loader: Make error_code in evmc_load_and_create() optional

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 - Changed: [[#293](https://github.com/ethereum/evmc/pull/293)]
   In C++ API `evmc::result::raw()` renamed to `evmc::result::release_raw()`.
+- Changed: [[#311](https://github.com/ethereum/evmc/pull/311)]
+  In `evmc_load_and_create()` the `error_code` is optional (can be `NULL`).
 - Fixed:
   [[#261](https://github.com/ethereum/evmc/issues/261),
   [#263](https://github.com/ethereum/evmc/pull/263)]

include/evmc/loader.h

@@ -44,10 +44,10 @@ enum evmc_loader_error_code
 };
 
 /**
- * Dynamically loads the shared object (DLL) with an EVM implementation.
+ * Dynamically loads the EVMC module with a VM implementation.
  *
- * This function tries to open a DLL at the given `filename`. On UNIX-like systems dlopen() function
- * is used. On Windows LoadLibrary() function is used.
+ * This function tries to open a dynamically loaded library (DLL) at the given `filename`.
+ * On UNIX-like systems dlopen() function is used. On Windows LoadLibrary() function is used.
  *
  * If the file does not exist or is not a valid shared library the ::EVMC_LOADER_CANNOT_OPEN error
  * code is signaled and NULL is returned.
@@ -77,28 +77,36 @@ enum evmc_loader_error_code
  * It is safe to call this function with the same filename argument multiple times
  * (the DLL is not going to be loaded multiple times).
  *
- * @param filename    The null terminated path (absolute or relative) to the shared library
- *                    containing the EVM implementation. If the value is NULL, an empty C-string
- *                    or longer than the path maximum length the ::EVMC_LOADER_INVALID_ARGUMENT is
- *                    signaled.
+ * @param filename    The null terminated path (absolute or relative) to an EVMC module
+ *                    (dynamically loaded library) containing the VM implementation.
+ *                    If the value is NULL, an empty C-string or longer than the path maximum length
+ *                    the ::EVMC_LOADER_INVALID_ARGUMENT is signaled.
  * @param error_code  The pointer to the error code. If not NULL the value is set to
  *                    ::EVMC_LOADER_SUCCESS on success or any other error code as described above.
- * @return            The pointer to the EVM create function or NULL.
+ * @return            The pointer to the EVM create function or NULL in case of error.
  */
 evmc_create_fn evmc_load(const char* filename, enum evmc_loader_error_code* error_code);
 
 /**
- * Dynamically loads the VM DLL and creates the VM instance.
+ * Dynamically loads the EVMC module and creates the VM instance.
  *
  * This is a macro for creating the VM instance with the function returned from evmc_load().
  * The function signals the same errors as evmc_load() and additionally:
- *  - ::EVMC_LOADER_INSTANCE_CREATION_FAILURE when the create function returns NULL,
- *  - ::EVMC_LOADER_ABI_VERSION_MISMATCH when the created VM instance has ABI version different
- *  from the ABI version of this library (::EVMC_ABI_VERSION).
+ * - ::EVMC_LOADER_INSTANCE_CREATION_FAILURE when the create function returns NULL,
+ * - ::EVMC_LOADER_ABI_VERSION_MISMATCH when the created VM instance has ABI version different
+ *   from the ABI version of this library (::EVMC_ABI_VERSION).
  *
  * It is safe to call this function with the same filename argument multiple times:
  * the DLL is not going to be loaded multiple times, but the function will return new VM instance
  * each time.
+ *
+ * @param filename    The null terminated path (absolute or relative) to an EVMC module
+ *                    (dynamically loaded library) containing the VM implementation.
+ *                    If the value is NULL, an empty C-string or longer than the path maximum length
+ *                    the ::EVMC_LOADER_INVALID_ARGUMENT is signaled.
+ * @param error_code  The pointer to the error code. If not NULL the value is set to
+ *                    ::EVMC_LOADER_SUCCESS on success or any other error code as described above.
+ * @return            The pointer to the created VM or NULL in case of error.
  */
 struct evmc_instance* evmc_load_and_create(const char* filename,
                                            enum evmc_loader_error_code* error_code);

lib/loader/loader.c

@@ -212,22 +212,29 @@ struct evmc_instance* evmc_load_and_create(const char* filename,
     if (!create_fn)
         return NULL;
 
+    enum evmc_loader_error_code ec = EVMC_LOADER_SUCCESS;
+
     struct evmc_instance* instance = create_fn();
     if (!instance)
     {
-        *error_code = set_error(EVMC_LOADER_INSTANCE_CREATION_FAILURE,
-                                "creating EVMC instance of %s has failed", filename);
-        return NULL;
+        ec = set_error(EVMC_LOADER_INSTANCE_CREATION_FAILURE,
+                       "creating EVMC instance of %s has failed", filename);
+        goto exit;
     }
 
     if (!evmc_is_abi_compatible(instance))
     {
+        ec = set_error(EVMC_LOADER_ABI_VERSION_MISMATCH,
+                       "EVMC ABI version %d of %s mismatches the expected version %d",
+                       instance->abi_version, filename, EVMC_ABI_VERSION);
         evmc_destroy(instance);
-        *error_code = set_error(EVMC_LOADER_ABI_VERSION_MISMATCH,
-                                "EVMC ABI version %d of %s mismatches the expected version %d",
-                                instance->abi_version, filename, EVMC_ABI_VERSION);
-        return NULL;
+        instance = NULL;
+        goto exit;
     }
 
+exit:
+    if (error_code)
+        *error_code = ec;
+
     return instance;
 }

test/unittests/test_loader.cpp

@@ -301,6 +301,11 @@ TEST_F(loader, load_and_create_failure)
     EXPECT_TRUE(vm == nullptr);
     EXPECT_EQ(ec, EVMC_LOADER_INSTANCE_CREATION_FAILURE);
     EXPECT_STREQ(evmc_last_error_msg(), "creating EVMC instance of failure.vm has failed");
+    EXPECT_TRUE(evmc_last_error_msg() == nullptr);
+
+    vm = evmc_load_and_create(evmc_test_library_path, nullptr);
+    EXPECT_TRUE(vm == nullptr);
+    EXPECT_STREQ(evmc_last_error_msg(), "creating EVMC instance of failure.vm has failed");
 }
 
 TEST_F(loader, load_and_create_abi_mismatch)
@@ -315,5 +320,11 @@ TEST_F(loader, load_and_create_abi_mismatch)
         "EVMC ABI version 1985 of abi1985.vm mismatches the expected version " +
         std::to_string(EVMC_ABI_VERSION);
     EXPECT_EQ(evmc_last_error_msg(), expected_error_msg);
+    EXPECT_TRUE(evmc_last_error_msg() == nullptr);
+    EXPECT_EQ(destroy_count, create_count);
+
+    vm = evmc_load_and_create(evmc_test_library_path, nullptr);
+    EXPECT_TRUE(vm == nullptr);
+    EXPECT_EQ(evmc_last_error_msg(), expected_error_msg);
     EXPECT_EQ(destroy_count, create_count);
 }