jni: release string characters in conversion to Go string

This change should fix #13 by releasing the string buffer from the JVM after we
convert the string to a Go string. However, I've been having a lot of trouble
building the tests on Linux, and I've run out of time to keep messing with it.
I'm posting this patch in the hope that someone else is better positioned to
validate it. Please do not merge this unless you can verify that it works
properly.

Signed-off-by: Chris Waldon <christopher.waldon.dev@gmail.com>

gojni.h

@@ -15,6 +15,7 @@ __attribute__ ((visibility ("hidden"))) jfieldID _jni_GetFieldID(JNIEnv *env, jc
 __attribute__ ((visibility ("hidden"))) jfieldID _jni_GetStaticFieldID(JNIEnv *env, jclass clazz, const char *name, const char *sig);
 __attribute__ ((visibility ("hidden"))) jsize _jni_GetStringLength(JNIEnv *env, jstring str);
 __attribute__ ((visibility ("hidden"))) const jchar *_jni_GetStringChars(JNIEnv *env, jstring str);
+__attribute__ ((visibility ("hidden"))) void _jni_ReleaseStringChars(JNIEnv *env, jstring str, const jchar *chars);
 __attribute__ ((visibility ("hidden"))) jstring _jni_NewString(JNIEnv *env, const jchar *unicodeChars, jsize len);
 __attribute__ ((visibility ("hidden"))) jboolean _jni_IsSameObject(JNIEnv *env, jobject ref1, jobject ref2);
 __attribute__ ((visibility ("hidden"))) jboolean _jni_IsInstanceOf(JNIEnv *env, jobject obj, jclass cls);
@@ -23,6 +24,7 @@ __attribute__ ((visibility ("hidden"))) void _jni_DeleteGlobalRef(JNIEnv *env, j
 __attribute__ ((visibility ("hidden"))) jobject _jni_NewLocalRef(JNIEnv *env, jobject obj);
 __attribute__ ((visibility ("hidden"))) void _jni_DeleteLocalRef(JNIEnv *env, jobject obj);
 __attribute__ ((visibility ("hidden"))) jint _jni_CallStaticIntMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args);
+__attribute__ ((visibility ("hidden"))) jboolean _jni_CallStaticBooleanMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args);
 __attribute__ ((visibility ("hidden"))) jobject _jni_CallStaticObjectMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args);
 __attribute__ ((visibility ("hidden"))) jobject _jni_NewObjectA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args);
 __attribute__ ((visibility ("hidden"))) void _jni_CallStaticVoidMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args);

jni.c

@@ -78,6 +78,10 @@ const jchar *_jni_GetStringChars(JNIEnv *env, jstring str) {
 	return (*env)->GetStringChars(env, str, NULL);
 }
 
+void _jni_ReleaseStringChars(JNIEnv *env, jstring str, const jchar *chars) {
+	(*env)->ReleaseStringChars(env, str, chars);
+}
+
 jstring _jni_NewString(JNIEnv *env, const jchar *unicodeChars, jsize len) {
 	return (*env)->NewString(env, unicodeChars, len);
 }
@@ -118,6 +122,10 @@ jint _jni_CallStaticIntMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue
 	return (*env)->CallStaticIntMethodA(env, cls, method, args);
 }
 
+jboolean _jni_CallStaticBooleanMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args) {
+	return (*env)->CallStaticBooleanMethodA(env, cls, method, args);
+}
+
 jobject _jni_CallStaticObjectMethodA(JNIEnv *env, jclass cls, jmethodID method, jvalue *args) {
 	return (*env)->CallStaticObjectMethodA(env, cls, method, args);
 }

jni.go

@@ -104,6 +104,12 @@ func CallStaticIntMethod(e Env, cls Class, method MethodID, args ...Value) (int,
 	return int(res), exception(e)
 }
 
+// CallStaticBooleanMethod calls a static method on a Java class, returning an int.
+func CallStaticBooleanMethod(e Env, cls Class, method MethodID, args ...Value) (bool, error) {
+	res := C._jni_CallStaticBooleanMethodA(e.env, C.jclass(cls), C.jmethodID(method), varArgs(args))
+	return res == TRUE, exception(e)
+}
+
 // FindClass returns a reference to a Java class with a given name, using the
 // JVM's default class loader. Any exceptions caused by the underlying JNI call
 // (for example if the class is not found) will result in a panic.
@@ -405,6 +411,10 @@ func GoString(e Env, str String) string {
 	}
 	strlen := C._jni_GetStringLength(e.env, C.jstring(str))
 	chars := C._jni_GetStringChars(e.env, C.jstring(str))
+	if chars == nil {
+		return ""
+	}
+	defer C._jni_ReleaseStringChars(e.env, C.jstring(str), chars)
 	var utf16Chars []uint16
 	hdr := (*reflect.SliceHeader)(unsafe.Pointer(&utf16Chars))
 	hdr.Data = uintptr(unsafe.Pointer(chars))

jni_test.go

@@ -198,6 +198,44 @@ func TestStaticObjectMethod(t *testing.T) {
 	}
 }
 
+func TestStaticBooleanMethod(t *testing.T) {
+	err := Do(vm, func(env Env) error {
+		cls := FindClass(env, "test/AClass")
+		mid := GetStaticMethodID(env, cls, "GetStaticBoolean", "()Z")
+		if mid == nil {
+			t.Errorf("MethodID is nil")
+		}
+		setterMid := GetStaticMethodID(env, cls, "SetStaticBoolean", "(Z)V")
+		if setterMid == nil {
+			t.Errorf("Setter MethodID is nil")
+		}
+		res, err := CallStaticBooleanMethod(env, cls, mid)
+		if err != nil {
+			t.Errorf("Method invocation failed")
+		}
+		if !res {
+			t.Errorf("Method returned %v, not expected value of %v.", res, true)
+		}
+		if err := CallStaticVoidMethod(env, cls, setterMid, FALSE); err != nil {
+			t.Errorf("Setter invocation failed")
+		}
+		res, err = CallStaticBooleanMethod(env, cls, mid)
+		if err != nil {
+			t.Errorf("Method invocation failed")
+		}
+		if res {
+			t.Errorf("Method returned %v, not expected value of %v.", res, false)
+		}
+		if err := CallStaticVoidMethod(env, cls, setterMid, TRUE); err != nil {
+			t.Errorf("Setter invocation failed")
+		}
+		return err
+	})
+	if err != nil {
+		t.Errorf("Error: %s", err)
+	}
+}
+
 func TestMethod(t *testing.T) {
 	defer func() {
 		if r := recover(); r == nil {

test/AClass.java

@@ -47,7 +47,7 @@ public class AClass {
 	private float pfl = (float)2.2;
 	private double pdb = 1001.1001;
 
-	public static Boolean GetStaticBoolean() {
+	public static boolean GetStaticBoolean() {
 		return staticbl;
 	}
 
@@ -75,6 +75,10 @@ public class AClass {
 		return staticobj;
 	}
 
+	public static void SetStaticBoolean(boolean val) {
+		staticbl = val;
+	}
+
 	public void IncInt() {
 		in = in + 1;
 	}