Update Emscripten API layout; expose inner parts to to C API; add test

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

@@ -1,10 +1,11 @@
 //! Functions and types for dealing with Emscripten imports
 
 use super::*;
-use crate::module::wasmer_module_t;
+use crate::{get_slice_checked, instance::wasmer_instance_t, module::wasmer_module_t};
+
 use std::ptr;
 use wasmer_emscripten::EmscriptenGlobals;
-use wasmer_runtime::Module;
+use wasmer_runtime::{Instance, Module};
 
 /// Type used to construct an import_object_t with Emscripten imports.
 #[repr(C)]
@@ -40,9 +41,88 @@ pub unsafe extern "C" fn wasmer_emscripten_destroy_emscripten_globals(
     let _ = Box::from_raw(globals);
 }
 
+/// Execute global constructors (required if the module is compiled from C++)
+/// and sets up the internal environment.
+///
+/// This function sets the data pointer in the same way that
+/// [`wasmer_instance_context_data_set`] does.
+#[no_mangle]
+pub unsafe extern "C" fn wasmer_emscripten_set_up_emscripten(
+    instance: *mut wasmer_instance_t,
+    globals: *mut wasmer_emscripten_globals_t,
+) -> wasmer_result_t {
+    if globals.is_null() || instance.is_null() {
+        return wasmer_result_t::WASMER_ERROR;
+    }
+    let instance = &mut *(instance as *mut Instance);
+    instance.context_mut().data = globals as *mut c_void;
+    match wasmer_emscripten::set_up_emscripten(instance) {
+        Ok(_) => wasmer_result_t::WASMER_OK,
+        Err(e) => {
+            update_last_error(e);
+            wasmer_result_t::WASMER_ERROR
+        }
+    }
+}
+
+/// Convenience function for setting up arguments and calling the Emscripten
+/// main function.
+///
+/// WARNING:
+///
+/// Do not call this function on untrusted code when operating without
+/// additional sandboxing in place.
+/// Emscripten has access to many host system calls and therefore may do very
+/// bad things.
+#[no_mangle]
+pub unsafe extern "C" fn wasmer_emscripten_call_main(
+    instance: *mut wasmer_instance_t,
+    args: *const wasmer_byte_array,
+    args_len: c_uint,
+) -> wasmer_result_t {
+    if instance.is_null() || args.is_null() {
+        return wasmer_result_t::WASMER_ERROR;
+    }
+    let instance = &mut *(instance as *mut Instance);
+
+    let arg_list = get_slice_checked(args, args_len as usize);
+    let arg_process_result: Result<Vec<&str>, _> =
+        arg_list.iter().map(|arg| arg.as_str()).collect();
+    let arg_vec = match arg_process_result.as_ref() {
+        Ok(arg_vec) => arg_vec,
+        Err(err) => {
+            update_last_error(*err);
+            return wasmer_result_t::WASMER_ERROR;
+        }
+    };
+
+    let prog_name = if let Some(prog_name) = arg_vec.first() {
+        prog_name
+    } else {
+        update_last_error(CApiError {
+            msg: "First argument (program name) is required to execute Emscripten's main function"
+                .to_string(),
+        });
+        return wasmer_result_t::WASMER_ERROR;
+    };
+
+    match wasmer_emscripten::emscripten_call_main(instance, prog_name, &arg_vec[1..]) {
+        Ok(_) => wasmer_result_t::WASMER_OK,
+        Err(e) => {
+            update_last_error(e);
+            wasmer_result_t::WASMER_ERROR
+        }
+    }
+}
+
 /// 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`.
+///
+/// WARNING:
+///1
+/// This `import_object_t` contains thin-wrappers around host system calls.
+/// Do not use this to execute untrusted code without additional sandboxing.
 #[no_mangle]
 pub unsafe extern "C" fn wasmer_emscripten_generate_import_object(
     globals: *mut wasmer_emscripten_globals_t,