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.

js/deno.ts

@@ -11,6 +11,7 @@ export {
   stderr,
   read,
   write,
+  seek,
   close,
   OpenMode
 } from "./files";
@@ -18,6 +19,7 @@ export {
   copy,
   toAsyncIterator,
   ReadResult,
+  SeekMode,
   Reader,
   Writer,
   Closer,

js/files.ts

@@ -1,12 +1,12 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import { Reader, Writer, Closer, ReadResult } from "./io";
+import { Reader, Writer, Seeker, Closer, ReadResult, SeekMode } from "./io";
 import * as dispatch from "./dispatch";
 import * as msg from "gen/msg_generated";
 import { assert } from "./util";
 import * as flatbuffers from "./flatbuffers";
 
 /** The Deno abstraction for reading and writing files. */
-export class File implements Reader, Writer, Closer {
+export class File implements Reader, Writer, Seeker, Closer {
   constructor(readonly rid: number) {}
 
   write(p: Uint8Array): Promise<number> {
@@ -17,6 +17,10 @@ export class File implements Reader, Writer, Closer {
     return read(this.rid, p);
   }
 
+  seek(offset: number, whence: SeekMode): Promise<void> {
+    return seek(this.rid, offset, whence);
+  }
+
   close(): void {
     close(this.rid);
   }
@@ -123,6 +127,23 @@ export async function write(rid: number, p: Uint8Array): Promise<number> {
   return res.nbyte();
 }
 
+/** Seek a file ID to the given offset under mode given by `whence`.
+ *
+ */
+export async function seek(
+  rid: number,
+  offset: number,
+  whence: SeekMode
+): Promise<void> {
+  const builder = flatbuffers.createBuilder();
+  msg.Seek.startSeek(builder);
+  msg.Seek.addRid(builder, rid);
+  msg.Seek.addOffset(builder, offset);
+  msg.Seek.addWhence(builder, whence);
+  const inner = msg.Seek.endSeek(builder);
+  await dispatch.sendAsync(builder, msg.Any.Seek, inner);
+}
+
 /** Close the file ID. */
 export function close(rid: number): void {
   const builder = flatbuffers.createBuilder();

js/files_test.ts

@@ -141,15 +141,61 @@ testPerm({ read: true, write: true }, async function openModeWriteRead() {
   fileInfo = Deno.statSync(filename);
   assertEqual(fileInfo.len, 13);
 
-  // TODO: this test is not working, I expect because
-  //  file handle points to the end of file, but ATM
-  //  deno has no seek implementation on Rust side
-  // assert file can be read
-  // const buf = new Uint8Array(20);
-  // const result = await file.read(buf);
-  // console.log(result.eof, result.nread);
-  // assertEqual(result.nread, 13);
-  // file.close();
+  const buf = new Uint8Array(20);
+  await file.seek(0, Deno.SeekMode.SEEK_START);
+  const result = await file.read(buf);
+  assertEqual(result.nread, 13);
+  file.close();
 
   await Deno.remove(tempDir, { recursive: true });
 });
+
+testPerm({ read: true }, async function seekStart() {
+  const filename = "tests/hello.txt";
+  const file = await Deno.open(filename);
+  // Deliberately move 1 step forward
+  await file.read(new Uint8Array(1)); // "H"
+  // Skipping "Hello "
+  await file.seek(6, Deno.SeekMode.SEEK_START);
+  const buf = new Uint8Array(6);
+  await file.read(buf);
+  const decoded = new TextDecoder().decode(buf);
+  assertEqual(decoded, "world!");
+});
+
+testPerm({ read: true }, async function seekCurrent() {
+  const filename = "tests/hello.txt";
+  const file = await Deno.open(filename);
+  // Deliberately move 1 step forward
+  await file.read(new Uint8Array(1)); // "H"
+  // Skipping "ello "
+  await file.seek(5, Deno.SeekMode.SEEK_CURRENT);
+  const buf = new Uint8Array(6);
+  await file.read(buf);
+  const decoded = new TextDecoder().decode(buf);
+  assertEqual(decoded, "world!");
+});
+
+testPerm({ read: true }, async function seekEnd() {
+  const filename = "tests/hello.txt";
+  const file = await Deno.open(filename);
+  await file.seek(-6, Deno.SeekMode.SEEK_END);
+  const buf = new Uint8Array(6);
+  await file.read(buf);
+  const decoded = new TextDecoder().decode(buf);
+  assertEqual(decoded, "world!");
+});
+
+testPerm({ read: true }, async function seekMode() {
+  const filename = "tests/hello.txt";
+  const file = await Deno.open(filename);
+  let err;
+  try {
+    await file.seek(1, -1);
+  } catch (e) {
+    err = e;
+  }
+  assert(!!err);
+  assertEqual(err.kind, Deno.ErrorKind.InvalidSeekMode);
+  assertEqual(err.name, "InvalidSeekMode");
+});

js/io.ts

@@ -9,6 +9,14 @@ export interface ReadResult {
   eof: boolean;
 }
 
+// Seek whence values.
+// https://golang.org/pkg/io/#pkg-constants
+export enum SeekMode {
+  SEEK_START = 0,
+  SEEK_CURRENT = 1,
+  SEEK_END = 2
+}
+
 // Reader is the interface that wraps the basic read() method.
 // https://golang.org/pkg/io/#Reader
 export interface Reader {
@@ -74,7 +82,7 @@ export interface Seeker {
    * any positive offset is legal, but the behavior of subsequent I/O operations
    * on the underlying object is implementation-dependent.
    */
-  seek(offset: number, whence: number): Promise<void>;
+  seek(offset: number, whence: SeekMode): Promise<void>;
 }
 
 // https://golang.org/pkg/io/#ReadCloser

src/msg.fbs

@@ -65,6 +65,7 @@ union Any {
   NowRes,
   IsTTY,
   IsTTYRes,
+  Seek,
 }
 
 enum ErrorKind: byte {
@@ -117,6 +118,7 @@ enum ErrorKind: byte {
 
   // custom errors
   InvalidUri,
+  InvalidSeekMode,
 }
 
 table Cwd {}
@@ -496,4 +498,10 @@ table IsTTYRes {
   stderr: bool;
 }
 
+table Seek {
+  rid: uint32;
+  offset: int;
+  whence: uint;
+}
+
 root_type Base;

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<'_>,

src/resources.rs

@@ -30,7 +30,7 @@ use futures::Stream;
 use hyper;
 use std;
 use std::collections::HashMap;
-use std::io::{Error, Read, Write};
+use std::io::{Error, Read, Seek, SeekFrom, Write};
 use std::net::{Shutdown, SocketAddr};
 use std::process::ExitStatus;
 use std::sync::atomic::AtomicUsize;
@@ -565,3 +565,62 @@ pub fn eager_accept(resource: Resource) -> EagerAccept {
     },
   }
 }
+
+// TODO(kevinkassimo): revamp this after the following lands:
+// https://github.com/tokio-rs/tokio/pull/785
+pub fn seek(
+  resource: Resource,
+  offset: i32,
+  whence: u32,
+) -> Box<dyn Future<Item = (), Error = DenoError> + Send> {
+  let mut table = RESOURCE_TABLE.lock().unwrap();
+  // We take ownership of File here.
+  // It is put back below while still holding the lock.
+  let maybe_repr = table.remove(&resource.rid);
+  match maybe_repr {
+    None => panic!("bad rid"),
+    Some(Repr::FsFile(f)) => {
+      let seek_from = match whence {
+        0 => SeekFrom::Start(offset as u64),
+        1 => SeekFrom::Current(offset as i64),
+        2 => SeekFrom::End(offset as i64),
+        _ => {
+          return Box::new(futures::future::err(errors::new(
+            errors::ErrorKind::InvalidSeekMode,
+            format!("Invalid seek mode: {}", whence),
+          )));
+        }
+      };
+      // Trait Clone not implemented on tokio::fs::File,
+      // so convert to std File first.
+      let std_file = f.into_std();
+      // Create a copy and immediately put back.
+      // We don't want to block other resource ops.
+      // try_clone() would yield a copy containing the same
+      // underlying fd, so operations on the copy would also
+      // affect the one in resource table, and we don't need
+      // to write back.
+      let maybe_std_file_copy = std_file.try_clone();
+      // Insert the entry back with the same rid.
+      table.insert(
+        resource.rid,
+        Repr::FsFile(tokio_fs::File::from_std(std_file)),
+      );
+      if maybe_std_file_copy.is_err() {
+        return Box::new(futures::future::err(DenoError::from(
+          maybe_std_file_copy.unwrap_err(),
+        )));
+      }
+      let mut std_file_copy = maybe_std_file_copy.unwrap();
+      return Box::new(futures::future::lazy(move || {
+        let result = std_file_copy
+          .seek(seek_from)
+          .map(|_| {
+            return ();
+          }).map_err(DenoError::from);
+        futures::future::result(result)
+      }));
+    }
+    _ => panic!("cannot seek"),
+  }
+}