Add foundational emscripten functions and types to C API

lib/runtime-c-api/src/import/emscripten.rs

@@ -0,0 +1,58 @@
+//! Functions and types for dealing with Emscripten imports
+
+use super::*;
+use crate::module::wasmer_module_t;
+use std::ptr;
+use wasmer_emscripten::EmscriptenGlobals;
+use wasmer_runtime::Module;
+
+/// Type used to construct an import_object_t with Emscripten imports.
+#[repr(C)]
+pub struct wasmer_emscripten_globals_t;
+
+/// Create a `wasmer_emscripten_globals_t` from a Wasm module.
+#[no_mangle]
+pub unsafe extern "C" fn wasmer_emscripten_get_emscripten_globals(
+    module: *const wasmer_module_t,
+) -> *mut wasmer_emscripten_globals_t {
+    if module.is_null() {
+        return ptr::null_mut();
+    }
+    let module = &*(module as *const Module);
+    match EmscriptenGlobals::new(module) {
+        Ok(globals) => Box::into_raw(Box::new(globals)) as *mut wasmer_emscripten_globals_t,
+        Err(msg) => {
+            update_last_error(CApiError { msg });
+            return ptr::null_mut();
+        }
+    }
+}
+
+/// Destroy `wasmer_emscrpten_globals_t` created by
+/// `wasmer_emscripten_get_emscripten_globals`.
+#[no_mangle]
+pub unsafe extern "C" fn wasmer_emscripten_destroy_emscripten_globals(
+    globals: *mut wasmer_emscripten_globals_t,
+) {
+    if globals.is_null() {
+        return;
+    }
+    let _ = Box::from_raw(globals);
+}
+
+/// Create a `wasmer_import_object_t` with Emscripten imports, use
+/// `wasmer_emscripten_get_emscripten_globals` to get a
+/// `wasmer_emscripten_globals_t` from a `wasmer_module_t`.
+#[no_mangle]
+pub unsafe extern "C" fn wasmer_emscripten_generate_import_object(
+    globals: *mut wasmer_emscripten_globals_t,
+) -> *mut wasmer_import_object_t {
+    if globals.is_null() {
+        return ptr::null_mut();
+    }
+    // TODO: figure out if we should be using UnsafeCell here or something
+    let g = &mut *(globals as *mut EmscriptenGlobals);
+    let import_object = Box::new(wasmer_emscripten::generate_emscripten_env(g));
+
+    Box::into_raw(import_object) as *mut wasmer_import_object_t
+}