rust: Create separate high-level struct instead of wrapping FFI

bindings/rust/evmc-vm/src/lib.rs

@@ -6,8 +6,52 @@ pub use evmc_sys as ffi;
 // TODO: Add a derive macro here for creating evmc_create
 
 /// EVMC result structure.
-pub struct ExecutionResult(Box<ffi::evmc_result>);
+pub struct ExecutionResult {
+    status: ffi::evmc_status_code,
+    gas: i64,
+    output: Option<Vec<u8>>,
+    release_fn: Option<unsafe extern "C" fn(*const ffi::evmc_result)>,
+    create_addr: Option<ffi::evmc_address>,
+}
 
+impl From<ffi::evmc_result> for ExecutionResult {
+    fn from(result: ffi::evmc_result) -> Self {
+        let ret = ExecutionResult {
+            status: result.status_code.clone(), // Maybe explicit copying not needed?
+            gas: result.gas_left.clone(),
+            output: if !result.output_data.is_null() {
+                // Pre-allocate a vector.
+                let mut buf: Vec<u8> = Vec::with_capacity(result.output_size);
+
+                // Copy from the C struct's buffer to the vec's buffer.
+                unsafe {
+                    std::ptr::copy(result.output_data, buf.as_mut_ptr(), result.output_size);
+                }
+
+                Some(buf)
+            } else {
+                None
+            },
+            release_fn: result.release.clone(),
+            create_addr: if result.status_code == ffi::evmc_status_code::EVMC_SUCCESS {
+                // NOTE: This field is only Some if the evmc return code is SUCCESS.
+                Some(result.create_address)
+            } else {
+                None
+            },
+        };
+
+        // Release allocated ffi struct.
+        unsafe {
+            result.release.unwrap()(&result as *const ffi::evmc_result);
+        }
+
+        ret
+    }
+
+}
+
+/*
 impl ExecutionResult {
     /// Initialize a new result struct given a status code, remaining gas, and optional output
     /// data.
@@ -74,7 +118,7 @@ impl ExecutionResult {
         unsafe { ExecutionResult::from_boxed(Box::from_raw(raw)) }
     }
 }
-
+*/
 /// Callback to pass across FFI, de-allocating the struct.
 extern "C" fn release_result(result: *const ffi::evmc_result) {
     unsafe {
@@ -86,7 +130,7 @@ extern "C" fn release_result(result: *const ffi::evmc_result) {
 mod tests {
     use super::*;
     use evmc_sys as ffi;
-
+/*
     #[test]
     fn constructor() {
         let result = ExecutionResult::new(
@@ -132,4 +176,5 @@ mod tests {
         assert!(back.output().unwrap().len() == 4);
         assert!(back.output().unwrap() == &[0xde, 0xad, 0xbe, 0xef]);
     }
+*/
 }