EVM-C: Add examples of evm_result usages

examples/CMakeLists.txt

@@ -1,8 +1,8 @@
-add_compile_options("-Wno-extra")  # Override -Wextra, I don't know better option.
-
 add_library(example-vm STATIC examplevm.c)
 target_include_directories(example-vm PRIVATE ../include)
+target_compile_options(example-vm PRIVATE -Wno-extra)
 
 add_executable(example-capi capi.c)
 target_include_directories(example-capi PRIVATE ../include)
 target_link_libraries(example-capi PRIVATE example-vm)
+target_compile_options(example-capi PRIVATE -Wno-extra)

examples/examplevm.c

@@ -32,6 +32,11 @@ static void evm_release_result(struct evm_result const* result)
 {
 }
 
+static void free_result_output_data(struct evm_result const* result)
+{
+    free((uint8_t*)result->output_data);
+}
+
 static struct evm_result evm_execute(struct evm_instance* instance,
                                      struct evm_env* env,
                                      enum evm_mode mode,
@@ -44,8 +49,36 @@ static struct evm_result evm_execute(struct evm_instance* instance,
                                      struct evm_uint256be value)
 {
     struct evm_result ret = {};
+    if (code_size == 0) {
+        // In case of empty code return a fancy error message.
+        const char* msg = mode == EVM_METROPOLIS ?
+                          "Welcome to Metropolis!" : "Hello Ethereum!";
+        ret.output_data = (const uint8_t*)msg;
+        ret.output_size = strlen(msg);
+        ret.code = EVM_FAILURE;
+        ret.release = NULL;  // We don't need to release the constant messages.
+        return ret;
+    }
 
-    // Execute code and refer to callbacks: instance->query_fn()
+    struct examplevm* vm = (struct examplevm*)instance;
+
+    // Simulate executing the answering some questions from the code.
+
+    const char my_address_question[] = "What is my address?";
+    if (code_size == strlen(my_address_question) &&
+        strncmp((const char*)code, my_address_question, code_size)) {
+        union evm_variant query_result;
+        vm->query_fn(&query_result, env, EVM_ADDRESS, NULL);
+        static const size_t address_size = sizeof(query_result.address);
+        uint8_t* output_data = (uint8_t*)malloc(address_size);
+        memcpy(output_data, &query_result.address, address_size);
+        ret.code = EVM_SUCCESS;
+        ret.output_data = output_data;
+        ret.output_size = address_size;
+        ret.release = &free_result_output_data;
+        ret.internal_memory = NULL; // We don't need another pointer.
+        return ret;
+    }
 
     ret.release = evm_release_result;
     ret.code = EVM_FAILURE;