denoland-deno/ext/ffi/lib.rs

// Copyright 2018-2022 the Deno authors. All rights reserved. MIT license.

use core::ptr::NonNull;
use deno_core::anyhow::anyhow;
use deno_core::error::generic_error;
use deno_core::error::range_error;
use deno_core::error::type_error;
use deno_core::error::AnyError;
use deno_core::futures::channel::mpsc;
use deno_core::futures::Future;
use deno_core::include_js_files;
use deno_core::op;
use deno_core::v8::fast_api;
use std::sync::mpsc::sync_channel;

use deno_core::serde_json::json;
use deno_core::serde_json::Value;
use deno_core::serde_v8;
use deno_core::v8;
use deno_core::Extension;
use deno_core::OpState;
use deno_core::Resource;
use deno_core::ResourceId;
use deno_core::ZeroCopyBuf;
use dlopen::raw::Library;
use libffi::middle::Arg;
use libffi::middle::Cif;
use libffi::raw::*;
use serde::Deserialize;
use serde::Serialize;
use std::borrow::Cow;
use std::cell::RefCell;
use std::collections::HashMap;
use std::ffi::c_void;
use std::ffi::CStr;
use std::os::raw::c_char;
use std::path::Path;
use std::path::PathBuf;
use std::ptr;
use std::rc::Rc;

#[cfg(not(target_os = "windows"))]
mod jit_trampoline;
#[cfg(not(target_os = "windows"))]
mod tcc;

thread_local! {
  static LOCAL_ISOLATE_POINTER: RefCell<*const v8::Isolate> = RefCell::new(ptr::null());
}

pub struct Unstable(pub bool);

fn check_unstable(state: &OpState, api_name: &str) {
  let unstable = state.borrow::<Unstable>();

  if !unstable.0 {
    eprintln!(
      "Unstable API '{}'. The --unstable flag must be provided.",
      api_name
    );
    std::process::exit(70);
  }
}

pub fn check_unstable2(state: &Rc<RefCell<OpState>>, api_name: &str) {
  let state = state.borrow();
  check_unstable(&state, api_name)
}

pub trait FfiPermissions {
  fn check(&mut self, path: Option<&Path>) -> Result<(), AnyError>;
}

#[derive(Clone)]
struct Symbol {
  cif: libffi::middle::Cif,
  ptr: libffi::middle::CodePtr,
  parameter_types: Vec<NativeType>,
  result_type: NativeType,
  // This is dead code only on Windows
  #[allow(dead_code)]
  can_callback: bool,
}

#[allow(clippy::non_send_fields_in_send_ty)]
unsafe impl Send for Symbol {}
unsafe impl Sync for Symbol {}

#[derive(Clone)]
struct PtrSymbol {
  cif: libffi::middle::Cif,
  ptr: libffi::middle::CodePtr,
}

impl PtrSymbol {
  fn new(fn_ptr: u64, def: &ForeignFunction) -> Self {
    let ptr = libffi::middle::CodePtr::from_ptr(fn_ptr as _);
    let cif = libffi::middle::Cif::new(
      def
        .parameters
        .clone()
        .into_iter()
        .map(libffi::middle::Type::from),
      def.result.into(),
    );

    Self { cif, ptr }
  }
}

#[allow(clippy::non_send_fields_in_send_ty)]
unsafe impl Send for PtrSymbol {}
unsafe impl Sync for PtrSymbol {}

struct DynamicLibraryResource {
  lib: Library,
  symbols: HashMap<String, Box<Symbol>>,
}

impl Resource for DynamicLibraryResource {
  fn name(&self) -> Cow<str> {
    "dynamicLibrary".into()
  }

  fn close(self: Rc<Self>) {
    drop(self)
  }
}

impl DynamicLibraryResource {
  fn get_static(&self, symbol: String) -> Result<*const c_void, AnyError> {
    // By default, Err returned by this function does not tell
    // which symbol wasn't exported. So we'll modify the error
    // message to include the name of symbol.
    //
    // SAFETY: The obtained T symbol is the size of a pointer.
    match unsafe { self.lib.symbol::<*const c_void>(&symbol) } {
      Ok(value) => Ok(Ok(value)),
      Err(err) => Err(generic_error(format!(
        "Failed to register symbol {}: {}",
        symbol, err
      ))),
    }?
  }
}

type PendingFfiAsyncWork = Box<dyn FnOnce()>;

struct FfiState {
  async_work_sender: mpsc::UnboundedSender<PendingFfiAsyncWork>,
  async_work_receiver: mpsc::UnboundedReceiver<PendingFfiAsyncWork>,
  active_refed_functions: usize,
}

pub fn init<P: FfiPermissions + 'static>(unstable: bool) -> Extension {
  Extension::builder()
    .js(include_js_files!(
      prefix "deno:ext/ffi",
      "00_ffi.js",
    ))
    .ops(vec![
      op_ffi_load::decl::<P>(),
      op_ffi_get_static::decl(),
      op_ffi_call_nonblocking::decl(),
      op_ffi_call_ptr::decl::<P>(),
      op_ffi_call_ptr_nonblocking::decl::<P>(),
      op_ffi_ptr_of::decl::<P>(),
      op_ffi_buf_copy_into::decl::<P>(),
      op_ffi_cstr_read::decl::<P>(),
      op_ffi_read_u8::decl::<P>(),
      op_ffi_read_i8::decl::<P>(),
      op_ffi_read_u16::decl::<P>(),
      op_ffi_read_i16::decl::<P>(),
      op_ffi_read_u32::decl::<P>(),
      op_ffi_read_i32::decl::<P>(),
      op_ffi_read_u64::decl::<P>(),
      op_ffi_read_f32::decl::<P>(),
      op_ffi_read_f64::decl::<P>(),
      op_ffi_unsafe_callback_create::decl::<P>(),
      op_ffi_unsafe_callback_ref::decl(),
    ])
    .event_loop_middleware(|op_state_rc, _cx| {
      // FFI callbacks coming in from other threads will call in and get queued.
      let mut maybe_scheduling = false;

      let mut work_items: Vec<PendingFfiAsyncWork> = vec![];

      {
        let mut op_state = op_state_rc.borrow_mut();
        let ffi_state = op_state.borrow_mut::<FfiState>();

        while let Ok(Some(async_work_fut)) =
          ffi_state.async_work_receiver.try_next()
        {
          // Move received items to a temporary vector so that we can drop the `op_state` borrow before we do the work.
          work_items.push(async_work_fut);
          maybe_scheduling = true;
        }

        if ffi_state.active_refed_functions > 0 {
          maybe_scheduling = true;
        }

        drop(op_state);
      }
      while let Some(async_work_fut) = work_items.pop() {
        async_work_fut();
      }

      maybe_scheduling
    })
    .state(move |state| {
      // Stolen from deno_webgpu, is there a better option?
      state.put(Unstable(unstable));

      let (async_work_sender, async_work_receiver) =
        mpsc::unbounded::<PendingFfiAsyncWork>();

      state.put(FfiState {
        active_refed_functions: 0,
        async_work_receiver,
        async_work_sender,
      });

      Ok(())
    })
    .build()
}

/// Defines the accepted types that can be used as
/// parameters and return values in FFI.
#[derive(Clone, Copy, Debug, Deserialize, Eq, PartialEq)]
#[serde(rename_all = "lowercase")]
enum NativeType {
  Void,
  U8,
  I8,
  U16,
  I16,
  U32,
  I32,
  U64,
  I64,
  USize,
  ISize,
  F32,
  F64,
  Pointer,
  Function,
}

impl From<NativeType> for libffi::middle::Type {
  fn from(native_type: NativeType) -> Self {
    match native_type {
      NativeType::Void => libffi::middle::Type::void(),
      NativeType::U8 => libffi::middle::Type::u8(),
      NativeType::I8 => libffi::middle::Type::i8(),
      NativeType::U16 => libffi::middle::Type::u16(),
      NativeType::I16 => libffi::middle::Type::i16(),
      NativeType::U32 => libffi::middle::Type::u32(),
      NativeType::I32 => libffi::middle::Type::i32(),
      NativeType::U64 => libffi::middle::Type::u64(),
      NativeType::I64 => libffi::middle::Type::i64(),
      NativeType::USize => libffi::middle::Type::usize(),
      NativeType::ISize => libffi::middle::Type::isize(),
      NativeType::F32 => libffi::middle::Type::f32(),
      NativeType::F64 => libffi::middle::Type::f64(),
      NativeType::Pointer => libffi::middle::Type::pointer(),
      NativeType::Function => libffi::middle::Type::pointer(),
    }
  }
}

/// Intermediate format for easy translation from NativeType + V8 value
/// to libffi argument types.
#[repr(C)]
union NativeValue {
  void_value: (),
  u8_value: u8,
  i8_value: i8,
  u16_value: u16,
  i16_value: i16,
  u32_value: u32,
  i32_value: i32,
  u64_value: u64,
  i64_value: i64,
  usize_value: usize,
  isize_value: isize,
  f32_value: f32,
  f64_value: f64,
  pointer: *const u8,
}

impl NativeValue {
  unsafe fn as_arg(&self, native_type: NativeType) -> Arg {
    match native_type {
      NativeType::Void => unreachable!(),
      NativeType::U8 => Arg::new(&self.u8_value),
      NativeType::I8 => Arg::new(&self.i8_value),
      NativeType::U16 => Arg::new(&self.u16_value),
      NativeType::I16 => Arg::new(&self.i16_value),
      NativeType::U32 => Arg::new(&self.u32_value),
      NativeType::I32 => Arg::new(&self.i32_value),
      NativeType::U64 => Arg::new(&self.u64_value),
      NativeType::I64 => Arg::new(&self.i64_value),
      NativeType::USize => Arg::new(&self.usize_value),
      NativeType::ISize => Arg::new(&self.isize_value),
      NativeType::F32 => Arg::new(&self.f32_value),
      NativeType::F64 => Arg::new(&self.f64_value),
      NativeType::Pointer | NativeType::Function => Arg::new(&self.pointer),
    }
  }

  // SAFETY: native_type must correspond to the type of value represented by the union field
  unsafe fn to_value(&self, native_type: NativeType) -> Value {
    match native_type {
      NativeType::Void => Value::Null,
      NativeType::U8 => Value::from(self.u8_value),
      NativeType::I8 => Value::from(self.i8_value),
      NativeType::U16 => Value::from(self.u16_value),
      NativeType::I16 => Value::from(self.i16_value),
      NativeType::U32 => Value::from(self.u32_value),
      NativeType::I32 => Value::from(self.i32_value),
      NativeType::U64 => {
        json!(U32x2::from(self.u64_value))
      }
      NativeType::I64 => {
        json!(U32x2::from(self.i64_value as u64))
      }
      NativeType::USize => {
        json!(U32x2::from(self.usize_value as u64))
      }
      NativeType::ISize => {
        json!(U32x2::from(self.isize_value as u64))
      }
      NativeType::F32 => Value::from(self.f32_value),
      NativeType::F64 => Value::from(self.f64_value),
      NativeType::Pointer | NativeType::Function => {
        json!(U32x2::from(self.pointer as u64))
      }
    }
  }

  // SAFETY: native_type must correspond to the type of value represented by the union field
  #[inline]
  unsafe fn to_v8<'scope>(
    &self,
    scope: &mut v8::HandleScope<'scope>,
    native_type: NativeType,
  ) -> serde_v8::Value<'scope> {
    match native_type {
      NativeType::Void => {
        let local_value: v8::Local<v8::Value> = v8::undefined(scope).into();
        local_value.into()
      }
      NativeType::U8 => {
        let local_value: v8::Local<v8::Value> =
          v8::Integer::new_from_unsigned(scope, self.u8_value as u32).into();
        local_value.into()
      }
      NativeType::I8 => {
        let local_value: v8::Local<v8::Value> =
          v8::Integer::new(scope, self.i8_value as i32).into();
        local_value.into()
      }
      NativeType::U16 => {
        let local_value: v8::Local<v8::Value> =
          v8::Integer::new_from_unsigned(scope, self.u16_value as u32).into();
        local_value.into()
      }
      NativeType::I16 => {
        let local_value: v8::Local<v8::Value> =
          v8::Integer::new(scope, self.i16_value as i32).into();
        local_value.into()
      }
      NativeType::U32 => {
        let local_value: v8::Local<v8::Value> =
          v8::Integer::new_from_unsigned(scope, self.u32_value).into();
        local_value.into()
      }
      NativeType::I32 => {
        let local_value: v8::Local<v8::Value> =
          v8::Integer::new(scope, self.i32_value).into();
        local_value.into()
      }
      NativeType::U64 => {
        let local_value: v8::Local<v8::Value> =
          v8::BigInt::new_from_u64(scope, self.u64_value).into();
        local_value.into()
      }
      NativeType::I64 => {
        let local_value: v8::Local<v8::Value> =
          v8::BigInt::new_from_i64(scope, self.i64_value).into();
        local_value.into()
      }
      NativeType::USize => {
        let local_value: v8::Local<v8::Value> =
          v8::BigInt::new_from_u64(scope, self.usize_value as u64).into();
        local_value.into()
      }
      NativeType::ISize => {
        let local_value: v8::Local<v8::Value> =
          v8::BigInt::new_from_i64(scope, self.isize_value as i64).into();
        local_value.into()
      }
      NativeType::F32 => {
        let local_value: v8::Local<v8::Value> =
          v8::Number::new(scope, self.f32_value as f64).into();
        local_value.into()
      }
      NativeType::F64 => {
        let local_value: v8::Local<v8::Value> =
          v8::Number::new(scope, self.f64_value).into();
        local_value.into()
      }
      NativeType::Pointer | NativeType::Function => {
        let local_value: v8::Local<v8::Value> =
          v8::BigInt::new_from_u64(scope, self.pointer as u64).into();
        local_value.into()
      }
    }
  }
}

unsafe impl Send for NativeValue {}

#[derive(Serialize, Debug, Clone, Copy)]
struct U32x2(u32, u32);

impl From<u64> for U32x2 {
  fn from(value: u64) -> Self {
    Self((value >> 32) as u32, value as u32)
  }
}

#[derive(Deserialize, Debug)]
#[serde(rename_all = "camelCase")]
struct ForeignFunction {
  name: Option<String>,
  parameters: Vec<NativeType>,
  result: NativeType,
  #[serde(rename = "nonblocking")]
  non_blocking: Option<bool>,
  #[serde(rename = "callback")]
  #[serde(default = "default_callback")]
  callback: bool,
}

fn default_callback() -> bool {
  false
}

// ForeignStatic's name and type fields are read and used by
// serde_v8 to determine which variant a ForeignSymbol is.
// They are not used beyond that and are thus marked with underscores.
#[derive(Deserialize, Debug)]
struct ForeignStatic {
  #[serde(rename(deserialize = "name"))]
  _name: Option<String>,
  #[serde(rename(deserialize = "type"))]
  _type: String,
}

#[derive(Deserialize, Debug)]
#[serde(untagged)]
enum ForeignSymbol {
  ForeignFunction(ForeignFunction),
  ForeignStatic(ForeignStatic),
}

#[derive(Deserialize, Debug)]
struct FfiLoadArgs {
  path: String,
  symbols: HashMap<String, ForeignSymbol>,
}

// `path` is only used on Windows.
#[allow(unused_variables)]
pub(crate) fn format_error(e: dlopen::Error, path: String) -> String {
  match e {
    #[cfg(target_os = "windows")]
    // This calls FormatMessageW with library path
    // as replacement for the insert sequences.
    // Unlike libstd which passes the FORMAT_MESSAGE_IGNORE_INSERTS
    // flag without any arguments.
    //
    // https://github.com/denoland/deno/issues/11632
    dlopen::Error::OpeningLibraryError(e) => {
      use std::ffi::OsStr;
      use std::os::windows::ffi::OsStrExt;
      use winapi::shared::minwindef::DWORD;
      use winapi::shared::winerror::ERROR_INSUFFICIENT_BUFFER;
      use winapi::um::errhandlingapi::GetLastError;
      use winapi::um::winbase::FormatMessageW;
      use winapi::um::winbase::FORMAT_MESSAGE_ARGUMENT_ARRAY;
      use winapi::um::winbase::FORMAT_MESSAGE_FROM_SYSTEM;
      use winapi::um::winnt::LANG_SYSTEM_DEFAULT;
      use winapi::um::winnt::MAKELANGID;
      use winapi::um::winnt::SUBLANG_SYS_DEFAULT;

      let err_num = match e.raw_os_error() {
        Some(err_num) => err_num,
        // This should never hit unless dlopen changes its error type.
        None => return e.to_string(),
      };

      // Language ID (0x0800)
      let lang_id =
        MAKELANGID(LANG_SYSTEM_DEFAULT, SUBLANG_SYS_DEFAULT) as DWORD;

      let mut buf = vec![0; 500];

      let path = OsStr::new(&path)
        .encode_wide()
        .chain(Some(0).into_iter())
        .collect::<Vec<_>>();

      let arguments = [path.as_ptr()];

      loop {
        unsafe {
          let length = FormatMessageW(
            FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ARGUMENT_ARRAY,
            std::ptr::null_mut(),
            err_num as DWORD,
            lang_id as DWORD,
            buf.as_mut_ptr(),
            buf.len() as DWORD,
            arguments.as_ptr() as _,
          );

          if length == 0 {
            let err_num = GetLastError();
            if err_num == ERROR_INSUFFICIENT_BUFFER {
              buf.resize(buf.len() * 2, 0);
              continue;
            }

            // Something went wrong, just return the original error.
            return e.to_string();
          }

          let msg = String::from_utf16_lossy(&buf[..length as usize]);
          return msg;
        }
      }
    }
    _ => e.to_string(),
  }
}

#[op(v8)]
fn op_ffi_load<FP, 'scope>(
  scope: &mut v8::HandleScope<'scope>,
  state: &mut deno_core::OpState,
  args: FfiLoadArgs,
) -> Result<(ResourceId, serde_v8::Value<'scope>), AnyError>
where
  FP: FfiPermissions + 'static,
{
  let path = args.path;

  check_unstable(state, "Deno.dlopen");
  let permissions = state.borrow_mut::<FP>();
  permissions.check(Some(&PathBuf::from(&path)))?;

  let lib = Library::open(&path).map_err(|e| {
    dlopen::Error::OpeningLibraryError(std::io::Error::new(
      std::io::ErrorKind::Other,
      format_error(e, path),
    ))
  })?;
  let mut resource = DynamicLibraryResource {
    lib,
    symbols: HashMap::new(),
  };
  let obj = v8::Object::new(scope);

  for (symbol_key, foreign_symbol) in args.symbols {
    match foreign_symbol {
      ForeignSymbol::ForeignStatic(_) => {
        // No-op: Statics will be handled separately and are not part of the Rust-side resource.
      }
      ForeignSymbol::ForeignFunction(foreign_fn) => {
        let symbol = match &foreign_fn.name {
          Some(symbol) => symbol,
          None => &symbol_key,
        };
        // By default, Err returned by this function does not tell
        // which symbol wasn't exported. So we'll modify the error
        // message to include the name of symbol.
        let fn_ptr =
          // SAFETY: The obtained T symbol is the size of a pointer.
          match unsafe { resource.lib.symbol::<*const c_void>(symbol) } {
            Ok(value) => Ok(value),
            Err(err) => Err(generic_error(format!(
              "Failed to register symbol {}: {}",
              symbol, err
            ))),
          }?;
        let ptr = libffi::middle::CodePtr::from_ptr(fn_ptr as _);
        let cif = libffi::middle::Cif::new(
          foreign_fn
            .parameters
            .clone()
            .into_iter()
            .map(libffi::middle::Type::from),
          foreign_fn.result.into(),
        );

        let func_key = v8::String::new(scope, &symbol_key).unwrap();
        let sym = Box::new(Symbol {
          cif,
          ptr,
          parameter_types: foreign_fn.parameters,
          result_type: foreign_fn.result,
          can_callback: foreign_fn.callback,
        });

        resource.symbols.insert(symbol_key, sym.clone());
        match foreign_fn.non_blocking {
          // Generate functions for synchronous calls.
          Some(false) | None => {
            let function = make_sync_fn(scope, sym);
            obj.set(scope, func_key.into(), function.into());
          }
          // This optimization is not yet supported for non-blocking calls.
          _ => {}
        };
      }
    }
  }

  let rid = state.resource_table.add(resource);
  Ok((
    rid,
    serde_v8::Value {
      v8_value: obj.into(),
    },
  ))
}

pub struct FfiFastCallTemplate {
  args: Box<[fast_api::Type]>,
  ret: fast_api::CType,
  symbol_ptr: *const c_void,
}

impl fast_api::FastFunction for FfiFastCallTemplate {
  type Signature = ();
  fn function(&self) -> Self::Signature {}

  fn raw(&self) -> *const c_void {
    self.symbol_ptr
  }
  fn args(&self) -> &'static [fast_api::Type] {
    Box::leak(self.args.clone())
  }
  fn return_type(&self) -> fast_api::CType {
    self.ret
  }
}

impl From<&NativeType> for fast_api::Type {
  fn from(native_type: &NativeType) -> Self {
    match native_type {
      NativeType::U8 | NativeType::U16 | NativeType::U32 => {
        fast_api::Type::Uint32
      }
      NativeType::I8 | NativeType::I16 | NativeType::I32 => {
        fast_api::Type::Int32
      }
      NativeType::F32 => fast_api::Type::Float32,
      NativeType::F64 => fast_api::Type::Float64,
      NativeType::Void => fast_api::Type::Void,
      NativeType::I64
      | NativeType::ISize
      | NativeType::U64
      | NativeType::USize => fast_api::Type::Uint64,
      NativeType::Function | NativeType::Pointer => {
        panic!("Cannot be fast api")
      }
    }
  }
}

#[cfg(not(target_os = "windows"))]
fn is_fast_api_rv(rv: NativeType) -> bool {
  !matches!(
    rv,
    NativeType::Function
      | NativeType::Pointer
      | NativeType::I64
      | NativeType::ISize
      | NativeType::U64
      | NativeType::USize
  )
}

#[cfg(not(target_os = "windows"))]
fn is_fast_api_arg(rv: NativeType) -> bool {
  !matches!(rv, NativeType::Function | NativeType::Pointer)
}

// Create a JavaScript function for synchronous FFI call to
// the given symbol.
fn make_sync_fn<'s>(
  scope: &mut v8::HandleScope<'s>,
  sym: Box<Symbol>,
) -> v8::Local<'s, v8::Function> {
  #[cfg(not(target_os = "windows"))]
  let mut fast_ffi_templ: Option<FfiFastCallTemplate> = None;

  #[cfg(target_os = "windows")]
  let fast_ffi_templ: Option<FfiFastCallTemplate> = None;

  #[cfg(not(target_os = "windows"))]
  let mut fast_allocations: Option<*mut ()> = None;
  #[cfg(not(target_os = "windows"))]
  if !sym.can_callback
    && !sym.parameter_types.iter().any(|t| !is_fast_api_arg(*t))
    && is_fast_api_rv(sym.result_type)
  {
    let ret = fast_api::Type::from(&sym.result_type);

    let mut args = sym
      .parameter_types
      .iter()
      .map(|t| t.into())
      .collect::<Vec<_>>();
    // recv
    args.insert(0, fast_api::Type::V8Value);
    let symbol_trampoline =
      jit_trampoline::gen_trampoline(sym.clone()).expect("gen_trampoline");
    fast_ffi_templ = Some(FfiFastCallTemplate {
      args: args.into_boxed_slice(),
      ret: (&ret).into(),
      symbol_ptr: symbol_trampoline.addr,
    });
    fast_allocations = Some(Box::into_raw(symbol_trampoline) as *mut ());
  }

  let sym = Box::leak(sym);
  let builder = v8::FunctionTemplate::builder(
    |scope: &mut v8::HandleScope,
     args: v8::FunctionCallbackArguments,
     mut rv: v8::ReturnValue| {
      let external: v8::Local<v8::External> =
        args.data().unwrap().try_into().unwrap();
      // SAFETY: The pointer will not be deallocated until the function is
      // garbage collected.
      let symbol = unsafe { &*(external.value() as *const Symbol) };
      match ffi_call_sync(scope, args, symbol) {
        Ok(result) => {
          // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
          let result = unsafe { result.to_v8(scope, symbol.result_type) };
          rv.set(result.v8_value);
        }
        Err(err) => {
          deno_core::_ops::throw_type_error(scope, err.to_string());
        }
      };
    },
  )
  .data(v8::External::new(scope, sym as *mut Symbol as *mut _).into());

  let func = if let Some(fast_ffi_templ) = fast_ffi_templ {
    builder.build_fast(scope, fast_ffi_templ)
  } else {
    builder.build(scope)
  };
  let func = func.get_function(scope).unwrap();

  let weak = v8::Weak::with_finalizer(
    scope,
    func,
    Box::new(move |_| {
      // SAFETY: This is never called twice. pointer obtained
      // from Box::into_raw, hence, satisfies memory layout requirements.
      unsafe {
        Box::from_raw(sym);
        #[cfg(not(target_os = "windows"))]
        if let Some(fast_allocations) = fast_allocations {
          Box::from_raw(fast_allocations as *mut jit_trampoline::Allocation);
        }
      }
    }),
  );

  weak.to_local(scope).unwrap()
}

fn ffi_parse_args<'scope>(
  scope: &mut v8::HandleScope<'scope>,
  args: serde_v8::Value<'scope>,
  parameter_types: &[NativeType],
) -> Result<Vec<NativeValue>, AnyError>
where
  'scope: 'scope,
{
  if parameter_types.is_empty() {
    return Ok(vec![]);
  }

  let args = v8::Local::<v8::Array>::try_from(args.v8_value)
    .map_err(|_| type_error("Invalid FFI parameters, expected Array"))?;
  let mut ffi_args: Vec<NativeValue> =
    Vec::with_capacity(parameter_types.len());

  for (index, native_type) in parameter_types.iter().enumerate() {
    let value = args.get_index(scope, index as u32).unwrap();
    match native_type {
      NativeType::Void => {
        unreachable!();
      }
      NativeType::U8 => {
        let value = value
          .uint32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI u8 type, expected number"))?
          as u8;
        ffi_args.push(NativeValue { u8_value: value });
      }
      NativeType::I8 => {
        let value = value
          .int32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI i8 type, expected number"))?
          as i8;
        ffi_args.push(NativeValue { i8_value: value });
      }
      NativeType::U16 => {
        let value = value
          .uint32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI u16 type, expected number"))?
          as u16;
        ffi_args.push(NativeValue { u16_value: value });
      }
      NativeType::I16 => {
        let value = value
          .int32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI i16 type, expected number"))?
          as i16;
        ffi_args.push(NativeValue { i16_value: value });
      }
      NativeType::U32 => {
        let value = value
          .uint32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI u32 type, expected number"))?
          as u32;
        ffi_args.push(NativeValue { u32_value: value });
      }
      NativeType::I32 => {
        let value = value
          .int32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI i32 type, expected number"))?
          as i32;
        ffi_args.push(NativeValue { i32_value: value });
      }
      NativeType::U64 => {
        let value: u64 =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.u64_value().0
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI u64 type, expected number")
            })? as u64
          };
        ffi_args.push(NativeValue { u64_value: value });
      }
      NativeType::I64 => {
        let value: i64 =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.i64_value().0
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI i64 type, expected number")
            })? as i64
          };
        ffi_args.push(NativeValue { i64_value: value });
      }
      NativeType::USize => {
        let value: usize =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.u64_value().0 as usize
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI usize type, expected number")
            })? as usize
          };
        ffi_args.push(NativeValue { usize_value: value });
      }
      NativeType::ISize => {
        let value: isize =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.i64_value().0 as isize
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI isize type, expected number")
            })? as isize
          };
        ffi_args.push(NativeValue { isize_value: value });
      }
      NativeType::F32 => {
        let value = value
          .number_value(scope)
          .ok_or_else(|| type_error("Invalid FFI f32 type, expected number"))?
          as f32;
        ffi_args.push(NativeValue { f32_value: value });
      }
      NativeType::F64 => {
        let value = value
          .number_value(scope)
          .ok_or_else(|| type_error("Invalid FFI f64 type, expected number"))?
          as f64;
        ffi_args.push(NativeValue { f64_value: value });
      }
      NativeType::Pointer => {
        if value.is_null() {
          let value: *const u8 = ptr::null();
          ffi_args.push(NativeValue { pointer: value })
        } else if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
          let value = value.u64_value().0 as *const u8;
          ffi_args.push(NativeValue { pointer: value });
        } else if let Ok(value) =
          v8::Local::<v8::ArrayBufferView>::try_from(value)
        {
          let byte_offset = value.byte_offset();
          let backing_store = value
            .buffer(scope)
            .ok_or_else(|| {
              type_error(
                "Invalid FFI ArrayBufferView, expected data in the buffer",
              )
            })?
            .get_backing_store();
          let pointer = if byte_offset > 0 {
            &backing_store[byte_offset..] as *const _ as *const u8
          } else {
            &backing_store[..] as *const _ as *const u8
          };
          ffi_args.push(NativeValue { pointer });
        } else if let Ok(value) = v8::Local::<v8::ArrayBuffer>::try_from(value)
        {
          let backing_store = value.get_backing_store();
          let pointer = &backing_store[..] as *const _ as *const u8;
          ffi_args.push(NativeValue { pointer });
        } else {
          return Err(type_error("Invalid FFI pointer type, expected null, BigInt, ArrayBuffer, or ArrayBufferView"));
        }
      }
      NativeType::Function => {
        if value.is_null() {
          let value: *const u8 = ptr::null();
          ffi_args.push(NativeValue { pointer: value })
        } else if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
          let value = value.u64_value().0 as *const u8;
          ffi_args.push(NativeValue { pointer: value });
        } else {
          return Err(type_error(
            "Invalid FFI function type, expected null, or BigInt",
          ));
        }
      }
    }
  }

  Ok(ffi_args)
}

// A one-off synchronous FFI call.
fn ffi_call_sync<'scope>(
  scope: &mut v8::HandleScope<'scope>,
  args: v8::FunctionCallbackArguments,
  symbol: &Symbol,
) -> Result<NativeValue, AnyError>
where
  'scope: 'scope,
{
  let Symbol {
    parameter_types,
    result_type,
    cif,
    ptr: fun_ptr,
    ..
  } = symbol;
  let mut ffi_args: Vec<NativeValue> =
    Vec::with_capacity(parameter_types.len());

  for (index, native_type) in parameter_types.iter().enumerate() {
    let value = args.get(index as i32);
    match native_type {
      NativeType::Void => {
        unreachable!();
      }
      NativeType::U8 => {
        let value = value
          .uint32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI u8 type, expected number"))?
          as u8;
        ffi_args.push(NativeValue { u8_value: value });
      }
      NativeType::I8 => {
        let value = value
          .int32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI i8 type, expected number"))?
          as i8;

        ffi_args.push(NativeValue { i8_value: value });
      }
      NativeType::U16 => {
        let value = value
          .uint32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI u16 type, expected number"))?
          as u16;

        ffi_args.push(NativeValue { u16_value: value });
      }
      NativeType::I16 => {
        let value = value
          .int32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI i16 type, expected number"))?
          as i16;

        ffi_args.push(NativeValue { i16_value: value });
      }
      NativeType::U32 => {
        let value = value
          .uint32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI u32 type, expected number"))?
          as u32;

        ffi_args.push(NativeValue { u32_value: value });
      }
      NativeType::I32 => {
        let value = value
          .int32_value(scope)
          .ok_or_else(|| type_error("Invalid FFI i32 type, expected number"))?
          as i32;

        ffi_args.push(NativeValue { i32_value: value });
      }
      NativeType::U64 => {
        let value: u64 =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.u64_value().0
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI u64 type, expected number")
            })? as u64
          };

        ffi_args.push(NativeValue { u64_value: value });
      }
      NativeType::I64 => {
        let value: i64 =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.i64_value().0
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI i64 type, expected number")
            })? as i64
          };

        ffi_args.push(NativeValue { i64_value: value });
      }
      NativeType::USize => {
        let value: usize =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.u64_value().0 as usize
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI usize type, expected number")
            })? as usize
          };

        ffi_args.push(NativeValue { usize_value: value });
      }
      NativeType::ISize => {
        let value: isize =
          if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
            value.i64_value().0 as isize
          } else {
            value.integer_value(scope).ok_or_else(|| {
              type_error("Invalid FFI isize type, expected number")
            })? as isize
          };

        ffi_args.push(NativeValue { isize_value: value });
      }
      NativeType::F32 => {
        let value = value
          .number_value(scope)
          .ok_or_else(|| type_error("Invalid FFI f32 type, expected number"))?
          as f32;

        ffi_args.push(NativeValue { f32_value: value });
      }
      NativeType::F64 => {
        let value = value
          .number_value(scope)
          .ok_or_else(|| type_error("Invalid FFI f64 type, expected number"))?
          as f64;
        ffi_args.push(NativeValue { f64_value: value });
      }
      NativeType::Pointer => {
        if value.is_null() {
          let value: *const u8 = ptr::null();

          ffi_args.push(NativeValue { pointer: value })
        } else if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
          let value = value.u64_value().0 as *const u8;

          ffi_args.push(NativeValue { pointer: value });
        } else if let Ok(value) =
          v8::Local::<v8::ArrayBufferView>::try_from(value)
        {
          let byte_offset = value.byte_offset();
          let backing_store = value
            .buffer(scope)
            .ok_or_else(|| {
              type_error(
                "Invalid FFI ArrayBufferView, expected data in the buffer",
              )
            })?
            .get_backing_store();
          let pointer = if byte_offset > 0 {
            &backing_store[byte_offset..] as *const _ as *const u8
          } else {
            &backing_store[..] as *const _ as *const u8
          };

          ffi_args.push(NativeValue { pointer });
        } else if let Ok(value) = v8::Local::<v8::ArrayBuffer>::try_from(value)
        {
          let backing_store = value.get_backing_store();
          let pointer = &backing_store[..] as *const _ as *const u8;

          ffi_args.push(NativeValue { pointer });
        } else {
          return Err(type_error("Invalid FFI pointer type, expected null, BigInt, ArrayBuffer, or ArrayBufferView"));
        }
      }
      NativeType::Function => {
        if value.is_null() {
          let value: *const u8 = ptr::null();
          ffi_args.push(NativeValue { pointer: value })
        } else if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
          let value = value.u64_value().0 as *const u8;
          ffi_args.push(NativeValue { pointer: value });
        } else {
          return Err(type_error(
            "Invalid FFI function type, expected null, or BigInt",
          ));
        }
      }
    }
  }
  let call_args: Vec<Arg> = ffi_args.iter().map(Arg::new).collect();
  // SAFETY: types in the `Cif` match the actual calling convention and
  // types of symbol.
  unsafe {
    Ok(match result_type {
      NativeType::Void => NativeValue {
        void_value: cif.call::<()>(*fun_ptr, &call_args),
      },
      NativeType::U8 => NativeValue {
        u8_value: cif.call::<u8>(*fun_ptr, &call_args),
      },
      NativeType::I8 => NativeValue {
        i8_value: cif.call::<i8>(*fun_ptr, &call_args),
      },
      NativeType::U16 => NativeValue {
        u16_value: cif.call::<u16>(*fun_ptr, &call_args),
      },
      NativeType::I16 => NativeValue {
        i16_value: cif.call::<i16>(*fun_ptr, &call_args),
      },
      NativeType::U32 => NativeValue {
        u32_value: cif.call::<u32>(*fun_ptr, &call_args),
      },
      NativeType::I32 => NativeValue {
        i32_value: cif.call::<i32>(*fun_ptr, &call_args),
      },
      NativeType::U64 => NativeValue {
        u64_value: cif.call::<u64>(*fun_ptr, &call_args),
      },
      NativeType::I64 => NativeValue {
        i64_value: cif.call::<i64>(*fun_ptr, &call_args),
      },
      NativeType::USize => NativeValue {
        usize_value: cif.call::<usize>(*fun_ptr, &call_args),
      },
      NativeType::ISize => NativeValue {
        isize_value: cif.call::<isize>(*fun_ptr, &call_args),
      },
      NativeType::F32 => NativeValue {
        f32_value: cif.call::<f32>(*fun_ptr, &call_args),
      },
      NativeType::F64 => NativeValue {
        f64_value: cif.call::<f64>(*fun_ptr, &call_args),
      },
      NativeType::Pointer | NativeType::Function => NativeValue {
        pointer: cif.call::<*const u8>(*fun_ptr, &call_args),
      },
    })
  }
}

fn ffi_call(
  call_args: Vec<NativeValue>,
  cif: &libffi::middle::Cif,
  fun_ptr: libffi::middle::CodePtr,
  parameter_types: &[NativeType],
  result_type: NativeType,
) -> Result<NativeValue, AnyError> {
  let call_args: Vec<Arg> = call_args
    .iter()
    .enumerate()
    .map(|(index, ffi_arg)| {
      // SAFETY: the union field is initialized
      unsafe { ffi_arg.as_arg(*parameter_types.get(index).unwrap()) }
    })
    .collect();

  // SAFETY: types in the `Cif` match the actual calling convention and
  // types of symbol.
  unsafe {
    Ok(match result_type {
      NativeType::Void => NativeValue {
        void_value: cif.call::<()>(fun_ptr, &call_args),
      },
      NativeType::U8 => NativeValue {
        u8_value: cif.call::<u8>(fun_ptr, &call_args),
      },
      NativeType::I8 => NativeValue {
        i8_value: cif.call::<i8>(fun_ptr, &call_args),
      },
      NativeType::U16 => NativeValue {
        u16_value: cif.call::<u16>(fun_ptr, &call_args),
      },
      NativeType::I16 => NativeValue {
        i16_value: cif.call::<i16>(fun_ptr, &call_args),
      },
      NativeType::U32 => NativeValue {
        u32_value: cif.call::<u32>(fun_ptr, &call_args),
      },
      NativeType::I32 => NativeValue {
        i32_value: cif.call::<i32>(fun_ptr, &call_args),
      },
      NativeType::U64 => NativeValue {
        u64_value: cif.call::<u64>(fun_ptr, &call_args),
      },
      NativeType::I64 => NativeValue {
        i64_value: cif.call::<i64>(fun_ptr, &call_args),
      },
      NativeType::USize => NativeValue {
        usize_value: cif.call::<usize>(fun_ptr, &call_args),
      },
      NativeType::ISize => NativeValue {
        isize_value: cif.call::<isize>(fun_ptr, &call_args),
      },
      NativeType::F32 => NativeValue {
        f32_value: cif.call::<f32>(fun_ptr, &call_args),
      },
      NativeType::F64 => NativeValue {
        f64_value: cif.call::<f64>(fun_ptr, &call_args),
      },
      NativeType::Pointer | NativeType::Function => NativeValue {
        pointer: cif.call::<*const u8>(fun_ptr, &call_args),
      },
    })
  }
}

struct UnsafeCallbackResource {
  // Closure is never directly touched, but it keeps the C callback alive
  // until `close()` method is called.
  #[allow(dead_code)]
  closure: libffi::middle::Closure<'static>,
  info: *const CallbackInfo,
}

impl Resource for UnsafeCallbackResource {
  fn name(&self) -> Cow<str> {
    "unsafecallback".into()
  }

  fn close(self: Rc<Self>) {
    // SAFETY: This drops the closure and the callback info associated with it.
    // Any retained function pointers to the closure become dangling pointers.
    // It is up to the user to know that it is safe to call the `close()` on the
    // UnsafeCallback instance.
    unsafe {
      let info = Box::from_raw(self.info as *mut CallbackInfo);
      let isolate = info.isolate.as_mut().unwrap();
      v8::Global::from_raw(isolate, info.callback);
      v8::Global::from_raw(isolate, info.context);
    }
  }
}

struct CallbackInfo {
  pub async_work_sender: mpsc::UnboundedSender<PendingFfiAsyncWork>,
  pub callback: NonNull<v8::Function>,
  pub context: NonNull<v8::Context>,
  pub isolate: *mut v8::Isolate,
}

unsafe extern "C" fn deno_ffi_callback(
  cif: &libffi::low::ffi_cif,
  result: &mut c_void,
  args: *const *const c_void,
  info: &CallbackInfo,
) {
  LOCAL_ISOLATE_POINTER.with(|s| {
    if ptr::eq(*s.borrow(), info.isolate) {
      // Own isolate thread, okay to call directly
      do_ffi_callback(
        cif,
        result,
        args,
        info.callback,
        info.context,
        info.isolate,
      );
    } else {
      let async_work_sender = &info.async_work_sender;
      // SAFETY: Safe as this function blocks until `do_ffi_callback` completes and a response message is received.
      let cif: &'static libffi::low::ffi_cif = std::mem::transmute(cif);
      let result: &'static mut c_void = std::mem::transmute(result);
      let info: &'static CallbackInfo = std::mem::transmute(info);
      let (response_sender, response_receiver) = sync_channel::<()>(0);
      let fut = Box::new(move || {
        do_ffi_callback(
          cif,
          result,
          args,
          info.callback,
          info.context,
          info.isolate,
        );
        response_sender.send(()).unwrap();
      });
      async_work_sender.unbounded_send(fut).unwrap();
      response_receiver.recv().unwrap();
    }
  });
}

unsafe fn do_ffi_callback(
  cif: &libffi::low::ffi_cif,
  result: &mut c_void,
  args: *const *const c_void,
  callback: NonNull<v8::Function>,
  context: NonNull<v8::Context>,
  isolate: *mut v8::Isolate,
) {
  let isolate = &mut *isolate;
  let callback = v8::Global::from_raw(isolate, callback);
  let context = std::mem::transmute::<
    NonNull<v8::Context>,
    v8::Local<v8::Context>,
  >(context);
  // Call from main thread. If this callback is being triggered due to a
  // function call coming from Deno itself, then this callback will build
  // ontop of that stack.
  // If this callback is being triggered outside of Deno (for example from a
  // signal handler) then this will either create an empty new stack if
  // Deno currently has nothing running and is waiting for promises to resolve,
  // or will (very incorrectly) build ontop of whatever stack exists.
  // The callback will even be called through from a `while (true)` liveloop, but
  // it somehow cannot change the values that the loop sees, even if they both
  // refer the same `let bool_value`.
  let mut cb_scope = v8::CallbackScope::new(context);
  let mut scope = v8::HandleScope::new(&mut cb_scope);
  let func = callback.open(&mut scope);
  let result = result as *mut c_void;
  let repr: &[*mut ffi_type] =
    std::slice::from_raw_parts(cif.arg_types, cif.nargs as usize);
  let vals: &[*const c_void] =
    std::slice::from_raw_parts(args, cif.nargs as usize);

  let mut params: Vec<v8::Local<v8::Value>> = vec![];
  for (repr, val) in repr.iter().zip(vals) {
    let value: v8::Local<v8::Value> = match (*(*repr)).type_ as _ {
      FFI_TYPE_FLOAT => {
        let value = *((*val) as *const f32);
        v8::Number::new(&mut scope, value as f64).into()
      }
      FFI_TYPE_DOUBLE => {
        let value = *((*val) as *const f64);
        v8::Number::new(&mut scope, value).into()
      }
      FFI_TYPE_SINT8 => {
        let value = *((*val) as *const i8);
        v8::Integer::new(&mut scope, value as i32).into()
      }
      FFI_TYPE_UINT8 => {
        let value = *((*val) as *const u8);
        v8::Integer::new_from_unsigned(&mut scope, value as u32).into()
      }
      FFI_TYPE_SINT16 => {
        let value = *((*val) as *const i16);
        v8::Integer::new(&mut scope, value as i32).into()
      }
      FFI_TYPE_UINT16 => {
        let value = *((*val) as *const u16);
        v8::Integer::new_from_unsigned(&mut scope, value as u32).into()
      }
      FFI_TYPE_INT | FFI_TYPE_SINT32 => {
        let value = *((*val) as *const i32);
        v8::Integer::new(&mut scope, value).into()
      }
      FFI_TYPE_UINT32 => {
        let value = *((*val) as *const u32);
        v8::Integer::new_from_unsigned(&mut scope, value).into()
      }
      FFI_TYPE_SINT64 => {
        let result = *((*val) as *const i64);
        v8::BigInt::new_from_i64(&mut scope, result).into()
      }
      FFI_TYPE_POINTER | FFI_TYPE_STRUCT | FFI_TYPE_UINT64 => {
        let result = *((*val) as *const u64);
        v8::BigInt::new_from_u64(&mut scope, result).into()
      }
      FFI_TYPE_VOID => v8::undefined(&mut scope).into(),
      _ => {
        unreachable!()
      }
    };
    params.push(value);
  }

  let recv = v8::undefined(&mut scope);
  let call_result = func.call(&mut scope, recv.into(), &params);
  std::mem::forget(callback);

  if call_result.is_none() {
    // JS function threw an exception. Set the return value to zero and return.
    // The exception continue propagating up the call chain when the event loop
    // resumes.
    match (*cif.rtype).type_ as _ {
      FFI_TYPE_INT | FFI_TYPE_SINT32 | FFI_TYPE_UINT32 => {
        // zero is equal for signed and unsigned alike
        *(result as *mut u32) = 0;
      }
      FFI_TYPE_FLOAT => {
        *(result as *mut f32) = 0.0;
      }
      FFI_TYPE_DOUBLE => {
        *(result as *mut f64) = 0.0;
      }
      FFI_TYPE_SINT8 | FFI_TYPE_UINT8 => {
        // zero is equal for signed and unsigned alike
        *(result as *mut u8) = 0;
      }
      FFI_TYPE_SINT16 | FFI_TYPE_UINT16 => {
        // zero is equal for signed and unsigned alike
        *(result as *mut u16) = 0;
      }
      FFI_TYPE_POINTER | FFI_TYPE_STRUCT | FFI_TYPE_UINT64
      | FFI_TYPE_SINT64 => {
        *(result as *mut u64) = 0;
      }
      FFI_TYPE_VOID => {
        // nop
      }
      _ => {
        unreachable!();
      }
    };

    return;
  }
  let value = call_result.unwrap();

  match (*cif.rtype).type_ as _ {
    FFI_TYPE_INT | FFI_TYPE_SINT32 => {
      *(result as *mut i32) = value
        .int32_value(&mut scope)
        .expect("Unable to deserialize result parameter.")
        as i32;
    }
    FFI_TYPE_FLOAT => {
      *(result as *mut f32) = value
        .number_value(&mut scope)
        .expect("Unable to deserialize result parameter.")
        as f32;
    }
    FFI_TYPE_DOUBLE => {
      *(result as *mut f64) = value
        .number_value(&mut scope)
        .expect("Unable to deserialize result parameter.");
    }
    FFI_TYPE_POINTER | FFI_TYPE_STRUCT => {
      if let Ok(value) = v8::Local::<v8::ArrayBufferView>::try_from(value) {
        let byte_offset = value.byte_offset();
        let backing_store = value
          .buffer(&mut scope)
          .expect("Unable to deserialize result parameter.")
          .get_backing_store();
        let pointer = if byte_offset > 0 {
          &backing_store[byte_offset..] as *const _ as *const u8
        } else {
          &backing_store[..] as *const _ as *const u8
        };
        *(result as *mut *const u8) = pointer;
      } else if let Ok(value) = v8::Local::<v8::ArrayBuffer>::try_from(value) {
        let backing_store = value.get_backing_store();
        let pointer = &backing_store[..] as *const _ as *const u8;
        *(result as *mut *const u8) = pointer;
      } else if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
        *(result as *mut u64) = value.u64_value().0;
      } else if value.is_null() {
        *(result as *mut *const c_void) = ptr::null();
      } else {
        // Fallthrough: Probably someone returned a number but this could
        // also be eg. a string. This is essentially UB.
        *(result as *mut u64) = value
          .integer_value(&mut scope)
          .expect("Unable to deserialize result parameter.")
          as u64;
      }
    }
    FFI_TYPE_SINT8 => {
      *(result as *mut i8) = value
        .int32_value(&mut scope)
        .expect("Unable to deserialize result parameter.")
        as i8;
    }
    FFI_TYPE_UINT8 => {
      *(result as *mut u8) = value
        .uint32_value(&mut scope)
        .expect("Unable to deserialize result parameter.")
        as u8;
    }
    FFI_TYPE_SINT16 => {
      *(result as *mut i16) = value
        .int32_value(&mut scope)
        .expect("Unable to deserialize result parameter.")
        as i16;
    }
    FFI_TYPE_UINT16 => {
      *(result as *mut u16) = value
        .uint32_value(&mut scope)
        .expect("Unable to deserialize result parameter.")
        as u16;
    }
    FFI_TYPE_UINT32 => {
      *(result as *mut u32) = value
        .uint32_value(&mut scope)
        .expect("Unable to deserialize result parameter.");
    }
    FFI_TYPE_SINT64 => {
      if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
        *(result as *mut i64) = value.i64_value().0;
      } else {
        *(result as *mut i64) = value
          .integer_value(&mut scope)
          .expect("Unable to deserialize result parameter.")
          as i64;
      }
    }
    FFI_TYPE_UINT64 => {
      if let Ok(value) = v8::Local::<v8::BigInt>::try_from(value) {
        *(result as *mut u64) = value.u64_value().0;
      } else {
        *(result as *mut u64) = value
          .integer_value(&mut scope)
          .expect("Unable to deserialize result parameter.")
          as u64;
      }
    }
    FFI_TYPE_VOID => {
      // nop
    }
    _ => {
      unreachable!();
    }
  };
}

#[derive(Deserialize)]
struct RegisterCallbackArgs {
  parameters: Vec<NativeType>,
  result: NativeType,
}

#[op(v8)]
fn op_ffi_unsafe_callback_create<FP, 'scope>(
  state: &mut deno_core::OpState,
  scope: &mut v8::HandleScope<'scope>,
  args: RegisterCallbackArgs,
  cb: serde_v8::Value<'scope>,
) -> Result<serde_v8::Value<'scope>, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafeCallback");
  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  let v8_value = cb.v8_value;
  let cb = v8::Local::<v8::Function>::try_from(v8_value)?;

  let isolate: *mut v8::Isolate = &mut *scope as &mut v8::Isolate;
  LOCAL_ISOLATE_POINTER.with(|s| {
    if s.borrow().is_null() {
      s.replace(isolate);
    }
  });

  let async_work_sender =
    state.borrow_mut::<FfiState>().async_work_sender.clone();
  let callback = v8::Global::new(scope, cb).into_raw();
  let current_context = scope.get_current_context();
  let context = v8::Global::new(scope, current_context).into_raw();

  let info = Box::leak(Box::new(CallbackInfo {
    async_work_sender,
    callback,
    context,
    isolate,
  }));
  let cif = Cif::new(
    args.parameters.into_iter().map(libffi::middle::Type::from),
    libffi::middle::Type::from(args.result),
  );

  let closure = libffi::middle::Closure::new(cif, deno_ffi_callback, info);
  let ptr = *closure.code_ptr() as usize as u64;
  let resource = UnsafeCallbackResource { closure, info };
  let rid = state.resource_table.add(resource);

  let rid_local = v8::Integer::new_from_unsigned(scope, rid);
  let ptr_local = v8::BigInt::new_from_u64(scope, ptr);
  let array = v8::Array::new(scope, 2);
  array.set_index(scope, 0, rid_local.into());
  array.set_index(scope, 1, ptr_local.into());
  let array_value: v8::Local<v8::Value> = array.into();

  Ok(array_value.into())
}

#[op(v8)]
fn op_ffi_call_ptr<FP, 'scope>(
  scope: &mut v8::HandleScope<'scope>,
  state: Rc<RefCell<deno_core::OpState>>,
  pointer: u64,
  def: ForeignFunction,
  parameters: serde_v8::Value<'scope>,
) -> Result<serde_v8::Value<'scope>, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable2(&state, "Deno.UnsafeFnPointer#call");
  {
    let mut state = state.borrow_mut();
    let permissions = state.borrow_mut::<FP>();
    permissions.check(None)?;
  };

  let symbol = PtrSymbol::new(pointer, &def);
  let call_args = ffi_parse_args(scope, parameters, &def.parameters)?;

  let result = ffi_call(
    call_args,
    &symbol.cif,
    symbol.ptr,
    &def.parameters,
    def.result,
  )?;
  // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
  let result = unsafe { result.to_v8(scope, def.result) };
  Ok(result)
}

#[op]
fn op_ffi_unsafe_callback_ref(state: &mut deno_core::OpState, inc_dec: bool) {
  let ffi_state = state.borrow_mut::<FfiState>();
  if inc_dec {
    ffi_state.active_refed_functions += 1;
  } else {
    ffi_state.active_refed_functions -= 1;
  }
}

#[op(v8)]
fn op_ffi_call_ptr_nonblocking<'scope, FP>(
  scope: &mut v8::HandleScope<'scope>,
  state: Rc<RefCell<deno_core::OpState>>,
  pointer: u64,
  def: ForeignFunction,
  parameters: serde_v8::Value<'scope>,
) -> Result<impl Future<Output = Result<Value, AnyError>>, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable2(&state, "Deno.UnsafeFnPointer#call");
  {
    let mut state = state.borrow_mut();
    let permissions = state.borrow_mut::<FP>();
    permissions.check(None)?;
  };

  let symbol = PtrSymbol::new(pointer, &def);
  let call_args = ffi_parse_args(scope, parameters, &def.parameters)?;

  let join_handle = tokio::task::spawn_blocking(move || {
    let PtrSymbol { cif, ptr } = symbol.clone();
    ffi_call(call_args, &cif, ptr, &def.parameters, def.result)
  });

  Ok(async move {
    let result = join_handle
      .await
      .map_err(|err| anyhow!("Nonblocking FFI call failed: {}", err))??;
    // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
    Ok(unsafe { result.to_value(def.result) })
  })
}

#[op(v8)]
fn op_ffi_get_static<'scope>(
  scope: &mut v8::HandleScope<'scope>,
  state: &mut deno_core::OpState,
  rid: ResourceId,
  name: String,
  static_type: NativeType,
) -> Result<serde_v8::Value<'scope>, AnyError> {
  let resource = state.resource_table.get::<DynamicLibraryResource>(rid)?;

  let data_ptr = resource.get_static(name)?;

  Ok(match static_type {
    NativeType::Void => {
      return Err(type_error("Invalid FFI static type 'void'"));
    }
    NativeType::U8 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const u8) };
      let number: v8::Local<v8::Value> =
        v8::Integer::new_from_unsigned(scope, result as u32).into();
      number.into()
    }
    NativeType::I8 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const i8) };
      let number: v8::Local<v8::Value> =
        v8::Integer::new(scope, result as i32).into();
      number.into()
    }
    NativeType::U16 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const u16) };
      let number: v8::Local<v8::Value> =
        v8::Integer::new_from_unsigned(scope, result as u32).into();
      number.into()
    }
    NativeType::I16 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const i16) };
      let number: v8::Local<v8::Value> =
        v8::Integer::new(scope, result as i32).into();
      number.into()
    }
    NativeType::U32 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const u32) };
      let number: v8::Local<v8::Value> =
        v8::Integer::new_from_unsigned(scope, result).into();
      number.into()
    }
    NativeType::I32 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const i32) };
      let number: v8::Local<v8::Value> = v8::Integer::new(scope, result).into();
      number.into()
    }
    NativeType::U64 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const u64) };
      let big_int: v8::Local<v8::Value> =
        v8::BigInt::new_from_u64(scope, result).into();
      big_int.into()
    }
    NativeType::I64 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const i64) };
      let big_int: v8::Local<v8::Value> =
        v8::BigInt::new_from_i64(scope, result).into();
      big_int.into()
    }
    NativeType::USize => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const usize) };
      let big_int: v8::Local<v8::Value> =
        v8::BigInt::new_from_u64(scope, result as u64).into();
      big_int.into()
    }
    NativeType::ISize => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const isize) };
      let big_int: v8::Local<v8::Value> =
        v8::BigInt::new_from_i64(scope, result as i64).into();
      big_int.into()
    }
    NativeType::F32 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const f32) };
      let number: v8::Local<v8::Value> =
        v8::Number::new(scope, result as f64).into();
      number.into()
    }
    NativeType::F64 => {
      // SAFETY: ptr is user provided
      let result = unsafe { ptr::read_unaligned(data_ptr as *const f64) };
      let number: v8::Local<v8::Value> = v8::Number::new(scope, result).into();
      number.into()
    }
    NativeType::Pointer | NativeType::Function => {
      let result = data_ptr as u64;
      let big_int: v8::Local<v8::Value> =
        v8::BigInt::new_from_u64(scope, result).into();
      big_int.into()
    }
  })
}

/// A non-blocking FFI call.
#[op(v8)]
fn op_ffi_call_nonblocking<'scope>(
  scope: &mut v8::HandleScope<'scope>,
  state: Rc<RefCell<deno_core::OpState>>,
  rid: ResourceId,
  symbol: String,
  parameters: serde_v8::Value<'scope>,
) -> Result<impl Future<Output = Result<Value, AnyError>> + 'static, AnyError> {
  let symbol = {
    let state = state.borrow();
    let resource = state.resource_table.get::<DynamicLibraryResource>(rid)?;
    let symbols = &resource.symbols;
    *symbols
      .get(&symbol)
      .ok_or_else(|| type_error("Invalid FFI symbol name"))?
      .clone()
  };

  let call_args = ffi_parse_args(scope, parameters, &symbol.parameter_types)?;

  let result_type = symbol.result_type;
  let join_handle = tokio::task::spawn_blocking(move || {
    let Symbol {
      cif,
      ptr,
      parameter_types,
      result_type,
      ..
    } = symbol.clone();
    ffi_call(call_args, &cif, ptr, &parameter_types, result_type)
  });

  Ok(async move {
    let result = join_handle
      .await
      .map_err(|err| anyhow!("Nonblocking FFI call failed: {}", err))??;
    // SAFETY: Same return type declared to libffi; trust user to have it right beyond that.
    Ok(unsafe { result.to_value(result_type) })
  })
}

#[op(v8)]
fn op_ffi_ptr_of<FP, 'scope>(
  scope: &mut v8::HandleScope<'scope>,
  state: &mut deno_core::OpState,
  buf: ZeroCopyBuf,
) -> Result<serde_v8::Value<'scope>, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointer#of");
  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  let big_int: v8::Local<v8::Value> =
    v8::BigInt::new_from_u64(scope, buf.as_ptr() as u64).into();
  Ok(big_int.into())
}

#[op]
fn op_ffi_buf_copy_into<FP>(
  state: &mut deno_core::OpState,
  src: u64,
  mut dst: ZeroCopyBuf,
  len: usize,
) -> Result<(), AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#copyInto");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  if dst.len() < len {
    Err(range_error(
      "Destination length is smaller than source length",
    ))
  } else {
    let src = src as *const u8;
    // SAFETY: src is user defined.
    // dest is properly aligned and is valid for writes of len * size_of::<T>() bytes.
    unsafe { ptr::copy(src, dst.as_mut_ptr(), len) };
    Ok(())
  }
}

#[op]
fn op_ffi_cstr_read<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<String, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getCString");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  let ptr = ptr as *const c_char;
  // SAFETY: ptr is user provided
  // lifetime validity is not an issue because we allocate a new string.
  Ok(unsafe { CStr::from_ptr(ptr) }.to_str()?.to_string())
}

#[op]
fn op_ffi_read_u8<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<u8, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getUint8");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const u8) })
}

#[op]
fn op_ffi_read_i8<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<i8, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getInt8");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const i8) })
}

#[op]
fn op_ffi_read_u16<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<u16, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getUint16");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const u16) })
}

#[op]
fn op_ffi_read_i16<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<i16, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getInt16");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const i16) })
}

#[op]
fn op_ffi_read_u32<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<u32, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getUint32");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const u32) })
}

#[op]
fn op_ffi_read_i32<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<i32, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getInt32");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const i32) })
}

#[op(v8)]
fn op_ffi_read_u64<FP, 'scope>(
  scope: &mut v8::HandleScope<'scope>,
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<serde_v8::Value<'scope>, AnyError>
where
  FP: FfiPermissions + 'static,
  'scope: 'scope,
{
  check_unstable(state, "Deno.UnsafePointerView#getBigUint64");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  let result = unsafe { ptr::read_unaligned(ptr as *const u64) };

  let big_int: v8::Local<v8::Value> =
    v8::BigInt::new_from_u64(scope, result).into();
  Ok(big_int.into())
}

#[op]
fn op_ffi_read_f32<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<f32, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getFloat32");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const f32) })
}

#[op]
fn op_ffi_read_f64<FP>(
  state: &mut deno_core::OpState,
  ptr: u64,
) -> Result<f64, AnyError>
where
  FP: FfiPermissions + 'static,
{
  check_unstable(state, "Deno.UnsafePointerView#getFloat64");

  let permissions = state.borrow_mut::<FP>();
  permissions.check(None)?;

  // SAFETY: ptr is user provided.
  Ok(unsafe { ptr::read_unaligned(ptr as *const f64) })
}

#[cfg(test)]
mod tests {
  #[cfg(target_os = "windows")]
  #[test]
  fn test_format_error() {
    use super::format_error;

    // BAD_EXE_FORMAT
    let err = dlopen::Error::OpeningLibraryError(
      std::io::Error::from_raw_os_error(0x000000C1),
    );
    assert_eq!(
      format_error(err, "foo.dll".to_string()),
      "foo.dll is not a valid Win32 application.\r\n".to_string(),
    );
  }
}