denoland-deno/runtime/inspector.rs

// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.

//! The documentation for the inspector API is sparse, but these are helpful:
//! https://chromedevtools.github.io/devtools-protocol/
//! https://hyperandroid.com/2020/02/12/v8-inspector-from-an-embedder-standpoint/

use core::convert::Infallible as Never; // Alias for the future `!` type.
use deno_core::error::generic_error;
use deno_core::error::AnyError;
use deno_core::futures::channel::mpsc;
use deno_core::futures::channel::mpsc::UnboundedReceiver;
use deno_core::futures::channel::mpsc::UnboundedSender;
use deno_core::futures::channel::oneshot;
use deno_core::futures::future::{self, Future};
use deno_core::futures::pin_mut;
use deno_core::futures::prelude::*;
use deno_core::futures::select;
use deno_core::futures::stream::FuturesUnordered;
use deno_core::futures::stream::StreamExt;
use deno_core::futures::task;
use deno_core::futures::task::Context;
use deno_core::futures::task::Poll;
use deno_core::serde_json;
use deno_core::serde_json::json;
use deno_core::serde_json::Value;
use deno_core::v8;
use deno_websocket::tokio_tungstenite::tungstenite;
use std::collections::HashMap;
use std::ffi::c_void;
use std::mem::replace;
use std::mem::take;
use std::mem::MaybeUninit;
use std::net::SocketAddr;
use std::ops::Deref;
use std::ops::DerefMut;
use std::pin::Pin;
use std::process;
use std::ptr;
use std::ptr::NonNull;
use std::sync::Arc;
use std::sync::Mutex;
use std::thread;
use std::{cell::BorrowMutError, convert::Infallible};
use std::{cell::RefCell, rc::Rc};
use uuid::Uuid;

pub struct InspectorServer {
  pub host: SocketAddr,
  register_inspector_tx: UnboundedSender<InspectorInfo>,
  shutdown_server_tx: Option<oneshot::Sender<()>>,
  thread_handle: Option<thread::JoinHandle<()>>,
}

impl InspectorServer {
  pub fn new(host: SocketAddr, name: String) -> Self {
    let (register_inspector_tx, register_inspector_rx) =
      mpsc::unbounded::<InspectorInfo>();

    let (shutdown_server_tx, shutdown_server_rx) = oneshot::channel();

    let thread_handle = thread::spawn(move || {
      let rt = crate::tokio_util::create_basic_runtime();
      let local = tokio::task::LocalSet::new();
      local.block_on(
        &rt,
        server(host, register_inspector_rx, shutdown_server_rx, name),
      )
    });

    Self {
      host,
      register_inspector_tx,
      shutdown_server_tx: Some(shutdown_server_tx),
      thread_handle: Some(thread_handle),
    }
  }

  fn register_inspector(&self, info: InspectorInfo) {
    self.register_inspector_tx.unbounded_send(info).unwrap();
  }
}

impl Drop for InspectorServer {
  fn drop(&mut self) {
    if let Some(shutdown_server_tx) = self.shutdown_server_tx.take() {
      shutdown_server_tx
        .send(())
        .expect("unable to send shutdown signal");
    }

    if let Some(thread_handle) = self.thread_handle.take() {
      thread_handle.join().expect("unable to join thread");
    }
  }
}

/// Inspector information that is sent from the isolate thread to the server
/// thread when a new inspector is created.
struct InspectorInfo {
  host: SocketAddr,
  uuid: Uuid,
  thread_name: Option<String>,
  new_websocket_tx: UnboundedSender<WebSocketProxy>,
  canary_rx: oneshot::Receiver<Never>,
}

impl InspectorInfo {
  fn get_json_metadata(&self) -> Value {
    json!({
      "description": "deno",
      "devtoolsFrontendUrl": self.get_frontend_url(),
      "faviconUrl": "https://deno.land/favicon.ico",
      "id": self.uuid.to_string(),
      "title": self.get_title(),
      "type": "deno",
      // TODO(ry): "url": "file://",
      "webSocketDebuggerUrl": self.get_websocket_debugger_url(),
    })
  }

  fn get_websocket_debugger_url(&self) -> String {
    format!("ws://{}/ws/{}", &self.host, &self.uuid)
  }

  fn get_frontend_url(&self) -> String {
    format!(
      "devtools://devtools/bundled/inspector.html?v8only=true&ws={}/ws/{}",
      &self.host, &self.uuid
    )
  }

  fn get_title(&self) -> String {
    format!(
      "[{}] deno{}",
      process::id(),
      self
        .thread_name
        .as_ref()
        .map(|n| format!(" - {}", n))
        .unwrap_or_default()
    )
  }
}

// Needed so hyper can use non Send futures
#[derive(Clone)]
struct LocalExecutor;

impl<Fut> hyper::rt::Executor<Fut> for LocalExecutor
where
  Fut: Future + 'static,
  Fut::Output: 'static,
{
  fn execute(&self, fut: Fut) {
    tokio::task::spawn_local(fut);
  }
}

fn handle_ws_request(
  req: http::Request<hyper::Body>,
  inspector_map: Rc<RefCell<HashMap<Uuid, InspectorInfo>>>,
) -> http::Result<http::Response<hyper::Body>> {
  let (parts, body) = req.into_parts();
  let req = http::Request::from_parts(parts, ());

  if let Some(new_websocket_tx) = req
    .uri()
    .path()
    .strip_prefix("/ws/")
    .and_then(|s| Uuid::parse_str(s).ok())
    .and_then(|uuid| {
      inspector_map
        .borrow()
        .get(&uuid)
        .map(|info| info.new_websocket_tx.clone())
    })
  {
    let resp = tungstenite::handshake::server::create_response(&req)
      .map(|resp| resp.map(|_| hyper::Body::empty()))
      .or_else(|e| match e {
        tungstenite::error::Error::HttpFormat(http_error) => Err(http_error),
        _ => http::Response::builder()
          .status(http::StatusCode::BAD_REQUEST)
          .body("Not a valid Websocket Request".into()),
      });

    let (parts, _) = req.into_parts();
    let req = http::Request::from_parts(parts, body);

    if resp.is_ok() {
      tokio::task::spawn_local(async move {
        let upgraded = hyper::upgrade::on(req).await.unwrap();
        let websocket =
          deno_websocket::tokio_tungstenite::WebSocketStream::from_raw_socket(
            upgraded,
            tungstenite::protocol::Role::Server,
            None,
          )
          .await;
        let (proxy, pump) = create_websocket_proxy(websocket);

        let _ = new_websocket_tx.unbounded_send(proxy);
        pump.await;
      });
    }
    resp
  } else {
    http::Response::builder()
      .status(http::StatusCode::NOT_FOUND)
      .body("No Valid inspector".into())
  }
}

fn handle_json_request(
  inspector_map: Rc<RefCell<HashMap<Uuid, InspectorInfo>>>,
) -> http::Result<http::Response<hyper::Body>> {
  let data = inspector_map
    .borrow()
    .values()
    .map(|info| info.get_json_metadata())
    .collect::<Vec<_>>();
  http::Response::builder()
    .status(http::StatusCode::OK)
    .header(http::header::CONTENT_TYPE, "application/json")
    .body(serde_json::to_string(&data).unwrap().into())
}

fn handle_json_version_request(
  version_response: Value,
) -> http::Result<http::Response<hyper::Body>> {
  http::Response::builder()
    .status(http::StatusCode::OK)
    .header(http::header::CONTENT_TYPE, "application/json")
    .body(serde_json::to_string(&version_response).unwrap().into())
}

async fn server(
  host: SocketAddr,
  register_inspector_rx: UnboundedReceiver<InspectorInfo>,
  shutdown_server_rx: oneshot::Receiver<()>,
  name: String,
) {
  let inspector_map_ =
    Rc::new(RefCell::new(HashMap::<Uuid, InspectorInfo>::new()));

  let inspector_map = Rc::clone(&inspector_map_);
  let register_inspector_handler = register_inspector_rx
    .map(|info| {
      eprintln!(
        "Debugger listening on {}",
        info.get_websocket_debugger_url()
      );
      if inspector_map.borrow_mut().insert(info.uuid, info).is_some() {
        panic!("Inspector UUID already in map");
      }
    })
    .collect::<()>();

  let inspector_map = Rc::clone(&inspector_map_);
  let deregister_inspector_handler = future::poll_fn(|cx| {
    inspector_map
      .borrow_mut()
      .retain(|_, info| info.canary_rx.poll_unpin(cx) == Poll::Pending);
    Poll::<Never>::Pending
  })
  .fuse();

  let json_version_response = json!({
    "Browser": name,
    "Protocol-Version": "1.3",
    "V8-Version": deno_core::v8_version(),
  });

  let make_svc = hyper::service::make_service_fn(|_| {
    let inspector_map = Rc::clone(&inspector_map_);
    let json_version_response = json_version_response.clone();

    future::ok::<_, Infallible>(hyper::service::service_fn(
      move |req: http::Request<hyper::Body>| {
        future::ready({
          match (req.method(), req.uri().path()) {
            (&http::Method::GET, path) if path.starts_with("/ws/") => {
              handle_ws_request(req, inspector_map.clone())
            }
            (&http::Method::GET, "/json/version") => {
              handle_json_version_request(json_version_response.clone())
            }
            (&http::Method::GET, "/json") => {
              handle_json_request(inspector_map.clone())
            }
            (&http::Method::GET, "/json/list") => {
              handle_json_request(inspector_map.clone())
            }
            _ => http::Response::builder()
              .status(http::StatusCode::NOT_FOUND)
              .body("Not Found".into()),
          }
        })
      },
    ))
  });

  // Create the server manually so it can use the Local Executor
  let server_handler = hyper::server::Builder::new(
    hyper::server::conn::AddrIncoming::bind(&host).unwrap_or_else(|e| {
      eprintln!("Cannot start inspector server: {}.", e);
      process::exit(1);
    }),
    hyper::server::conn::Http::new().with_executor(LocalExecutor),
  )
  .serve(make_svc)
  .with_graceful_shutdown(async {
    shutdown_server_rx.await.ok();
  })
  .unwrap_or_else(|err| {
    eprintln!("Cannot start inspector server: {}.", err);
    process::exit(1);
  })
  .fuse();

  pin_mut!(register_inspector_handler);
  pin_mut!(deregister_inspector_handler);
  pin_mut!(server_handler);

  select! {
    _ = register_inspector_handler => {},
    _ = deregister_inspector_handler => unreachable!(),
    _ = server_handler => {},
  }
}

type WebSocketProxySender = UnboundedSender<tungstenite::Message>;
type WebSocketProxyReceiver =
  UnboundedReceiver<Result<tungstenite::Message, tungstenite::Error>>;

/// Encapsulates an UnboundedSender/UnboundedReceiver pair that together form
/// a duplex channel for sending/receiving websocket messages.
struct WebSocketProxy {
  tx: WebSocketProxySender,
  rx: WebSocketProxyReceiver,
}

impl WebSocketProxy {
  pub fn split(self) -> (WebSocketProxySender, WebSocketProxyReceiver) {
    (self.tx, self.rx)
  }
}

/// Creates a future that proxies messages sent and received on a warp WebSocket
/// to a UnboundedSender/UnboundedReceiver pair. We need this to sidestep
/// Tokio's task budget, which causes issues when DenoInspector::poll_sessions()
/// needs to block the thread because JavaScript execution is paused.
///
/// This works because UnboundedSender/UnboundedReceiver are implemented in the
/// 'futures' crate, therefore they can't participate in Tokio's cooperative
/// task yielding.
///
/// A tuple is returned, where the first element is a duplex channel that can
/// be used to send/receive messages on the websocket, and the second element
/// is a future that does the forwarding.
fn create_websocket_proxy(
  websocket: deno_websocket::tokio_tungstenite::WebSocketStream<
    hyper::upgrade::Upgraded,
  >,
) -> (WebSocketProxy, impl Future<Output = ()> + Send) {
  // The 'outbound' channel carries messages sent to the websocket.
  let (outbound_tx, outbound_rx) = mpsc::unbounded();

  // The 'inbound' channel carries messages received from the websocket.
  let (inbound_tx, inbound_rx) = mpsc::unbounded();

  let proxy = WebSocketProxy {
    tx: outbound_tx,
    rx: inbound_rx,
  };

  // The pump future takes care of forwarding messages between the websocket
  // and channels. It resolves to () when either side disconnects, ignoring any
  // errors.
  let pump = async move {
    let (websocket_tx, websocket_rx) = websocket.split();

    let outbound_pump =
      outbound_rx.map(Ok).forward(websocket_tx).map_err(|_| ());

    let inbound_pump = websocket_rx
      .map(|msg| inbound_tx.unbounded_send(msg))
      .map_err(|_| ())
      .try_collect::<()>();

    let _ = future::try_join(outbound_pump, inbound_pump).await;
  };

  (proxy, pump)
}

#[derive(Clone, Copy)]
enum PollState {
  Idle,
  Woken,
  Polling,
  Parked,
  Dropped,
}

pub struct DenoInspector {
  v8_inspector_client: v8::inspector::V8InspectorClientBase,
  v8_inspector: v8::UniquePtr<v8::inspector::V8Inspector>,
  sessions: RefCell<InspectorSessions>,
  flags: RefCell<InspectorFlags>,
  waker: Arc<InspectorWaker>,
  _canary_tx: oneshot::Sender<Never>,
  pub server: Option<Arc<InspectorServer>>,
  pub debugger_url: Option<String>,
}

impl Deref for DenoInspector {
  type Target = v8::inspector::V8Inspector;
  fn deref(&self) -> &Self::Target {
    self.v8_inspector.as_ref().unwrap()
  }
}

impl DerefMut for DenoInspector {
  fn deref_mut(&mut self) -> &mut Self::Target {
    self.v8_inspector.as_mut().unwrap()
  }
}

impl Drop for DenoInspector {
  fn drop(&mut self) {
    // Since the  waker is cloneable, it might outlive the inspector itself.
    // Set the poll state to 'dropped' so it doesn't attempt to request an
    // interrupt from the isolate.
    self.waker.update(|w| w.poll_state = PollState::Dropped);
    // V8 automatically deletes all sessions when an Inspector instance is
    // deleted, however InspectorSession also has a drop handler that cleans
    // up after itself. To avoid a double free, make sure the inspector is
    // dropped last.
    take(&mut *self.sessions.borrow_mut());
  }
}

impl v8::inspector::V8InspectorClientImpl for DenoInspector {
  fn base(&self) -> &v8::inspector::V8InspectorClientBase {
    &self.v8_inspector_client
  }

  fn base_mut(&mut self) -> &mut v8::inspector::V8InspectorClientBase {
    &mut self.v8_inspector_client
  }

  fn run_message_loop_on_pause(&mut self, context_group_id: i32) {
    assert_eq!(context_group_id, DenoInspectorSession::CONTEXT_GROUP_ID);
    self.flags.borrow_mut().on_pause = true;
    let _ = self.poll_sessions(None);
  }

  fn quit_message_loop_on_pause(&mut self) {
    self.flags.borrow_mut().on_pause = false;
  }

  fn run_if_waiting_for_debugger(&mut self, context_group_id: i32) {
    assert_eq!(context_group_id, DenoInspectorSession::CONTEXT_GROUP_ID);
    self.flags.borrow_mut().session_handshake_done = true;
  }
}

/// DenoInspector implements a Future so that it can poll for new incoming
/// connections and messages from the WebSocket server. The Worker that owns
/// this DenoInspector will call our poll function from Worker::poll().
impl Future for DenoInspector {
  type Output = ();
  fn poll(self: Pin<&mut Self>, cx: &mut Context) -> Poll<()> {
    self.poll_sessions(Some(cx)).unwrap()
  }
}

impl DenoInspector {
  const CONTEXT_GROUP_ID: i32 = 1;

  pub fn new(
    js_runtime: &mut deno_core::JsRuntime,
    server: Option<Arc<InspectorServer>>,
  ) -> Box<Self> {
    let context = js_runtime.global_context();
    let scope = &mut v8::HandleScope::new(js_runtime.v8_isolate());

    let (new_websocket_tx, new_websocket_rx) =
      mpsc::unbounded::<WebSocketProxy>();
    let (canary_tx, canary_rx) = oneshot::channel::<Never>();

    // Create DenoInspector instance.
    let mut self_ = new_box_with(|self_ptr| {
      let v8_inspector_client =
        v8::inspector::V8InspectorClientBase::new::<Self>();

      let sessions = InspectorSessions::new(self_ptr, new_websocket_rx);
      let flags = InspectorFlags::new();
      let waker = InspectorWaker::new(scope.thread_safe_handle());

      let debugger_url = if let Some(server) = server.clone() {
        let info = InspectorInfo {
          host: server.host,
          uuid: Uuid::new_v4(),
          thread_name: thread::current().name().map(|n| n.to_owned()),
          new_websocket_tx,
          canary_rx,
        };

        let debugger_url = info.get_websocket_debugger_url();
        server.register_inspector(info);
        Some(debugger_url)
      } else {
        None
      };

      Self {
        v8_inspector_client,
        v8_inspector: Default::default(),
        sessions,
        flags,
        waker,
        _canary_tx: canary_tx,
        server,
        debugger_url,
      }
    });
    self_.v8_inspector =
      v8::inspector::V8Inspector::create(scope, &mut *self_).into();

    // Tell the inspector about the global context.
    let context = v8::Local::new(scope, context);
    let context_name = v8::inspector::StringView::from(&b"global context"[..]);
    self_.context_created(context, Self::CONTEXT_GROUP_ID, context_name);

    // Poll the session handler so we will get notified whenever there is
    // new_incoming debugger activity.
    let _ = self_.poll_sessions(None).unwrap();

    self_
  }

  fn poll_sessions(
    &self,
    mut invoker_cx: Option<&mut Context>,
  ) -> Result<Poll<()>, BorrowMutError> {
    // Short-circuit if there is no server
    if self.server.is_none() {
      return Ok(Poll::Ready(()));
    }

    // The futures this function uses do not have re-entrant poll() functions.
    // However it is can happpen that poll_sessions() gets re-entered, e.g.
    // when an interrupt request is honored while the inspector future is polled
    // by the task executor. We let the caller know by returning some error.
    let mut sessions = self.sessions.try_borrow_mut()?;

    self.waker.update(|w| {
      match w.poll_state {
        PollState::Idle | PollState::Woken => w.poll_state = PollState::Polling,
        _ => unreachable!(),
      };
    });

    // Create a new Context object that will make downstream futures
    // use the InspectorWaker when they are ready to be polled again.
    let waker_ref = task::waker_ref(&self.waker);
    let cx = &mut Context::from_waker(&waker_ref);

    loop {
      loop {
        // Do one "handshake" with a newly connected session at a time.
        if let Some(session) = &mut sessions.handshake {
          let poll_result = session.poll_unpin(cx);
          let handshake_done =
            replace(&mut self.flags.borrow_mut().session_handshake_done, false);
          match poll_result {
            Poll::Pending if handshake_done => {
              let session = sessions.handshake.take().unwrap();
              sessions.established.push(session);
              take(&mut self.flags.borrow_mut().waiting_for_session);
            }
            Poll::Ready(_) => sessions.handshake = None,
            Poll::Pending => break,
          };
        }

        // Accept new connections.
        match sessions.new_incoming.poll_next_unpin(cx) {
          Poll::Ready(Some(session)) => {
            let prev = sessions.handshake.replace(session);
            assert!(prev.is_none());
            continue;
          }
          Poll::Ready(None) => {}
          Poll::Pending => {}
        }

        // Poll established sessions.
        match sessions.established.poll_next_unpin(cx) {
          Poll::Ready(Some(_)) => continue,
          Poll::Ready(None) => break,
          Poll::Pending => break,
        };
      }

      let should_block = sessions.handshake.is_some()
        || self.flags.borrow().on_pause
        || self.flags.borrow().waiting_for_session;

      let new_state = self.waker.update(|w| {
        match w.poll_state {
          PollState::Woken => {
            // The inspector was woken while the session handler was being
            // polled, so we poll it another time.
            w.poll_state = PollState::Polling;
          }
          PollState::Polling if !should_block => {
            // The session handler doesn't need to be polled any longer, and
            // there's no reason to block (execution is not paused), so this
            // function is about to return.
            w.poll_state = PollState::Idle;
            // Register the task waker that can be used to wake the parent
            // task that will poll the inspector future.
            if let Some(cx) = invoker_cx.take() {
              w.task_waker.replace(cx.waker().clone());
            }
            // Register the address of the inspector, which allows the waker
            // to request an interrupt from the isolate.
            w.inspector_ptr = NonNull::new(self as *const _ as *mut Self);
          }
          PollState::Polling if should_block => {
            // Isolate execution has been paused but there are no more
            // events to process, so this thread will be parked. Therefore,
            // store the current thread handle in the waker so it knows
            // which thread to unpark when new events arrive.
            w.poll_state = PollState::Parked;
            w.parked_thread.replace(thread::current());
          }
          _ => unreachable!(),
        };
        w.poll_state
      });
      match new_state {
        PollState::Idle => break Ok(Poll::Pending), // Yield to task.
        PollState::Polling => {} // Poll the session handler again.
        PollState::Parked => thread::park(), // Park the thread.
        _ => unreachable!(),
      };
    }
  }

  /// This function blocks the thread until at least one inspector client has
  /// established a websocket connection and successfully completed the
  /// handshake. After that, it instructs V8 to pause at the next statement.
  pub fn wait_for_session_and_break_on_next_statement(&mut self) {
    loop {
      match self.sessions.get_mut().established.iter_mut().next() {
        Some(session) => break session.break_on_next_statement(),
        None => {
          self.flags.get_mut().waiting_for_session = true;
          let _ = self.poll_sessions(None).unwrap();
        }
      };
    }
  }
}

#[derive(Default)]
struct InspectorFlags {
  waiting_for_session: bool,
  session_handshake_done: bool,
  on_pause: bool,
}

impl InspectorFlags {
  fn new() -> RefCell<Self> {
    let self_ = Self::default();
    RefCell::new(self_)
  }
}

struct InspectorSessions {
  new_incoming:
    Pin<Box<dyn Stream<Item = Box<DenoInspectorSession>> + 'static>>,
  handshake: Option<Box<DenoInspectorSession>>,
  established: FuturesUnordered<Box<DenoInspectorSession>>,
}

impl InspectorSessions {
  fn new(
    inspector_ptr: *mut DenoInspector,
    new_websocket_rx: UnboundedReceiver<WebSocketProxy>,
  ) -> RefCell<Self> {
    let new_incoming = new_websocket_rx
      .map(move |websocket| DenoInspectorSession::new(inspector_ptr, websocket))
      .boxed_local();
    let self_ = Self {
      new_incoming,
      ..Default::default()
    };
    RefCell::new(self_)
  }
}

impl Default for InspectorSessions {
  fn default() -> Self {
    Self {
      new_incoming: stream::empty().boxed_local(),
      handshake: None,
      established: FuturesUnordered::new(),
    }
  }
}

struct InspectorWakerInner {
  poll_state: PollState,
  task_waker: Option<task::Waker>,
  parked_thread: Option<thread::Thread>,
  inspector_ptr: Option<NonNull<DenoInspector>>,
  isolate_handle: v8::IsolateHandle,
}

unsafe impl Send for InspectorWakerInner {}

struct InspectorWaker(Mutex<InspectorWakerInner>);

impl InspectorWaker {
  fn new(isolate_handle: v8::IsolateHandle) -> Arc<Self> {
    let inner = InspectorWakerInner {
      poll_state: PollState::Idle,
      task_waker: None,
      parked_thread: None,
      inspector_ptr: None,
      isolate_handle,
    };
    Arc::new(Self(Mutex::new(inner)))
  }

  fn update<F, R>(&self, update_fn: F) -> R
  where
    F: FnOnce(&mut InspectorWakerInner) -> R,
  {
    let mut g = self.0.lock().unwrap();
    update_fn(&mut g)
  }
}

impl task::ArcWake for InspectorWaker {
  fn wake_by_ref(arc_self: &Arc<Self>) {
    arc_self.update(|w| {
      match w.poll_state {
        PollState::Idle => {
          // Wake the task, if any, that has polled the Inspector future last.
          if let Some(waker) = w.task_waker.take() {
            waker.wake()
          }
          // Request an interrupt from the isolate if it's running and there's
          // not unhandled interrupt request in flight.
          if let Some(arg) = w
            .inspector_ptr
            .take()
            .map(|ptr| ptr.as_ptr() as *mut c_void)
          {
            w.isolate_handle.request_interrupt(handle_interrupt, arg);
          }
          extern "C" fn handle_interrupt(
            _isolate: &mut v8::Isolate,
            arg: *mut c_void,
          ) {
            let inspector = unsafe { &*(arg as *mut DenoInspector) };
            let _ = inspector.poll_sessions(None);
          }
        }
        PollState::Parked => {
          // Unpark the isolate thread.
          let parked_thread = w.parked_thread.take().unwrap();
          assert_ne!(parked_thread.id(), thread::current().id());
          parked_thread.unpark();
        }
        _ => {}
      };
      w.poll_state = PollState::Woken;
    });
  }
}

struct DenoInspectorSession {
  v8_channel: v8::inspector::ChannelBase,
  v8_session: v8::UniqueRef<v8::inspector::V8InspectorSession>,
  websocket_tx: WebSocketProxySender,
  websocket_rx_handler: Pin<Box<dyn Future<Output = ()> + 'static>>,
}

impl Deref for DenoInspectorSession {
  type Target = v8::inspector::V8InspectorSession;
  fn deref(&self) -> &Self::Target {
    &self.v8_session
  }
}

impl DerefMut for DenoInspectorSession {
  fn deref_mut(&mut self) -> &mut Self::Target {
    &mut self.v8_session
  }
}

impl DenoInspectorSession {
  const CONTEXT_GROUP_ID: i32 = 1;

  pub fn new(
    inspector_ptr: *mut DenoInspector,
    websocket: WebSocketProxy,
  ) -> Box<Self> {
    new_box_with(move |self_ptr| {
      let v8_channel = v8::inspector::ChannelBase::new::<Self>();
      let v8_session = unsafe { &mut *inspector_ptr }.connect(
        Self::CONTEXT_GROUP_ID,
        // Todo(piscisaureus): V8Inspector::connect() should require that
        // the 'v8_channel' argument cannot move.
        unsafe { &mut *self_ptr },
        v8::inspector::StringView::empty(),
      );

      let (websocket_tx, websocket_rx) = websocket.split();
      let websocket_rx_handler =
        Self::receive_from_websocket(self_ptr, websocket_rx);

      Self {
        v8_channel,
        v8_session,
        websocket_tx,
        websocket_rx_handler,
      }
    })
  }

  /// Returns a future that receives messages from the websocket and dispatches
  /// them to the V8 session.
  fn receive_from_websocket(
    self_ptr: *mut Self,
    websocket_rx: WebSocketProxyReceiver,
  ) -> Pin<Box<dyn Future<Output = ()> + 'static>> {
    async move {
      eprintln!("Debugger session started.");

      let result = websocket_rx
        .map_ok(move |msg| {
          let msg = msg.into_data();
          let msg = v8::inspector::StringView::from(msg.as_slice());
          unsafe { &mut *self_ptr }.dispatch_protocol_message(msg);
        })
        .try_collect::<()>()
        .await;

      match result {
        Ok(_) => eprintln!("Debugger session ended."),
        Err(err) => eprintln!("Debugger session ended: {}.", err),
      };
    }
    .boxed_local()
  }

  fn send_to_websocket(&self, msg: v8::UniquePtr<v8::inspector::StringBuffer>) {
    let msg = msg.unwrap().string().to_string();
    let msg = tungstenite::Message::text(msg);
    let _ = self.websocket_tx.unbounded_send(msg);
  }

  pub fn break_on_next_statement(&mut self) {
    let reason = v8::inspector::StringView::from(&b"debugCommand"[..]);
    let detail = v8::inspector::StringView::empty();
    self.schedule_pause_on_next_statement(reason, detail);
  }
}

impl v8::inspector::ChannelImpl for DenoInspectorSession {
  fn base(&self) -> &v8::inspector::ChannelBase {
    &self.v8_channel
  }

  fn base_mut(&mut self) -> &mut v8::inspector::ChannelBase {
    &mut self.v8_channel
  }

  fn send_response(
    &mut self,
    _call_id: i32,
    message: v8::UniquePtr<v8::inspector::StringBuffer>,
  ) {
    self.send_to_websocket(message);
  }

  fn send_notification(
    &mut self,
    message: v8::UniquePtr<v8::inspector::StringBuffer>,
  ) {
    self.send_to_websocket(message);
  }

  fn flush_protocol_notifications(&mut self) {}
}

impl Future for DenoInspectorSession {
  type Output = ();
  fn poll(mut self: Pin<&mut Self>, cx: &mut Context) -> Poll<Self::Output> {
    self.websocket_rx_handler.poll_unpin(cx)
  }
}

/// A local inspector session that can be used to send and receive protocol messages directly on
/// the same thread as an isolate.
pub struct InspectorSession {
  v8_channel: v8::inspector::ChannelBase,
  v8_session: v8::UniqueRef<v8::inspector::V8InspectorSession>,
  response_tx_map: HashMap<i32, oneshot::Sender<serde_json::Value>>,
  next_message_id: i32,
  notification_queue: Vec<Value>,
}

impl Deref for InspectorSession {
  type Target = v8::inspector::V8InspectorSession;
  fn deref(&self) -> &Self::Target {
    &self.v8_session
  }
}

impl DerefMut for InspectorSession {
  fn deref_mut(&mut self) -> &mut Self::Target {
    &mut self.v8_session
  }
}

impl v8::inspector::ChannelImpl for InspectorSession {
  fn base(&self) -> &v8::inspector::ChannelBase {
    &self.v8_channel
  }

  fn base_mut(&mut self) -> &mut v8::inspector::ChannelBase {
    &mut self.v8_channel
  }

  fn send_response(
    &mut self,
    call_id: i32,
    message: v8::UniquePtr<v8::inspector::StringBuffer>,
  ) {
    let raw_message = message.unwrap().string().to_string();
    let message: serde_json::Value = match serde_json::from_str(&raw_message) {
      Ok(v) => v,
      Err(error) => match error.classify() {
        serde_json::error::Category::Syntax => json!({
          "id": call_id,
          "result": {
            "result": {
              "type": "error",
              "description": "Unterminated string literal",
              "value": "Unterminated string literal",
            },
            "exceptionDetails": {
              "exceptionId": 0,
              "text": "Unterminated string literal",
              "lineNumber": 0,
              "columnNumber": 0
            },
          },
        }),
        _ => panic!("Could not parse inspector message"),
      },
    };

    self
      .response_tx_map
      .remove(&call_id)
      .unwrap()
      .send(message)
      .unwrap();
  }

  fn send_notification(
    &mut self,
    message: v8::UniquePtr<v8::inspector::StringBuffer>,
  ) {
    let raw_message = message.unwrap().string().to_string();
    let message = serde_json::from_str(&raw_message).unwrap();

    self.notification_queue.push(message);
  }

  fn flush_protocol_notifications(&mut self) {}
}

impl InspectorSession {
  const CONTEXT_GROUP_ID: i32 = 1;

  pub fn new(inspector_ptr: *mut DenoInspector) -> Box<Self> {
    new_box_with(move |self_ptr| {
      let v8_channel = v8::inspector::ChannelBase::new::<Self>();
      let v8_session = unsafe { &mut *inspector_ptr }.connect(
        Self::CONTEXT_GROUP_ID,
        unsafe { &mut *self_ptr },
        v8::inspector::StringView::empty(),
      );

      let response_tx_map = HashMap::new();
      let next_message_id = 0;

      let notification_queue = Vec::new();

      Self {
        v8_channel,
        v8_session,
        response_tx_map,
        next_message_id,
        notification_queue,
      }
    })
  }

  pub fn notifications(&mut self) -> Vec<Value> {
    self.notification_queue.split_off(0)
  }

  pub async fn post_message(
    &mut self,
    method: &str,
    params: Option<serde_json::Value>,
  ) -> Result<serde_json::Value, AnyError> {
    let id = self.next_message_id;
    self.next_message_id += 1;

    let (response_tx, response_rx) = oneshot::channel::<serde_json::Value>();
    self.response_tx_map.insert(id, response_tx);

    let message = json!({
        "id": id,
        "method": method,
        "params": params,
    });

    let raw_message = serde_json::to_string(&message).unwrap();
    let raw_message = v8::inspector::StringView::from(raw_message.as_bytes());
    self.v8_session.dispatch_protocol_message(raw_message);

    let response = response_rx.await.unwrap();
    if let Some(error) = response.get("error") {
      return Err(generic_error(error.to_string()));
    }

    let result = response.get("result").unwrap().clone();
    Ok(result)
  }
}

fn new_box_with<T>(new_fn: impl FnOnce(*mut T) -> T) -> Box<T> {
  let b = Box::new(MaybeUninit::<T>::uninit());
  let p = Box::into_raw(b) as *mut T;
  unsafe { ptr::write(p, new_fn(p)) };
  unsafe { Box::from_raw(p) }
}