android: Use correct encoding when converting strings

The JNI functions that have "UTF" their name use "modified UTF-8"
rather than the standard UTF-8 that Citra uses, at least according
to Oracle's documentation, so it is incorrect for us to use them.
This change fixes the problem by converting between UTF-8 and
UTF-16 manually instead of letting JNI do it for us.

src/android/app/src/main/jni/android_common/android_common.cpp

@@ -5,20 +5,28 @@
 #include "jni/android_common/android_common.h"
 
 #include <string>
+#include <string_view>
 
 #include <jni.h>
 
-std::string GetJString(JNIEnv *env, jstring jstr) {
+#include "common/string_util.h"
+
+std::string GetJString(JNIEnv* env, jstring jstr) {
     if (!jstr) {
         return {};
     }
 
-    const char *s = env->GetStringUTFChars(jstr, nullptr);
-    std::string result = s;
-    env->ReleaseStringUTFChars(jstr, s);
-    return result;
+    const jchar* jchars = env->GetStringChars(jstr, nullptr);
+    const jsize length = env->GetStringLength(jstr);
+    const std::u16string_view string_view(reinterpret_cast<const char16_t*>(jchars), length);
+    const std::string converted_string = Common::UTF16ToUTF8(string_view);
+    env->ReleaseStringChars(jstr, jchars);
+
+    return converted_string;
 }
 
-jstring ToJString(JNIEnv* env, const std::string& str) {
-    return env->NewStringUTF(str.c_str());
+jstring ToJString(JNIEnv* env, std::string_view str) {
+    const std::u16string converted_string = Common::UTF8ToUTF16(str);
+    return env->NewString(reinterpret_cast<const jchar*>(converted_string.data()),
+                          static_cast<jint>(converted_string.size()));
 }

src/android/app/src/main/jni/android_common/android_common.h

@@ -9,4 +9,4 @@
 #include <jni.h>
 
 std::string GetJString(JNIEnv* env, jstring jstr);
-jstring ToJString(JNIEnv* env, const std::string& str);
+jstring ToJString(JNIEnv* env, std::string_view str);

src/common/string_util.cpp

@@ -8,6 +8,8 @@
 #include <cstdlib>
 #include <locale>
 #include <sstream>
+#include <string>
+#include <string_view>
 #include "common/common_paths.h"
 #include "common/logging/log.h"
 #include "common/string_util.h"
@@ -135,14 +137,14 @@ std::string ReplaceAll(std::string result, const std::string& src, const std::st
     return result;
 }
 
-std::string UTF16ToUTF8(const std::u16string& input) {
+std::string UTF16ToUTF8(std::u16string_view input) {
     std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert;
-    return convert.to_bytes(input);
+    return convert.to_bytes(input.data(), input.data() + input.size());
 }
 
-std::u16string UTF8ToUTF16(const std::string& input) {
+std::u16string UTF8ToUTF16(std::string_view input) {
     std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert;
-    return convert.from_bytes(input);
+    return convert.from_bytes(input.data(), input.data() + input.size());
 }
 
 #ifdef _WIN32

src/common/string_util.h

@@ -7,6 +7,7 @@
 #include <algorithm>
 #include <cstddef>
 #include <string>
+#include <string_view>
 #include <vector>
 #include "common/common_types.h"
 #include "common/swap.h"
@@ -37,8 +38,8 @@ void BuildCompleteFilename(std::string& _CompleteFilename, const std::string& _P
 [[nodiscard]] std::string ReplaceAll(std::string result, const std::string& src,
                                      const std::string& dest);
 
-[[nodiscard]] std::string UTF16ToUTF8(const std::u16string& input);
-[[nodiscard]] std::u16string UTF8ToUTF16(const std::string& input);
+[[nodiscard]] std::string UTF16ToUTF8(std::u16string_view input);
+[[nodiscard]] std::u16string UTF8ToUTF16(std::string_view input);
 
 #ifdef _WIN32
 [[nodiscard]] std::string UTF16ToUTF8(const std::wstring& input);