primaryLangId, sublangId),
buffer, 0, null);
if (nLen == 0) {
throw new LastErrorException(Native.getLastError());
}

Pointer ptr = buffer.getValue();
try {
String s = ptr.getWideString(0);
return s.trim();
} finally {
freeLocalMemory(ptr);
}
}

Markus Karg

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Apr 18, 2024, 4:36:44 AMApr 18

to Java Native Access

Maybe you like to give jextract a try? It is still a beta, but it should already be able to generate all that code for you, and possibly it spares you some potential bugs. :-)

Harri Pesonen

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Apr 23, 2024, 6:47:08 AMApr 23

to Java Native Access

Yes, certainly I will try jextract at some point.

But now I have been playing with JNA, changing it to use FFM instead of JNI.

I have a fork here:

https://github.com/Fuerte1/jna-foreign

This is a hobby project, hopefully useful for someone.

Status of JNA unit tests:
* Tests failed: 206, passed: 431, ignored: 24 of 661 tests

Status of Win32 platform unit tests:
* Tests failed: 143, passed: 502, ignored: 13 of 658 tests (COM tests skipped)

Most standard JNA features work.
Does not work:
* By-value structures larger than 8 bytes (8 bytes fit into Java long)
* Java objects (native libraries normally do not use or return Java objects)
* Varargs
* ...

Markus Karg

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Apr 23, 2024, 7:22:49 AMApr 23

to Java Native Access

Cool! Maybe some day JNA will have with customizable backends? :-)

Harri Pesonen

unread,

Apr 23, 2024, 12:52:05 PMApr 23

to jna-...@googlegroups.com

Yes, certainly I will try jextract at some point.

But now I have been playing with JNA, changing it to use FFM instead of JNI.

I have a fork here:

https://github.com/Fuerte1/jna-foreign

This is a hobby project, hopefully useful for someone.

Status of JNA unit tests:
* Tests failed: 206, passed: 431, ignored: 24 of 661 tests

Status of Win32 platform unit tests:
* Tests failed: 143, passed: 502, ignored: 13 of 658 tests (COM tests skipped)

Most standard JNA features work.
Does not work:
* By-value structures larger than 8 bytes (8 bytes fit into Java long) 
* Java objects (native libraries normally do not use or return Java objects)
* Varargs
* ...

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