C++ impl of export_key()

Makefile.conf

@@ -48,9 +48,9 @@ ifndef JAVA_HOME
 endif
 
 # Guessing USE_JAVAH
-# cant be guessed earlier, because we depend on JAVA_HOME which can be set in the local.conf
+# cant be guessed earlier, because it depends on JAVA_HOME which can be set in the local.conf
 # Old versions of a Java distribution have a `javah` binary, new version do not and the replacement is "javac -h"
-# TODO: dont check for presence of javah, but check if javac -h is supported, because some java (RHEL) has javah but supports javac -h
+# TODO: dont check for presence of javah, but check if javac -h is supported, because some java (RHEL) has javah but supports javac -h (and javac -h is preferred)
 ifndef USE_JAVAH
 	DUMMY:=$(shell which $(JAVA_HOME)/bin/javah)
 	ifeq ($(.SHELLSTATUS),0)
@@ -84,6 +84,7 @@ export YML_PATH=$(YML2_PATH)
 
 # BEGIN // kryptic hack to to replace a space with a newline
 # $(subst ${ },${space}, whatever)
+# maybe not well known: define/endef is custom makefile function definition
 null :=
 space := ${null} ${null}
 ${space} := ${space}

src/cxx/basic_api.cc

@@ -512,5 +512,32 @@ JNIEXPORT void JNICALL Java_foundation_pEp_jniadapter_Engine__1config_1passphras
     }
 }
 
+JNIEXPORT jbyteArray JNICALL Java_foundation_pEp_jniadapter_Engine__1export_1key (JNIEnv *env,
+        jobject obj,
+        jbyteArray fpr)
+{
+    std::mutex *mutex_local = nullptr;
+
+    {
+        std::lock_guard<std::mutex> l(global_mutex);
+        pEpLog("called with lock_guard");
+        mutex_local = get_engine_java_object_mutex(env, obj);
+    }
+    std::lock_guard<std::mutex> l(*mutex_local);
+
+    const char *_fpr = to_string(env, fpr);
+    char *buff = nullptr;
+    size_t size = 0;
+
+    PEP_STATUS status = passphraseWrap(::export_key, session(), _fpr, &buff, &size);
+
+    if (status != PEP_STATUS_OK) {
+        throw_pEp_Exception(env, status);
+        return NULL;
+    }
+
+    return from_string(env, buff);
+}
+
 } // extern "C"