encryptMessage : the UTF8 conversion is done on JAVA side.

java/android/OlmLibSdk/olm-sdk/src/main/java/org/matrix/olm/OlmOutboundGroupSession.java

@@ -235,12 +235,16 @@ public class OlmOutboundGroupSession extends CommonSerializeUtils implements Ser
         String retValue = null;
 
         if(!TextUtils.isEmpty(aClearMsg)) {
-            retValue = encryptMessageJni(aClearMsg);
+            try {
+                retValue = encryptMessageJni(aClearMsg.getBytes("UTF-8"));
+            } catch (Exception e) {
+                Log.e(LOG_TAG, "## encryptMessage() failed " + e.getMessage());
+            }
         }
 
         return retValue;
     }
-    private native String encryptMessageJni(String aClearMsg);
+    private native String encryptMessageJni(byte[] aClearMsgBuffer);
 
     /**
      * Return true the object resources have been released.<br>

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.cpp

@@ -262,30 +262,30 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env
 }
 
 
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jstring aClearMsg)
+JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsgBuffer)
 {
     LOGD("## encryptMessageJni(): IN");
 
     jstring encryptedMsgRetValue = 0;
     OlmOutboundGroupSession *sessionPtr = NULL;
-    const char *clearMsgPtr = NULL;
+    jbyte* clearMsgPtr = NULL;
 
     if (!(sessionPtr = (OlmOutboundGroupSession*)getOutboundGroupSessionInstanceId(env,thiz)))
     {
         LOGE(" ## encryptMessageJni(): failure - invalid outbound group session ptr=NULL");
     }
-    else if (!aClearMsg)
+    else if (!aClearMsgBuffer)
     {
         LOGE(" ## encryptMessageJni(): failure - invalid clear message");
     }
-    else if (!(clearMsgPtr = env->GetStringUTFChars(aClearMsg, 0)))
+    else if (!(clearMsgPtr = env->GetByteArrayElements(aClearMsgBuffer, NULL)))
     {
         LOGE(" ## encryptMessageJni(): failure - clear message JNI allocation OOM");
     }
     else
     {
         // get clear message length
-        size_t clearMsgLength = (size_t)env->GetStringUTFLength(aClearMsg);
+        size_t clearMsgLength = (size_t)env->GetArrayLength(aClearMsgBuffer);
         LOGD(" ## encryptMessageJni(): clearMsgLength=%lu",static_cast<long unsigned int>(clearMsgLength));
 
         // compute max encrypted length
@@ -325,7 +325,7 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv
     // free alloc
     if (clearMsgPtr)
     {
-        env->ReleaseStringUTFChars(aClearMsg, clearMsgPtr);
+        env->ReleaseByteArrayElements(aClearMsgBuffer, clearMsgPtr, JNI_ABORT);
     }
 
     return encryptedMsgRetValue;

java/android/OlmLibSdk/olm-sdk/src/main/jni/olm_outbound_group_session.h

@@ -37,7 +37,7 @@ JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionIdentifierJni)(JNIE
 JNIEXPORT jint OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(messageIndexJni)(JNIEnv *env, jobject thiz);
 JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(sessionKeyJni)(JNIEnv *env, jobject thiz);
 
-JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jstring aClearMsgPtr);
+JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(encryptMessageJni)(JNIEnv *env, jobject thiz, jbyteArray aClearMsgBuffer);
 
 // serialization
 JNIEXPORT jstring OLM_OUTBOUND_GROUP_SESSION_FUNC_DEF(serializeDataWithKeyJni)(JNIEnv *env, jobject thiz, jstring aKey, jobject aErrorMsg);