Fix: some compilation issues

build.gradle

@@ -3,6 +3,15 @@ plugins {
     id 'application'
 }
 
+dependencies {
+    // JSON processing
+    implementation 'com.google.code.gson:gson:2.10.1'
+
+    // Testing
+    testImplementation 'org.junit.jupiter:junit-jupiter:5.10.1'
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+}
+
 java {
     toolchain {
         languageVersion = JavaLanguageVersion.of(24)
@@ -22,10 +31,24 @@ def bitcoinKernelHeader = file("${bitcoinCoreDir}/src/kernel/bitcoinkernel.h")
 tasks.register('buildBitcoinCore', Exec) {
     workingDir bitcoinCoreDir
 
-    // Configure Bitcoin Core build
+    // Configure Bitcoin Core build (matching rust-bitcoinkernel approach)
     commandLine 'cmake', '-B', 'build',
+            '-DCMAKE_BUILD_TYPE=RelWithDebInfo',
             '-DBUILD_KERNEL_LIB=ON',
-            '-DBUILD_UTIL_CHAINSTATE=ON'
+            '-DBUILD_TESTS=OFF',
+            '-DBUILD_KERNEL_TEST=OFF',
+            '-DBUILD_TX=OFF',
+            '-DBUILD_WALLET_TOOL=OFF',
+            '-DENABLE_WALLET=OFF',
+            '-DENABLE_EXTERNAL_SIGNER=OFF',
+            '-DBUILD_UTIL=OFF',
+            '-DBUILD_BITCOIN_BIN=OFF',
+            '-DBUILD_DAEMON=OFF',
+            '-DBUILD_UTIL_CHAINSTATE=OFF',
+            '-DBUILD_CLI=OFF',
+            '-DBUILD_SHARED_LIBS=ON',
+            '-DCMAKE_INSTALL_LIBDIR=lib',
+            '-DENABLE_IPC=OFF'
 
     // Only run if build directory doesn't exist or header has changed
 //    inputs.file bitcoinKernelHeader
@@ -65,4 +88,62 @@ application {
 }
 
 // Ensure proper build order
-compileJava.dependsOn compileBitcoinCore
+compileJava.dependsOn compileBitcoinCore
+
+// Configure test task
+test {
+    useJUnitPlatform()
+    testLogging {
+        events "passed", "skipped", "failed"
+        exceptionFormat "full"
+    }
+}
+
+// Task to run conformance handler
+tasks.register('conformanceHandler', Exec) {
+    group = 'conformance'
+    description = 'Run the conformance test handler (reads from stdin, writes to stdout)'
+
+    classpath = sourceSets.main.runtimeClasspath
+    mainClass = 'org.bitcoinkernel.conformance.ConformanceTestHandler'
+
+    // Required for FFM
+    jvmArgs = ['--enable-native-access=ALL-UNNAMED']
+
+    // Connect stdin/stdout
+    standardInput = System.in
+    standardOutput = System.out
+    standardError = System.err
+}
+
+// Build uber JAR with all dependencies
+tasks.register('buildConformanceJar', Jar) {
+    group = 'conformance'
+    description = 'Build standalone conformance handler JAR with all dependencies'
+
+    archiveBaseName = 'java-bitcoinkernel-conformance-handler'
+    archiveVersion = '0.1.0'
+
+    from sourceSets.main.output
+
+    // Include all dependencies
+    from {
+        configurations.runtimeClasspath.collect {
+            it.isDirectory() ? it : zipTree(it)
+        }
+    }
+
+    // Avoid duplicate files
+    duplicatesStrategy = DuplicatesStrategy.EXCLUDE
+
+    manifest {
+        attributes(
+                'Main-Class': 'org.bitcoinkernel.conformance.ConformanceTestHandler',
+                'Implementation-Title': 'Java Bitcoin Kernel Conformance Handler',
+                'Implementation-Version': archiveVersion.get()
+        )
+    }
+}
+
+// Make conformance JAR depend on compilation
+buildConformanceJar.dependsOn compileJava

src/main/java/org/bitcoinkernel/KernelData.java

@@ -49,14 +49,19 @@ public int verify(long amount, Transaction txTo, TransactionOutput[] spentOutput
             txTo.checkClosed();
 
             try (var arena = Arena.ofConfined()) {
-                // Allocate array of output pointers
-                MemorySegment outputPtrs = arena.allocate(
-                    ValueLayout.ADDRESS,
-                    spentOutputs.length
-                );
-
-                for (int i = 0; i < spentOutputs.length; i++) {
-                    outputPtrs.setAtIndex(ValueLayout.ADDRESS, i, spentOutputs[i].getInner());
+                // Prepare spent outputs array
+                int numOutputs = (spentOutputs != null) ? spentOutputs.length : 0;
+                MemorySegment outputPtrs;
+
+                if (numOutputs > 0) {
+                    // Allocate array of output pointers
+                    outputPtrs = arena.allocate(ValueLayout.ADDRESS, numOutputs);
+                    for (int i = 0; i < spentOutputs.length; i++) {
+                        outputPtrs.setAtIndex(ValueLayout.ADDRESS, i, spentOutputs[i].getInner());
+                    }
+                } else {
+                    // Pass NULL for empty/null spent outputs
+                    outputPtrs = MemorySegment.NULL;
                 }
 
                 MemorySegment statusPtr = arena.allocate(ValueLayout.JAVA_BYTE);
@@ -66,13 +71,14 @@ public int verify(long amount, Transaction txTo, TransactionOutput[] spentOutput
                     amount,
                     txTo.getInner(),
                     outputPtrs,
-                    spentOutputs.length,
+                    numOutputs,
                     inputIndex,
                     flags,
                     statusPtr
                 );
 
-                if (result != 0) {
+                // Note: return value 1 = success, 0 = error
+                if (result == 0) {
                     byte status = statusPtr.get(ValueLayout.JAVA_BYTE, 0);
                     throw new KernelTypes.KernelException(
                         KernelTypes.KernelException.ScriptVerifyError.fromNative(status)

src/main/java/org/bitcoinkernel/Transactions.java

@@ -84,7 +84,7 @@ MemorySegment getInner() {
         }
 
         @Override
-        public void close() throws Exception {
+        public void close() {
             if (inner != MemorySegment.NULL) {
                 btck_transaction_destroy(inner);
                 inner = MemorySegment.NULL;
@@ -264,7 +264,7 @@ MemorySegment getInner() {
         }
 
         @Override
-        public void close() throws Exception {
+        public void close() {
             if (inner != MemorySegment.NULL && ownsMemory) {
                 btck_transaction_output_destroy(inner);
                 inner = MemorySegment.NULL;

src/main/java/org/bitcoinkernel/jextract/bitcoinkernel_h.java

@@ -20,8 +20,25 @@ public class bitcoinkernel_h extends bitcoinkernel_h$shared {
 
     static final Arena LIBRARY_ARENA = Arena.ofAuto();
 
-    static final SymbolLookup SYMBOL_LOOKUP = SymbolLookup.loaderLookup()
-            .or(Linker.nativeLinker().defaultLookup());
+    static final SymbolLookup SYMBOL_LOOKUP;
+
+    static {
+        // Load the bitcoinkernel library
+        SymbolLookup lookup = null;
+        try {
+            System.loadLibrary("bitcoinkernel");
+            lookup = SymbolLookup.loaderLookup();
+        } catch (UnsatisfiedLinkError e) {
+            // Fall back to default lookup (LD_LIBRARY_PATH)
+            System.err.println("Warning: Could not load libbitcoinkernel via System.loadLibrary, trying LD_LIBRARY_PATH");
+        }
+
+        if (lookup == null) {
+            lookup = Linker.nativeLinker().defaultLookup();
+        }
+
+        SYMBOL_LOOKUP = lookup;
+    }
 
     private static final int __WORDSIZE = (int)64L;
     /**