From a58216158b155038d1816d344175876d69b74a3d Mon Sep 17 00:00:00 2001
From: Ivan Enderlin <ivan@mnt.io>
Date: Fri, 18 Sep 2020 10:38:35 +0200
Subject: [PATCH] feat: Implement `Module`.

---
 wasmer/error.go  |  2 +-
 wasmer/module.go | 35 +++++++++++++++++++++++++++--------
 wasmer/store.go  |  1 -
 3 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/wasmer/error.go b/wasmer/error.go
index a60898de..a6f80709 100644
--- a/wasmer/error.go
+++ b/wasmer/error.go
@@ -29,7 +29,7 @@ func newError() *Error {
 	}
 
 	return &Error{
-		message: C.GoString(errorMessagePointer),
+		message: C.GoStringN(errorMessagePointer, errorLength),
 	}
 }
 
diff --git a/wasmer/module.go b/wasmer/module.go
index b5e9c594..97eafbbe 100644
--- a/wasmer/module.go
+++ b/wasmer/module.go
@@ -1,8 +1,22 @@
 package wasmer
 
 // #include <wasmer_wasm.h>
+//
+// // We can't create a `wasm_byte_vec_t` directly in Go otherwise cgo
+// // complains with “Go pointer to Go pointer”. The hack consists at
+// // creating the `wasm_byte_vec_t` directly in C.
+// own wasm_module_t* go_wasm_module_new(wasm_store_t *store, uint8_t *bytes, size_t bytes_length) {
+//     wasm_byte_vec_t wasm_bytes;
+//     wasm_bytes.size = bytes_length;
+//     wasm_bytes.data = (wasm_byte_t*) bytes;
+//
+//    return wasm_module_new(store, &wasm_bytes);
+// }
 import "C"
-import "unsafe"
+import (
+	"runtime"
+	"unsafe"
+)
 
 // A WebAssembly module contains stateless WebAssembly code that has
 // already been compiled and can be instantiated multiple times.
@@ -23,23 +37,28 @@ type Module struct {
 }
 
 func NewModule(store *Store, bytes []byte) (*Module, error) {
-	var bytes_ptr *C.char
+	var bytesPtr *C.uint8_t
 
 	if len(bytes) > 0 {
-		bytes_ptr = (*C.char)(unsafe.Pointer(&bytes[0]))
+		bytesPtr = (*C.uint8_t)(unsafe.Pointer(&bytes[0]))
 	}
 
-	var wasm_bytes C.wasm_byte_vec_t
-	wasm_bytes.size = C.size_t(len(bytes))
-	wasm_bytes.data = (*C.wasm_byte_t)(bytes_ptr)
-
 	module := &Module{
-		_inner: C.wasm_module_new(store.inner(), &wasm_bytes),
+		_inner: C.go_wasm_module_new(store.inner(), bytesPtr, C.size_t(len(bytes))),
 	}
 
+	runtime.KeepAlive(bytes)
+	runtime.SetFinalizer(module, func(module *Module) {
+		C.wasm_module_delete(module.inner())
+	})
+
 	if module == nil {
 		return nil, newError()
 	}
 
 	return module, nil
 }
+
+func (module *Module) inner() *C.wasm_module_t {
+	return module._inner
+}
diff --git a/wasmer/store.go b/wasmer/store.go
index 6959bc34..d78cb072 100644
--- a/wasmer/store.go
+++ b/wasmer/store.go
@@ -25,7 +25,6 @@ func NewStore(engine *Engine) *Store {
 		Engine: engine,
 	}
 
-	runtime.KeepAlive(engine)
 	runtime.SetFinalizer(store, func(store *Store) {
 		C.wasm_store_delete(store.inner())
 	})