Introduce JniString as C++ wrapper over jstring

We used to manually call JNI UTF-8 string allocation and deallocation functions when utilizing a `jstring` but this could be erroneous and is just inconvenient. All of this has now been consolidated into an class `JniString` which is a wrapper around `std::string` and creates a copy of the contents of the `jstring` in its constructor and passes them into the `std::string` constructor.

app/src/main/cpp/emu_jni.cpp

@@ -76,8 +76,8 @@ extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_executeApplication(
     auto settings{std::make_shared<skyline::Settings>(preferenceFd)};
     close(preferenceFd);
 
-    auto appFilesPath{env->GetStringUTFChars(appFilesPathJstring, nullptr)};
+    skyline::JniString appFilesPath(env, appFilesPathJstring);
-    auto logger{std::make_shared<skyline::Logger>(std::string(appFilesPath) + "skyline.log", settings->logLevel)};
+    auto logger{std::make_shared<skyline::Logger>(appFilesPath + "skyline.log", settings->logLevel)};
 
     auto start{std::chrono::steady_clock::now()};
 
@@ -92,7 +92,7 @@ extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_executeApplication(
             jvmManager,
             logger,
             settings,
-            std::string(appFilesPath),
+            appFilesPath,
             GetTimeZoneName(),
             static_cast<skyline::language::SystemLanguage>(systemLanguage),
             std::make_shared<skyline::vfs::AndroidAssetFileSystem>(AAssetManager_fromJava(env, assetManager))
@@ -102,11 +102,8 @@ extern "C" JNIEXPORT void Java_emu_skyline_EmulationActivity_executeApplication(
         AudioWeak = os->state.audio;
         InputWeak = os->state.input;
         jvmManager->InitializeControllers();
-        env->ReleaseStringUTFChars(appFilesPathJstring, appFilesPath);
 
-        auto romUri{env->GetStringUTFChars(romUriJstring, nullptr)};
+        logger->InfoNoPrefix("Launching ROM {}", skyline::JniString(env, romUriJstring));
-        logger->InfoNoPrefix("Launching ROM {}", romUri);
-        env->ReleaseStringUTFChars(romUriJstring, romUri);
 
         os->Execute(romFd, static_cast<skyline::loader::RomFormat>(romType));
     } catch (std::exception &e) {

app/src/main/cpp/loader_jni.cpp

@@ -14,10 +14,7 @@
 extern "C" JNIEXPORT jint JNICALL Java_emu_skyline_loader_RomFile_populate(JNIEnv *env, jobject thiz, jint jformat, jint fd, jstring appFilesPathJstring, jint systemLanguage) {
     skyline::loader::RomFormat format{static_cast<skyline::loader::RomFormat>(jformat)};
 
-    auto appFilesPath{env->GetStringUTFChars(appFilesPathJstring, nullptr)};
+    auto keyStore{std::make_shared<skyline::crypto::KeyStore>(skyline::JniString(env, appFilesPathJstring))};
-    auto keyStore{std::make_shared<skyline::crypto::KeyStore>(appFilesPath)};
-    env->ReleaseStringUTFChars(appFilesPathJstring, appFilesPath);
-
     std::unique_ptr<skyline::loader::Loader> loader;
     try {
         auto backing{std::make_shared<skyline::vfs::OsBacking>(fd)};

app/src/main/cpp/skyline/jvm.cpp

@@ -4,6 +4,13 @@
 #include "jvm.h"
 
 namespace skyline {
+    std::string JniString::GetJString(JNIEnv *env, jstring jString) {
+        auto utf{env->GetStringUTFChars(jString, nullptr)};
+        std::string string{utf};
+        env->ReleaseStringUTFChars(jString, utf);
+        return string;
+    }
+
     /*
      * @brief A thread-local wrapper over JNIEnv and JavaVM which automatically handles attaching and detaching threads
      */

app/src/main/cpp/skyline/jvm.h

@@ -7,6 +7,17 @@
 #include <jni.h>
 
 namespace skyline {
+    /**
+     * @brief A wrapper over std::string that supports construction using a JNI jstring
+     */
+    class JniString : public std::string {
+      private:
+        static std::string GetJString(JNIEnv *env, jstring jString);
+
+      public:
+        JniString(JNIEnv *env, jstring jString) : std::string(GetJString(env, jString)) {}
+    };
+
     /**
      * @brief The JvmManager class is used to simplify transactions with the Java component
      */