example: Implement proper Rust VM example

examples/example-rust-vm/src/lib.rs

@@ -1,6 +1,52 @@
 extern crate evmc_vm;
 
+use evmc_vm::evmc_sys as ffi;
+
+extern "C" fn execute(
+    instance: *mut ffi::evmc_instance,
+    context: *mut ffi::evmc_context,
+    rev: ffi::evmc_revision,
+    msg: *const ffi::evmc_message,
+    code: *const u8,
+    code_size: usize,
+) -> ffi::evmc_result {
+    let result = evmc_vm::ExecutionResult::new(
+        ffi::evmc_status_code::EVMC_SUCCESS,
+        66,
+        None,
+        ffi::evmc_address { bytes: [0u8; 20] },
+    );
+    result.into()
+}
+
+extern "C" fn get_capabilities(
+    instance: *mut ffi::evmc_instance,
+) -> ffi::evmc_capabilities_flagset {
+    ffi::evmc_capabilities::EVMC_CAPABILITY_EVM1 as u32
+}
+
+extern "C" fn destroy(instance: *mut ffi::evmc_instance) {
+    drop(unsafe { Box::from_raw(instance) })
+}
+
 #[no_mangle]
-pub extern "C" fn evmc_create_examplerustvm() -> *const evmc_vm::ffi::evmc_instance {
-    std::ptr::null()
+pub extern "C" fn evmc_create_examplerustvm() -> *const ffi::evmc_instance {
+    let ret = ffi::evmc_instance {
+        abi_version: ffi::EVMC_ABI_VERSION as i32,
+        destroy: Some(destroy),
+        execute: Some(execute),
+        get_capabilities: Some(get_capabilities),
+        set_option: None,
+        set_tracer: None,
+        name: {
+            let c_str =
+                std::ffi::CString::new("ExampleRustVM").expect("Failed to build EVMC name string");
+            c_str.into_raw() as *const i8
+        },
+        version: {
+            let c_str = std::ffi::CString::new("1.0").expect("Failed to build EVMC version string");
+            c_str.into_raw() as *const i8
+        },
+    };
+    Box::into_raw(Box::new(ret))
 }