Add `seek` and implement `Seeker` on `File` (#1797)

This patch contains a special hack that circumvents the current tokio
seek problem.

tokio `seek` is implemented to take ownership of the original File and
emit a new one in its future, which conflicts with the design of
ResourceTable.

To avoid the problem, the current hack makes the FsFile resource
an Option which we could `take` the value ownership out of it. We then
convert the tokio File into a Rust std File, perform the seek, and then
put it back into the resource.

This might be able to drop this hack after
https://github.com/tokio-rs/tokio/pull/785 lands.

1 files changed, 23 insertions, 0 deletions

diff --git a/src/ops.rs b/src/ops.rs
index a415d7100..c8a005601 100644
--- a/src/ops.rs
+++ b/src/ops.rs
@@ -126,6 +126,7 @@ pub fn dispatch(
       msg::Any::WriteFile => op_write_file,
       msg::Any::Now => op_now,
       msg::Any::IsTTY => op_is_tty,
+      msg::Any::Seek => op_seek,
       _ => panic!(format!(
         "Unhandled message {}",
         msg::enum_name_any(inner_type)
@@ -868,6 +869,28 @@ fn op_write(
   }
 }
 
+fn op_seek(
+  _state: &Arc<IsolateState>,
+  base: &msg::Base<'_>,
+  data: libdeno::deno_buf,
+) -> Box<Op> {
+  assert_eq!(data.len(), 0);
+  let _cmd_id = base.cmd_id();
+  let inner = base.inner_as_seek().unwrap();
+  let rid = inner.rid();
+  let offset = inner.offset();
+  let whence = inner.whence();
+
+  match resources::lookup(rid) {
+    None => odd_future(errors::bad_resource()),
+    Some(resource) => {
+      let op = resources::seek(resource, offset, whence)
+        .and_then(move |_| Ok(empty_buf()));
+      Box::new(op)
+    }
+  }
+}
+
 fn op_remove(
   state: &Arc<IsolateState>,
   base: &msg::Base<'_>,