refactor: rewrite accept resources (#3271)

cli/ops/net.rs

@@ -1,16 +1,20 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 use super::dispatch_json::{Deserialize, JsonOp, Value};
+use crate::deno_error::bad_resource;
 use crate::ops::json_op;
 use crate::resolve_addr::resolve_addr;
 use crate::resources;
+use crate::resources::CoreResource;
 use crate::resources::Resource;
 use crate::state::ThreadSafeState;
-use crate::tokio_util;
 use deno::*;
+use futures::Async;
 use futures::Future;
+use futures::Poll;
 use std;
 use std::convert::From;
 use std::net::Shutdown;
+use std::net::SocketAddr;
 use tokio;
 use tokio::net::TcpListener;
 use tokio::net::TcpStream;
@@ -22,6 +26,90 @@ pub fn init(i: &mut Isolate, s: &ThreadSafeState) {
   i.register_op("listen", s.core_op(json_op(s.stateful_op(op_listen))));
 }
 
+#[derive(Debug, PartialEq)]
+enum AcceptState {
+  Eager,
+  Pending,
+  Done,
+}
+
+/// Simply accepts a connection.
+pub fn accept(rid: ResourceId) -> Accept {
+  Accept {
+    state: AcceptState::Eager,
+    rid,
+  }
+}
+
+/// A future representing state of accepting a TCP connection.
+#[derive(Debug)]
+pub struct Accept {
+  state: AcceptState,
+  rid: ResourceId,
+}
+
+impl Future for Accept {
+  type Item = (TcpStream, SocketAddr);
+  type Error = ErrBox;
+
+  fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+    if self.state == AcceptState::Done {
+      panic!("poll Accept after it's done");
+    }
+
+    let mut table = resources::lock_resource_table();
+    let listener_resource = table
+      .get_mut::<TcpListenerResource>(self.rid)
+      .ok_or_else(|| {
+        let e = std::io::Error::new(
+          std::io::ErrorKind::Other,
+          "Listener has been closed",
+        );
+        ErrBox::from(e)
+      })?;
+
+    let listener = &mut listener_resource.listener;
+
+    if self.state == AcceptState::Eager {
+      // Similar to try_ready!, but also track/untrack accept task
+      // in TcpListener resource.
+      // In this way, when the listener is closed, the task can be
+      // notified to error out (instead of stuck forever).
+      match listener.poll_accept().map_err(ErrBox::from) {
+        Ok(Async::Ready((stream, addr))) => {
+          self.state = AcceptState::Done;
+          return Ok((stream, addr).into());
+        }
+        Ok(Async::NotReady) => {
+          self.state = AcceptState::Pending;
+          return Ok(Async::NotReady);
+        }
+        Err(e) => {
+          self.state = AcceptState::Done;
+          return Err(e);
+        }
+      }
+    }
+
+    match listener.poll_accept().map_err(ErrBox::from) {
+      Ok(Async::Ready((stream, addr))) => {
+        listener_resource.untrack_task();
+        self.state = AcceptState::Done;
+        Ok((stream, addr).into())
+      }
+      Ok(Async::NotReady) => {
+        listener_resource.track_task()?;
+        Ok(Async::NotReady)
+      }
+      Err(e) => {
+        listener_resource.untrack_task();
+        self.state = AcceptState::Done;
+        Err(e)
+      }
+    }
+  }
+}
+
 #[derive(Deserialize)]
 struct AcceptArgs {
   rid: i32,
@@ -33,10 +121,14 @@ fn op_accept(
   _zero_copy: Option<PinnedBuf>,
 ) -> Result<JsonOp, ErrBox> {
   let args: AcceptArgs = serde_json::from_value(args)?;
-  let server_rid = args.rid as u32;
+  let rid = args.rid as u32;
 
-  let server_resource = resources::lookup(server_rid)?;
-  let op = tokio_util::accept(server_resource)
+  let table = resources::lock_resource_table();
+  table
+    .get::<TcpListenerResource>(rid)
+    .ok_or_else(bad_resource)?;
+
+  let op = accept(rid)
     .and_then(move |(tcp_stream, _socket_addr)| {
       let local_addr = tcp_stream.local_addr()?;
       let remote_addr = tcp_stream.peer_addr()?;
@@ -129,6 +221,59 @@ struct ListenArgs {
   port: u16,
 }
 
+#[allow(dead_code)]
+struct TcpListenerResource {
+  listener: tokio::net::TcpListener,
+  task: Option<futures::task::Task>,
+  local_addr: SocketAddr,
+}
+
+impl CoreResource for TcpListenerResource {}
+
+impl Drop for TcpListenerResource {
+  fn drop(&mut self) {
+    self.notify_task();
+  }
+}
+
+impl TcpListenerResource {
+  /// Track the current task so future awaiting for connection
+  /// can be notified when listener is closed.
+  ///
+  /// Throws an error if another task is already tracked.
+  pub fn track_task(&mut self) -> Result<(), ErrBox> {
+    // Currently, we only allow tracking a single accept task for a listener.
+    // This might be changed in the future with multiple workers.
+    // Caveat: TcpListener by itself also only tracks an accept task at a time.
+    // See https://github.com/tokio-rs/tokio/issues/846#issuecomment-454208883
+    if self.task.is_some() {
+      let e = std::io::Error::new(
+        std::io::ErrorKind::Other,
+        "Another accept task is ongoing",
+      );
+      return Err(ErrBox::from(e));
+    }
+
+    self.task.replace(futures::task::current());
+    Ok(())
+  }
+
+  /// Notifies a task when listener is closed so accept future can resolve.
+  pub fn notify_task(&mut self) {
+    if let Some(task) = self.task.take() {
+      task.notify();
+    }
+  }
+
+  /// Stop tracking a task.
+  /// Happens when the task is done and thus no further tracking is needed.
+  pub fn untrack_task(&mut self) {
+    if self.task.is_some() {
+      self.task.take();
+    }
+  }
+}
+
 fn op_listen(
   state: &ThreadSafeState,
   args: Value,
@@ -142,10 +287,17 @@ fn op_listen(
   let addr = resolve_addr(&args.hostname, args.port).wait()?;
   let listener = TcpListener::bind(&addr)?;
   let local_addr = listener.local_addr()?;
-  let resource = resources::add_tcp_listener(listener);
+  let local_addr_str = local_addr.to_string();
+  let listener_resource = TcpListenerResource {
+    listener,
+    task: None,
+    local_addr,
+  };
+  let mut table = resources::lock_resource_table();
+  let rid = table.add("tcpListener", Box::new(listener_resource));
 
   Ok(JsonOp::Sync(json!({
-    "rid": resource.rid,
-    "localAddr": local_addr.to_string()
+    "rid": rid,
+    "localAddr": local_addr_str,
   })))
 }

cli/ops/tls.rs

@@ -1,18 +1,22 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 use super::dispatch_json::{Deserialize, JsonOp, Value};
+use crate::deno_error::bad_resource;
 use crate::deno_error::DenoError;
 use crate::deno_error::ErrorKind;
 use crate::ops::json_op;
 use crate::resolve_addr::resolve_addr;
 use crate::resources;
+use crate::resources::CoreResource;
 use crate::state::ThreadSafeState;
-use crate::tokio_util;
 use deno::*;
+use futures::Async;
 use futures::Future;
+use futures::Poll;
 use std;
 use std::convert::From;
 use std::fs::File;
 use std::io::BufReader;
+use std::net::SocketAddr;
 use std::sync::Arc;
 use tokio;
 use tokio::net::TcpListener;
@@ -167,6 +171,60 @@ fn load_keys(path: &str) -> Result<Vec<PrivateKey>, ErrBox> {
   Ok(keys)
 }
 
+#[allow(dead_code)]
+pub struct TlsListenerResource {
+  listener: tokio::net::TcpListener,
+  tls_acceptor: TlsAcceptor,
+  task: Option<futures::task::Task>,
+  local_addr: SocketAddr,
+}
+
+impl CoreResource for TlsListenerResource {}
+
+impl Drop for TlsListenerResource {
+  fn drop(&mut self) {
+    self.notify_task();
+  }
+}
+
+impl TlsListenerResource {
+  /// Track the current task so future awaiting for connection
+  /// can be notified when listener is closed.
+  ///
+  /// Throws an error if another task is already tracked.
+  pub fn track_task(&mut self) -> Result<(), ErrBox> {
+    // Currently, we only allow tracking a single accept task for a listener.
+    // This might be changed in the future with multiple workers.
+    // Caveat: TcpListener by itself also only tracks an accept task at a time.
+    // See https://github.com/tokio-rs/tokio/issues/846#issuecomment-454208883
+    if self.task.is_some() {
+      let e = std::io::Error::new(
+        std::io::ErrorKind::Other,
+        "Another accept task is ongoing",
+      );
+      return Err(ErrBox::from(e));
+    }
+
+    self.task.replace(futures::task::current());
+    Ok(())
+  }
+
+  /// Notifies a task when listener is closed so accept future can resolve.
+  pub fn notify_task(&mut self) {
+    if let Some(task) = self.task.take() {
+      task.notify();
+    }
+  }
+
+  /// Stop tracking a task.
+  /// Happens when the task is done and thus no further tracking is needed.
+  pub fn untrack_task(&mut self) {
+    if self.task.is_some() {
+      self.task.take();
+    }
+  }
+}
+
 #[derive(Deserialize)]
 #[serde(rename_all = "camelCase")]
 struct ListenTlsArgs {
@@ -196,18 +254,110 @@ fn op_listen_tls(
   config
     .set_single_cert(load_certs(&cert_file)?, load_keys(&key_file)?.remove(0))
     .expect("invalid key or certificate");
-  let acceptor = TlsAcceptor::from(Arc::new(config));
+  let tls_acceptor = TlsAcceptor::from(Arc::new(config));
   let addr = resolve_addr(&args.hostname, args.port).wait()?;
   let listener = TcpListener::bind(&addr)?;
   let local_addr = listener.local_addr()?;
-  let resource = resources::add_tls_listener(listener, acceptor);
+  let local_addr_str = local_addr.to_string();
+  let tls_listener_resource = TlsListenerResource {
+    listener,
+    tls_acceptor,
+    task: None,
+    local_addr,
+  };
+  let mut table = resources::lock_resource_table();
+  let rid = table.add("tlsListener", Box::new(tls_listener_resource));
 
   Ok(JsonOp::Sync(json!({
-    "rid": resource.rid,
-    "localAddr": local_addr.to_string()
+    "rid": rid,
+    "localAddr": local_addr_str
   })))
 }
 
+#[derive(Debug, PartialEq)]
+enum AcceptTlsState {
+  Eager,
+  Pending,
+  Done,
+}
+
+/// Simply accepts a TLS connection.
+pub fn accept_tls(rid: ResourceId) -> AcceptTls {
+  AcceptTls {
+    state: AcceptTlsState::Eager,
+    rid,
+  }
+}
+
+/// A future representing state of accepting a TLS connection.
+#[derive(Debug)]
+pub struct AcceptTls {
+  state: AcceptTlsState,
+  rid: ResourceId,
+}
+
+impl Future for AcceptTls {
+  type Item = (TcpStream, SocketAddr);
+  type Error = ErrBox;
+
+  fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
+    if self.state == AcceptTlsState::Done {
+      panic!("poll AcceptTls after it's done");
+    }
+
+    let mut table = resources::lock_resource_table();
+    let listener_resource = table
+      .get_mut::<TlsListenerResource>(self.rid)
+      .ok_or_else(|| {
+        let e = std::io::Error::new(
+          std::io::ErrorKind::Other,
+          "Listener has been closed",
+        );
+        ErrBox::from(e)
+      })?;
+
+    let listener = &mut listener_resource.listener;
+
+    if self.state == AcceptTlsState::Eager {
+      // Similar to try_ready!, but also track/untrack accept task
+      // in TcpListener resource.
+      // In this way, when the listener is closed, the task can be
+      // notified to error out (instead of stuck forever).
+      match listener.poll_accept().map_err(ErrBox::from) {
+        Ok(Async::Ready((stream, addr))) => {
+          self.state = AcceptTlsState::Done;
+          return Ok((stream, addr).into());
+        }
+        Ok(Async::NotReady) => {
+          self.state = AcceptTlsState::Pending;
+          return Ok(Async::NotReady);
+        }
+        Err(e) => {
+          self.state = AcceptTlsState::Done;
+          return Err(e);
+        }
+      }
+    }
+
+    match listener.poll_accept().map_err(ErrBox::from) {
+      Ok(Async::Ready((stream, addr))) => {
+        listener_resource.untrack_task();
+        self.state = AcceptTlsState::Done;
+        Ok((stream, addr).into())
+      }
+      Ok(Async::NotReady) => {
+        listener_resource.track_task()?;
+        Ok(Async::NotReady)
+      }
+      Err(e) => {
+        listener_resource.untrack_task();
+        self.state = AcceptTlsState::Done;
+        Err(e)
+      }
+    }
+  }
+}
+
 #[derive(Deserialize)]
 struct AcceptTlsArgs {
   rid: i32,
@@ -219,26 +369,31 @@ fn op_accept_tls(
   _zero_copy: Option<PinnedBuf>,
 ) -> Result<JsonOp, ErrBox> {
   let args: AcceptTlsArgs = serde_json::from_value(args)?;
-  let server_rid = args.rid as u32;
+  let rid = args.rid as u32;
 
-  let server_resource = resources::lookup(server_rid)?;
-  let op = tokio_util::accept(server_resource)
+  let op = accept_tls(rid)
     .and_then(move |(tcp_stream, _socket_addr)| {
       let local_addr = tcp_stream.local_addr()?;
       let remote_addr = tcp_stream.peer_addr()?;
       Ok((tcp_stream, local_addr, remote_addr))
     })
     .and_then(move |(tcp_stream, local_addr, remote_addr)| {
-      let mut server_resource = resources::lookup(server_rid).unwrap();
-      server_resource
-        .poll_accept_tls(tcp_stream)
+      let table = resources::lock_resource_table();
+      let resource = table
+        .get::<TlsListenerResource>(rid)
+        .ok_or_else(bad_resource)
+        .expect("Can't find tls listener");
+
+      resource
+        .tls_acceptor
+        .accept(tcp_stream)
+        .map_err(ErrBox::from)
         .and_then(move |tls_stream| {
           let tls_stream_resource =
             resources::add_server_tls_stream(tls_stream);
           Ok((tls_stream_resource, local_addr, remote_addr))
         })
     })
-    .map_err(ErrBox::from)
     .and_then(move |(tls_stream_resource, local_addr, remote_addr)| {
       futures::future::ok(json!({
         "rid": tls_stream_resource.rid,

cli/resources.rs

@@ -21,8 +21,8 @@ use futures::Future;
 use futures::Poll;
 use reqwest::r#async::Decoder as ReqwestDecoder;
 use std;
-use std::io::{Error, Read, Seek, SeekFrom, Write};
-use std::net::{Shutdown, SocketAddr};
+use std::io::{Read, Seek, SeekFrom, Write};
+use std::net::Shutdown;
 use std::process::ExitStatus;
 use std::sync::Mutex;
 use std::sync::MutexGuard;
@@ -32,12 +32,10 @@ use tokio::net::TcpStream;
 use tokio_process;
 use tokio_rustls::client::TlsStream as ClientTlsStream;
 use tokio_rustls::server::TlsStream as ServerTlsStream;
-use tokio_rustls::TlsAcceptor;
 
 #[cfg(not(windows))]
 use std::os::unix::io::FromRawFd;
 
-use futures::future::Either;
 #[cfg(windows)]
 use std::os::windows::io::FromRawHandle;
 
@@ -73,17 +71,6 @@ enum CliResource {
   Stdout(tokio::fs::File),
   Stderr(tokio::io::Stderr),
   FsFile(tokio::fs::File),
-  // Since TcpListener might be closed while there is a pending accept task,
-  // we need to track the task so that when the listener is closed,
-  // this pending task could be notified and die.
-  // Currently TcpListener itself does not take care of this issue.
-  // See: https://github.com/tokio-rs/tokio/issues/846
-  TcpListener(tokio::net::TcpListener, Option<futures::task::Task>),
-  TlsListener(
-    tokio::net::TcpListener,
-    TlsAcceptor,
-    Option<futures::task::Task>,
-  ),
   TcpStream(tokio::net::TcpStream),
   ServerTlsStream(Box<ServerTlsStream<TcpStream>>),
   ClientTlsStream(Box<ClientTlsStream<TcpStream>>),
@@ -97,22 +84,7 @@ enum CliResource {
   ChildStderr(tokio_process::ChildStderr),
 }
 
-impl CoreResource for CliResource {
-  // TODO(ry) These task notifications are hacks to workaround various behaviors
-  // in Tokio. They should not influence the overall design of Deno. The
-  // CoreResource::close should be removed in favor of the drop trait.
-  fn close(&self) {
-    match self {
-      CliResource::TcpListener(_, Some(t)) => {
-        t.notify();
-      }
-      CliResource::TlsListener(_, _, Some(t)) => {
-        t.notify();
-      }
-      _ => {}
-    }
-  }
-}
+impl CoreResource for CliResource {}
 
 pub fn lock_resource_table<'a>() -> MutexGuard<'a, ResourceTable> {
   RESOURCE_TABLE.lock().unwrap()
@@ -126,78 +98,6 @@ pub struct Resource {
 }
 
 impl Resource {
-  // TODO Should it return a Resource instead of net::TcpStream?
-  pub fn poll_accept(&mut self) -> Poll<(TcpStream, SocketAddr), Error> {
-    let mut table = lock_resource_table();
-    match table.get_mut::<CliResource>(self.rid) {
-      None => Err(std::io::Error::new(
-        std::io::ErrorKind::Other,
-        "Listener has been closed",
-      )),
-      Some(repr) => match repr {
-        CliResource::TcpListener(ref mut s, _) => s.poll_accept(),
-        CliResource::TlsListener(ref mut s, _, _) => s.poll_accept(),
-        _ => panic!("Cannot accept"),
-      },
-    }
-  }
-
-  pub fn poll_accept_tls(
-    &mut self,
-    tcp_stream: TcpStream,
-  ) -> impl Future<Item = ServerTlsStream<TcpStream>, Error = Error> {
-    let mut table = lock_resource_table();
-    match table.get_mut::<CliResource>(self.rid) {
-      None => Either::A(futures::future::err(std::io::Error::new(
-        std::io::ErrorKind::Other,
-        "Listener has been closed",
-      ))),
-      Some(repr) => match repr {
-        CliResource::TlsListener(_, ref mut acceptor, _) => {
-          Either::B(acceptor.accept(tcp_stream))
-        }
-        _ => panic!("Cannot accept"),
-      },
-    }
-  }
-
-  /// Track the current task (for TcpListener resource).
-  /// Throws an error if another task is already tracked.
-  pub fn track_task(&mut self) -> Result<(), std::io::Error> {
-    let mut table = lock_resource_table();
-    // Only track if is TcpListener.
-    if let Some(CliResource::TcpListener(_, t)) =
-      table.get_mut::<CliResource>(self.rid)
-    {
-      // Currently, we only allow tracking a single accept task for a listener.
-      // This might be changed in the future with multiple workers.
-      // Caveat: TcpListener by itself also only tracks an accept task at a time.
-      // See https://github.com/tokio-rs/tokio/issues/846#issuecomment-454208883
-      if t.is_some() {
-        return Err(std::io::Error::new(
-          std::io::ErrorKind::Other,
-          "Another accept task is ongoing",
-        ));
-      }
-      t.replace(futures::task::current());
-    }
-    Ok(())
-  }
-
-  /// Stop tracking a task (for TcpListener resource).
-  /// Happens when the task is done and thus no further tracking is needed.
-  pub fn untrack_task(&mut self) {
-    let mut table = lock_resource_table();
-    // Only untrack if is TcpListener.
-    if let Some(CliResource::TcpListener(_, t)) =
-      table.get_mut::<CliResource>(self.rid)
-    {
-      if t.is_some() {
-        t.take();
-      }
-    }
-  }
-
   // close(2) is done by dropping the value. Therefore we just need to remove
   // the resource from the RESOURCE_TABLE.
   pub fn close(&self) {
@@ -307,27 +207,6 @@ pub fn add_fs_file(fs_file: tokio::fs::File) -> Resource {
   Resource { rid }
 }
 
-pub fn add_tcp_listener(listener: tokio::net::TcpListener) -> Resource {
-  let mut table = lock_resource_table();
-  let rid = table.add(
-    "tcpListener",
-    Box::new(CliResource::TcpListener(listener, None)),
-  );
-  Resource { rid }
-}
-
-pub fn add_tls_listener(
-  listener: tokio::net::TcpListener,
-  acceptor: TlsAcceptor,
-) -> Resource {
-  let mut table = lock_resource_table();
-  let rid = table.add(
-    "tlsListener",
-    Box::new(CliResource::TlsListener(listener, acceptor, None)),
-  );
-  Resource { rid }
-}
-
 pub fn add_tcp_stream(stream: tokio::net::TcpStream) -> Resource {
   let mut table = lock_resource_table();
   let rid = table.add("tcpStream", Box::new(CliResource::TcpStream(stream)));

cli/tokio_util.rs

@@ -1,15 +1,10 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-use crate::resources::Resource;
 use deno::ErrBox;
 use futures;
 use futures::Future;
 use futures::Poll;
-use std::io;
-use std::mem;
-use std::net::SocketAddr;
 use std::ops::FnOnce;
 use tokio;
-use tokio::net::TcpStream;
 use tokio::runtime;
 
 pub fn create_threadpool_runtime(
@@ -77,74 +72,6 @@ where
   tokio_executor::with_default(&mut executor, &mut enter, move |_enter| f());
 }
 
-#[derive(Debug)]
-enum AcceptState {
-  Eager(Resource),
-  Pending(Resource),
-  Empty,
-}
-
-/// Simply accepts a connection.
-pub fn accept(r: Resource) -> Accept {
-  Accept {
-    state: AcceptState::Eager(r),
-  }
-}
-
-/// A future which can be used to easily read available number of bytes to fill
-/// a buffer.
-///
-/// Created by the [`read`] function.
-#[derive(Debug)]
-pub struct Accept {
-  state: AcceptState,
-}
-
-impl Future for Accept {
-  type Item = (TcpStream, SocketAddr);
-  type Error = io::Error;
-
-  fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
-    let (stream, addr) = match self.state {
-      // Similar to try_ready!, but also track/untrack accept task
-      // in TcpListener resource.
-      // In this way, when the listener is closed, the task can be
-      // notified to error out (instead of stuck forever).
-      AcceptState::Eager(ref mut r) => match r.poll_accept() {
-        Ok(futures::prelude::Async::Ready(t)) => t,
-        Ok(futures::prelude::Async::NotReady) => {
-          self.state = AcceptState::Pending(r.to_owned());
-          return Ok(futures::prelude::Async::NotReady);
-        }
-        Err(e) => {
-          return Err(e);
-        }
-      },
-      AcceptState::Pending(ref mut r) => match r.poll_accept() {
-        Ok(futures::prelude::Async::Ready(t)) => {
-          r.untrack_task();
-          t
-        }
-        Ok(futures::prelude::Async::NotReady) => {
-          // Would error out if another accept task is being tracked.
-          r.track_task()?;
-          return Ok(futures::prelude::Async::NotReady);
-        }
-        Err(e) => {
-          r.untrack_task();
-          return Err(e);
-        }
-      },
-      AcceptState::Empty => panic!("poll Accept after it's done"),
-    };
-
-    match mem::replace(&mut self.state, AcceptState::Empty) {
-      AcceptState::Empty => panic!("invalid internal state"),
-      _ => Ok((stream, addr).into()),
-    }
-  }
-}
-
 /// `futures::future::poll_fn` only support `F: FnMut()->Poll<T, E>`
 /// However, we require that `F: FnOnce()->Poll<T, E>`.
 /// Therefore, we created our version of `poll_fn`.

core/resources.rs

@@ -69,18 +69,14 @@ impl ResourceTable {
   // close(2) is done by dropping the value. Therefore we just need to remove
   // the resource from the RESOURCE_TABLE.
   pub fn close(&mut self, rid: ResourceId) -> Option<()> {
-    if let Some((_name, resource)) = self.map.remove(&rid) {
-      resource.close();
-      return Some(());
-    }
-    None
+    self.map.remove(&rid).map(|(_name, _resource)| ())
   }
 }
 
 /// Abstract type representing resource in Deno.
-pub trait Resource: Downcast + Any + Send {
-  /// Method that allows to cleanup resource.
-  // TODO(ry) remove this method. Resources should rely on drop trait instead.
-  fn close(&self) {}
-}
+///
+/// The only thing it does is implementing `Downcast` trait
+/// that allows to cast resource to concrete type in `TableResource::get`
+/// and `TableResource::get_mut` methods.
+pub trait Resource: Downcast + Any + Send {}
 impl_downcast!(Resource);