Fix memory leak in wat2wasm function

CHANGELOG.md

@@ -23,6 +23,7 @@
 
 ### Fixed
 
+- [#1855](https://github.com/wasmerio/wasmer/pull/1855) Fix memory leak when using `wat2wasm` in the C API, the function now takes its output parameter by pointer rather than returning an allocated `wasm_byte_vec_t`.
 - [#1841](https://github.com/wasmerio/wasmer/pull/1841) We will now panic when attempting to use a native function with a captured env as a host function. Previously this would silently do the wrong thing. See [#1840](https://github.com/wasmerio/wasmer/pull/1840) for info about Wasmer's support of closures as host functions.
 - [#1764](https://github.com/wasmerio/wasmer/pull/1764) Fix bug in WASI `path_rename` allowing renamed files to be 1 directory below a preopened directory.
 

lib/c-api/src/wasm_c_api/macros.rs

@@ -102,12 +102,13 @@ macro_rules! wasm_declare_vec {
 
 
             #[no_mangle]
-            pub unsafe extern "C" fn [<wasm_ $name _vec_delete>](ptr: *mut [<wasm_ $name _vec_t>]) {
-                let vec = &mut *ptr;
-                if !vec.data.is_null() {
-                    Vec::from_raw_parts(vec.data, vec.size, vec.size);
-                    vec.data = ::std::ptr::null_mut();
-                    vec.size = 0;
+            pub unsafe extern "C" fn [<wasm_ $name _vec_delete>](ptr: Option<&mut [<wasm_ $name _vec_t>]>) {
+                if let Some(vec) = ptr {
+                    if !vec.data.is_null() {
+                        Vec::from_raw_parts(vec.data, vec.size, vec.size);
+                        vec.data = ::std::ptr::null_mut();
+                        vec.size = 0;
+                    }
                 }
             }
         }

lib/c-api/src/wasm_c_api/wat.rs

@@ -6,11 +6,20 @@ use super::types::wasm_byte_vec_t;
 /// In case of failure, `wat2wasm` returns `NULL`.
 #[cfg(feature = "wat")]
 #[no_mangle]
-pub unsafe extern "C" fn wat2wasm(wat: &wasm_byte_vec_t) -> Option<Box<wasm_byte_vec_t>> {
-    let wat: &[u8] = wat.into_slice()?;
-    let result: wasm_byte_vec_t = c_try!(wasmer::wat2wasm(wat)).into_owned().into();
+pub unsafe extern "C" fn wat2wasm(wat: &wasm_byte_vec_t, out: &mut wasm_byte_vec_t) {
+    let wat: &[u8] = match wat.into_slice() {
+        Some(v) => v,
+        _ => return,
+    };
+    let result: wasm_byte_vec_t = match wasmer::wat2wasm(wat) {
+        Ok(val) => val.into_owned().into(),
+        Err(err) => {
+            crate::error::update_last_error(err);
+            return;
+        }
+    };
 
-    Some(Box::new(result))
+    *out = result;
 }
 
 #[cfg(test)]

lib/c-api/wasmer_wasm.h

@@ -239,6 +239,6 @@ int wasmer_last_error_message(char *buffer, int length);
  *
  * In case of failure, `wat2wasm` returns `NULL`.
  */
-wasm_byte_vec_t *wat2wasm(const wasm_byte_vec_t *wat);
+void wat2wasm(const wasm_byte_vec_t *wat, wasm_byte_vec_t *out);
 
 #endif /* WASMER_WASM_H */