Organize dispatch a bit (#2796)

Just some clean up reorganization around flatbuffer/minimal dispatch
code. This is prep for adding a JSON dispatcher.

cli/ops/io.rs

@@ -0,0 +1,43 @@
+use super::dispatch_minimal::MinimalOp;
+use crate::deno_error;
+use crate::resources;
+use crate::tokio_write;
+use deno::ErrBox;
+use deno::PinnedBuf;
+use futures::Future;
+
+pub fn op_read(rid: i32, zero_copy: Option<PinnedBuf>) -> Box<MinimalOp> {
+  debug!("read rid={}", rid);
+  let zero_copy = match zero_copy {
+    None => {
+      return Box::new(futures::future::err(deno_error::no_buffer_specified()))
+    }
+    Some(buf) => buf,
+  };
+  match resources::lookup(rid as u32) {
+    None => Box::new(futures::future::err(deno_error::bad_resource())),
+    Some(resource) => Box::new(
+      tokio::io::read(resource, zero_copy)
+        .map_err(ErrBox::from)
+        .and_then(move |(_resource, _buf, nread)| Ok(nread as i32)),
+    ),
+  }
+}
+
+pub fn op_write(rid: i32, zero_copy: Option<PinnedBuf>) -> Box<MinimalOp> {
+  debug!("write rid={}", rid);
+  let zero_copy = match zero_copy {
+    None => {
+      return Box::new(futures::future::err(deno_error::no_buffer_specified()))
+    }
+    Some(buf) => buf,
+  };
+  match resources::lookup(rid as u32) {
+    None => Box::new(futures::future::err(deno_error::bad_resource())),
+    Some(resource) => Box::new(
+      tokio_write::write(resource, zero_copy)
+        .map_err(ErrBox::from)
+        .and_then(move |(_resource, _buf, nwritten)| Ok(nwritten as i32)),
+    ),
+  }
+}