wasmer/lib/emscripten/src/varargs.rs

use std::mem;
use wasmer_runtime_core::{types::WasmExternType, vm::Ctx};
// use std::ffi::CStr;
use std::os::raw::c_char;

#[repr(transparent)]
#[derive(Copy, Clone)]
pub struct VarArgs {
    pub pointer: u32, // assuming 32bit wasm
}

impl VarArgs {
    pub fn get<T: Sized>(&mut self, ctx: &mut Ctx) -> T {
        let ptr = emscripten_memory_pointer!(ctx.memory(0), self.pointer);
        self.pointer += mem::size_of::<T>() as u32;
        unsafe { (ptr as *const T).read() }
    }

    // pub fn getStr<'a>(&mut self, ctx: &mut Ctx) -> &'a CStr {
    pub fn get_str(&mut self, ctx: &mut Ctx) -> *const c_char {
        let ptr_addr: u32 = self.get(ctx);
        let ptr = emscripten_memory_pointer!(ctx.memory(0), ptr_addr) as *const c_char;
        ptr
        // unsafe { CStr::from_ptr(ptr) }
    }
}

unsafe impl WasmExternType for VarArgs {
    type Native = i32;

    fn to_native(self) -> Self::Native {
        self.pointer as _
    }
    fn from_native(n: Self::Native) -> Self {
        Self { pointer: n as u32 }
    }
}