add another test that uses MemorySegment to pass an array copy to Swift (ffm)

Author: ktoso

Samples/SwiftJavaExtractFFMSampleApp/Sources/MySwiftLibrary/MySwiftLibrary.swift

@@ -63,6 +63,24 @@ public func withBuffer(body: (UnsafeRawBufferPointer) -> Void) {
   body(globalBuffer)
 }
 
+public func getArray() -> [UInt8] {
+  return [1, 2, 3]
+}
+
+public func sumAllByteArrayElements(actuallyAnArray: UnsafeRawPointer, count: Int) -> Int {
+  let bufferPointer = UnsafeRawBufferPointer(start: actuallyAnArray, count: count)
+  let array = Array(bufferPointer)
+  return Int(array.reduce(0, { partialResult, element in partialResult + element }))
+}
+
+public func sumAllByteArrayElements(array: [UInt8]) -> Int {
+  return Int(array.reduce(0, { partialResult, element in partialResult + element }))
+}
+
+public func withArray(body: ([UInt8]) -> Void) {
+  body([1, 2, 3])
+}
+
 public func globalReceiveSomeDataProtocol(data: some DataProtocol) -> Int {
   p(Array(data).description)
   return data.count

Samples/SwiftJavaExtractFFMSampleApp/src/test/java/com/example/swift/WithBufferTest.java

@@ -20,7 +20,10 @@
 
 import static org.junit.jupiter.api.Assertions.*;
 
+import java.lang.foreign.ValueLayout;
+import java.util.Arrays;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.stream.IntStream;
 
 public class WithBufferTest {
     @Test
@@ -33,4 +36,25 @@ void test_withBuffer() {
 
         assertEquals(124, bufferSize.get());
     }
+
+    @Test
+    void test_sumAllByteArrayElements_throughMemorySegment() {
+        byte[] bytes =  new byte[124];
+        Arrays.fill(bytes, (byte) 1);
+
+        try (var arena = AllocatingSwiftArena.ofConfined()) {
+            // NOTE: We cannot use MemorySegment.ofArray because that creates a HEAP backed segment and therefore cannot pass into native:
+            //         java.lang.IllegalArgumentException: Heap segment not allowed: MemorySegment{ kind: heap, heapBase: [B@5b6ec132, address: 0x0, byteSize: 124 }
+            //            MemorySegment bytesSegment = MemorySegment.ofArray(bytes); // NO COPY (!)
+            //            MySwiftLibrary.sumAllByteArrayElements(bytesSegment, bytes.length);
+
+            var bytesCopy = arena.allocateFrom(ValueLayout.JAVA_BYTE, bytes);
+            var swiftSideSum = MySwiftLibrary.sumAllByteArrayElements(bytesCopy, bytes.length);
+
+            System.out.println("swiftSideSum = " + swiftSideSum);
+
+            int javaSideSum = IntStream.range(0, bytes.length).map(i -> bytes[i]).sum();
+            assertEquals(javaSideSum, swiftSideSum);
+        }
+    }
 }