jni.cpp

// A simple wrapper.
// 
// In Java:
//
// static String getString(String key);
//
// Calls the C++ function:
//
// C++: std::string openmpt::string::get(std::string &key);
//
// TODO: Might leak memory on exception throw. See within.
JNIEXPORT jstring JNICALL Java_com_mrb0_OpenMPT_getString
  (JNIEnv *env, jclass, jstring keyJString) {

    jstring charsetUtf8 = env->NewStringUTF("UTF-8");
    if (charsetUtf8 == NULL) {
        return NULL;
    }

    jclass clsString = env->FindClass("java/lang/String");
    if (clsString == NULL) {
        return NULL;
    }

    jmethodID getBytes = env->GetMethodID(clsString, "getBytes", "(Ljava/lang/String;)[B");
    if (getBytes == NULL) {
        return NULL;
    }

    jbyteArray keyStringBytesJArray = (jbyteArray)env->CallObjectMethod(keyJString, getBytes, charsetUtf8);
    if (env->ExceptionOccurred()) {
        return NULL;
    }

    jsize keyStringBytesLength = env->GetArrayLength(keyStringBytesJArray);
    if (env->ExceptionOccurred()) {
        return NULL;
    }

    jbyte *keyStringBytesArray = env->GetByteArrayElements(keyStringBytesJArray, NULL);
    if (keyStringBytesArray == NULL) {
        return NULL;
    }

    std::string keyStdString((char *)keyStringBytesArray, keyStringBytesLength);

    // TODO: Call this even if an exception is thrown after GetByteArrayElements.
    env->ReleaseByteArrayElements(keyStringBytesJArray, keyStringBytesArray, JNI_ABORT);
    if (env->ExceptionOccurred()) {
        return NULL;
    }

    std::string value = openmpt::string::get(keyStdString);

    jbyteArray valueBytesJArray = (jbyteArray)env->NewByteArray(value.size());
    if (valueBytesJArray == NULL) {
        return NULL;
    }

    jbyte *valueBytesArray = env->GetByteArrayElements(valueBytesJArray, NULL);
    if (valueBytesArray == NULL) {
        return NULL;
    }

    jbyte *nextArrayPos = valueBytesArray;
    for (char &c : value) {
        *(nextArrayPos++) = c;
    }

    // TODO: Call this even if an exception is thrown after GetByteArrayElements.
    env->ReleaseByteArrayElements(valueBytesJArray, valueBytesArray, 0);
    if (env->ExceptionOccurred()) {
        return NULL;
    }

    jmethodID newStringBytesCharset = env->GetMethodID(clsString, "<init>", "([BLjava/lang/String;)V");
    if (newStringBytesCharset == NULL) {
        return NULL;
    }

    return (jstring)env->NewObject(clsString, newStringBytesCharset, valueBytesJArray, charsetUtf8);
}