java: introduce GetDirectBuffer helper

bindings/java/c/evmc-vm.c

@@ -95,9 +95,8 @@ JNIEXPORT void JNICALL Java_org_ethereum_evmc_EvmcVm_execute(JNIEnv* jenv,
     (void)jcls;
     struct evmc_message* msg = (struct evmc_message*)(*jenv)->GetDirectBufferAddress(jenv, jmsg);
     assert(msg != NULL);
-    size_t code_size = (size_t)(*jenv)->GetDirectBufferCapacity(jenv, jcode);
-    const uint8_t* code = (uint8_t*)(*jenv)->GetDirectBufferAddress(jenv, jcode);
-    assert(code != NULL);
+    size_t code_size;
+    const uint8_t* code = GetDirectBuffer(jenv, jcode, &code_size);
     struct evmc_host_context context = {jcontext_index};
     struct evmc_vm* evm = (struct evmc_vm*)(*jenv)->GetDirectBufferAddress(jenv, jevm);
     assert(evm != NULL);

bindings/java/c/host.c

@@ -37,15 +37,14 @@ static jbyteArray CopyDataToJava(JNIEnv* jenv, const void* ptr, size_t size)
 
 static void CopyFromByteBuffer(JNIEnv* jenv, jobject src, void* dst, size_t size)
 {
-    size_t src_size = (size_t)(*jenv)->GetDirectBufferCapacity(jenv, src);
+    size_t src_size;
+    const void* ptr = GetDirectBuffer(jenv, src, &src_size);
     if (src_size != size)
     {
         jclass exception_class = (*jenv)->FindClass(jenv, "java/lang/IllegalArgumentException");
         assert(exception_class != NULL);
         (*jenv)->ThrowNew(jenv, exception_class, "Unexpected length.");
     }
-    void* ptr = (*jenv)->GetDirectBufferAddress(jenv, src);
-    assert(ptr != NULL);
     memcpy(dst, ptr, size);
 }
 

bindings/java/c/host.h

@@ -19,6 +19,17 @@ struct evmc_host_context
 int evmc_java_set_jvm(JNIEnv*);
 const struct evmc_host_interface* evmc_java_get_host_interface();
 
+static inline void* GetDirectBuffer(JNIEnv* jenv, jobject buf, size_t* size)
+{
+    void* ret = (uint8_t*)(*jenv)->GetDirectBufferAddress(jenv, buf);
+    assert(ret != NULL);
+    jlong jsize = (*jenv)->GetDirectBufferCapacity(jenv, buf);
+    assert(jsize != -1);
+    if (size)
+        *size = (size_t)jsize;
+    return ret;
+}
+
 #ifdef __cplusplus
 }
 #endif