java: add CopyFromBuffer helper and ensure the properly sized ByteBuf…

…fer is used

bindings/java/c/host.c

@@ -5,6 +5,7 @@
 
 #include <assert.h>
 #include <stdlib.h>
+#include <string.h>
 
 #include "host.h"
 
@@ -34,6 +35,20 @@ static jbyteArray CopyDataToJava(JNIEnv* jenv, const void* ptr, size_t size)
     return ret;
 }
 
+static void CopyFromByteBuffer(JNIEnv* jenv, jobject src, void* dst, size_t size)
+{
+    size_t src_size = (size_t)(*jenv)->GetDirectBufferCapacity(jenv, src);
+    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);
+}
+
 static bool account_exists_fn(struct evmc_host_context* context, const evmc_address* address)
 {
     const char java_method_name[] = "account_exists";
@@ -87,11 +102,10 @@ static evmc_bytes32 get_storage_fn(struct evmc_host_context* context,
     // call java method
     jobject jresult =
         (*jenv)->CallStaticObjectMethod(jenv, host_class, method, (jobject)context, jaddress, jkey);
-
     assert(jresult != NULL);
-    evmc_bytes32* result_ptr = (struct evmc_bytes32*)(*jenv)->GetDirectBufferAddress(jenv, jresult);
-    assert(result_ptr != NULL);
-    return *result_ptr;  // copy here
+    struct evmc_bytes32 result;
+    CopyFromByteBuffer(jenv, jresult, &result, sizeof(struct evmc_bytes32));
+    return result;
 }
 
 static enum evmc_storage_status set_storage_fn(struct evmc_host_context* context,
@@ -149,10 +163,8 @@ static evmc_uint256be get_balance_fn(struct evmc_host_context* context, const ev
     jobject jresult =
         (*jenv)->CallStaticObjectMethod(jenv, host_class, method, (jobject)context, jaddress);
     assert(jresult != NULL);
-
-    evmc_uint256be* result_ptr = (evmc_uint256be*)(*jenv)->GetDirectBufferAddress(jenv, jresult);
-    assert(result_ptr != NULL);
-    evmc_uint256be result = *result_ptr;  // copy here
+    evmc_uint256be result;
+    CopyFromByteBuffer(jenv, jresult, &result, sizeof(evmc_uint256be));
 
     (*jenv)->ReleaseByteArrayElements(jenv, jaddress, (jbyte*)address, 0);
 
@@ -209,10 +221,8 @@ static evmc_bytes32 get_code_hash_fn(struct evmc_host_context* context, const ev
     jobject jresult =
         (*jenv)->CallStaticObjectMethod(jenv, host_class, method, (jobject)context, jaddress);
     assert(jresult != NULL);
-
-    evmc_bytes32* result_ptr = (struct evmc_bytes32*)(*jenv)->GetDirectBufferAddress(jenv, jresult);
-    assert(result_ptr != NULL);
-    evmc_bytes32 result = *result_ptr;  // copy here
+    struct evmc_bytes32 result;
+    CopyFromByteBuffer(jenv, jresult, &result, sizeof(struct evmc_bytes32));
 
     (*jenv)->ReleaseByteArrayElements(jenv, jaddress, (jbyte*)address, 0);
 
@@ -317,11 +327,9 @@ static struct evmc_result call_fn(struct evmc_host_context* context, const struc
     jobject jresult =
         (*jenv)->CallStaticObjectMethod(jenv, host_class, method, (jobject)context, jmsg);
     assert(jresult != NULL);
-
-    struct evmc_result* result_ptr =
-        (struct evmc_result*)(*jenv)->GetDirectBufferAddress(jenv, jresult);
-    assert(result_ptr != NULL);
-    return *result_ptr;  // copy here
+    struct evmc_result result;
+    CopyFromByteBuffer(jenv, jresult, &result, sizeof(struct evmc_result));
+    return result;
 }
 
 static struct evmc_tx_context get_tx_context_fn(struct evmc_host_context* context)
@@ -345,10 +353,9 @@ static struct evmc_tx_context get_tx_context_fn(struct evmc_host_context* contex
     jobject jresult = (*jenv)->CallStaticObjectMethod(jenv, host_class, method, (jobject)context);
     assert(jresult != NULL);
 
-    struct evmc_tx_context* result_ptr =
-        (struct evmc_tx_context*)(*jenv)->GetDirectBufferAddress(jenv, jresult);
-    assert(result_ptr != NULL);
-    return *result_ptr;  // copy here
+    struct evmc_tx_context result;
+    CopyFromByteBuffer(jenv, jresult, &result, sizeof(struct evmc_tx_context));
+    return result;
 }
 
 static evmc_bytes32 get_block_hash_fn(struct evmc_host_context* context, int64_t number)
@@ -373,9 +380,9 @@ static evmc_bytes32 get_block_hash_fn(struct evmc_host_context* context, int64_t
         (*jenv)->CallStaticObjectMethod(jenv, host_class, method, (jobject)context, (jlong)number);
     assert(jresult != NULL);
 
-    evmc_bytes32* result_ptr = (struct evmc_bytes32*)(*jenv)->GetDirectBufferAddress(jenv, jresult);
-    assert(result_ptr != NULL);
-    return *result_ptr;  // copy here
+    struct evmc_bytes32 result;
+    CopyFromByteBuffer(jenv, jresult, &result, sizeof(struct evmc_bytes32));
+    return result;
 }
 
 static void emit_log_fn(struct evmc_host_context* context,