1 files changed, 84 insertions, 0 deletions
diff --git a/core/resources.rs b/core/resources.rs
new file mode 100644
index 000000000..c3d8b7107
--- /dev/null
+++ b/core/resources.rs
@@ -0,0 +1,84 @@
+// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
+
+// Think of Resources as File Descriptors. They are integers that are allocated by
+// the privileged side of Deno to refer to various rust objects that need to be
+// referenced between multiple ops. For example, network sockets are resources.
+// Resources may or may not correspond to a real operating system file
+// descriptor (hence the different name).
+
+use downcast_rs::Downcast;
+use std;
+use std::any::Any;
+use std::collections::HashMap;
+use std::io::Error;
+use std::io::ErrorKind;
+
+/// ResourceId is Deno's version of a file descriptor. ResourceId is also referred
+/// to as rid in the code base.
+pub type ResourceId = u32;
+
+/// These store Deno's file descriptors. These are not necessarily the operating
+/// system ones.
+type ResourceMap = HashMap<ResourceId, Box<dyn Resource>>;
+
+#[derive(Default)]
+pub struct ResourceTable {
+  map: ResourceMap,
+  next_id: u32,
+}
+
+impl ResourceTable {
+  pub fn get<T: Resource>(&self, rid: ResourceId) -> Result<&T, Error> {
+    let resource = self.map.get(&rid).ok_or_else(bad_resource)?;
+    let resource = &resource.downcast_ref::<T>().ok_or_else(bad_resource)?;
+    Ok(resource)
+  }
+
+  pub fn get_mut<T: Resource>(
+    &mut self,
+    rid: ResourceId,
+  ) -> Result<&mut T, Error> {
+    let resource = self.map.get_mut(&rid).ok_or_else(bad_resource)?;
+    let resource = resource.downcast_mut::<T>().ok_or_else(bad_resource)?;
+    Ok(resource)
+  }
+
+  // TODO: resource id allocation should probably be randomized for security.
+  fn next_rid(&mut self) -> ResourceId {
+    let next_rid = self.next_id;
+    self.next_id += 1;
+    next_rid as ResourceId
+  }
+
+  pub fn add(&mut self, resource: Box<dyn Resource>) -> ResourceId {
+    let rid = self.next_rid();
+    let r = self.map.insert(rid, resource);
+    assert!(r.is_none());
+    rid
+  }
+
+  // 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) -> Result<(), Error> {
+    let repr = self.map.remove(&rid).ok_or_else(bad_resource)?;
+    // Give resource a chance to cleanup (notify tasks, etc.)
+    repr.close();
+    Ok(())
+  }
+}
+
+/// Abstract type representing resource in Deno.
+pub trait Resource: Downcast + Any + Send {
+  /// Method that allows to cleanup resource.
+  fn close(&self) {}
+
+  fn inspect_repr(&self) -> &str {
+    unimplemented!();
+  }
+}
+impl_downcast!(Resource);
+
+// TODO: probably bad error kind
+pub fn bad_resource() -> Error {
+  Error::new(ErrorKind::NotFound, "bad resource id")
+}