6 files changed, 119 insertions, 0 deletions
diff --git a/cli/js/deno_unstable.ts b/cli/js/deno_unstable.ts
index d8624c675..967eafdcd 100644
--- a/cli/js/deno_unstable.ts
+++ b/cli/js/deno_unstable.ts
@@ -4,6 +4,7 @@
 
 export { umask } from "./ops/fs/umask.ts";
 export { linkSync, link } from "./ops/fs/link.ts";
+export { fsyncSync, fsync } from "./ops/fs/sync.ts";
 export { symlinkSync, symlink } from "./ops/fs/symlink.ts";
 export { loadavg, osRelease, hostname } from "./ops/os.ts";
 export { openPlugin } from "./ops/plugins.ts";
diff --git a/cli/js/lib.deno.unstable.d.ts b/cli/js/lib.deno.unstable.d.ts
index 3339bfbac..daecf6604 100644
--- a/cli/js/lib.deno.unstable.d.ts
+++ b/cli/js/lib.deno.unstable.d.ts
@@ -1118,4 +1118,28 @@ declare namespace Deno {
    * ```
    */
   export function ftruncate(rid: number, len?: number): Promise<void>;
+
+  /** **UNSTABLE**: New API, yet to be vetted.
+   * Synchronously flushes any pending data and metadata operations of the given file stream to disk.
+   *  ```ts
+   * const file = Deno.openSync("my_file.txt", { read: true, write: true, create: true });
+   * Deno.writeSync(file.rid, new TextEncoder().encode("Hello World"));
+   * Deno.ftruncateSync(file.rid, 1);
+   * Deno.fsyncSync(file.rid);
+   * console.log(new TextDecoder().decode(Deno.readFileSync("my_file.txt"))); // H
+   * ```
+   */
+  export function fsyncSync(rid: number): void;
+
+  /** **UNSTABLE**: New API, yet to be vetted.
+   * Flushes any pending data and metadata operations of the given file stream to disk.
+   *  ```ts
+   * const file = await Deno.open("my_file.txt", { read: true, write: true, create: true });
+   * await Deno.write(file.rid, new TextEncoder().encode("Hello World"));
+   * await Deno.ftruncate(file.rid, 1);
+   * await Deno.fsync(file.rid);
+   * console.log(new TextDecoder().decode(await Deno.readFile("my_file.txt"))); // H
+   * ```
+   */
+  export function fsync(rid: number): Promise<void>;
 }
diff --git a/cli/js/ops/fs/sync.ts b/cli/js/ops/fs/sync.ts
new file mode 100644
index 000000000..5d5de7242
--- /dev/null
+++ b/cli/js/ops/fs/sync.ts
@@ -0,0 +1,10 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { sendSync, sendAsync } from "../dispatch_json.ts";
+
+export function fsyncSync(rid: number): void {
+  sendSync("op_fsync", { rid });
+}
+
+export async function fsync(rid: number): Promise<void> {
+  await sendAsync("op_fsync", { rid });
+}
diff --git a/cli/ops/fs.rs b/cli/ops/fs.rs
index 9ca4b31ae..9417c112d 100644
--- a/cli/ops/fs.rs
+++ b/cli/ops/fs.rs
@@ -22,6 +22,7 @@ use rand::{thread_rng, Rng};
 pub fn init(i: &mut CoreIsolate, s: &State) {
   i.register_op("op_open", s.stateful_json_op2(op_open));
   i.register_op("op_seek", s.stateful_json_op2(op_seek));
+  i.register_op("op_fsync", s.stateful_json_op2(op_fsync));
   i.register_op("op_umask", s.stateful_json_op(op_umask));
   i.register_op("op_chdir", s.stateful_json_op(op_chdir));
   i.register_op("op_mkdir", s.stateful_json_op(op_mkdir));
@@ -206,6 +207,50 @@ fn op_seek(
 }
 
 #[derive(Deserialize)]
+#[serde(rename_all = "camelCase")]
+struct FsyncArgs {
+  promise_id: Option<u64>,
+  rid: i32,
+}
+
+fn op_fsync(
+  isolate_state: &mut CoreIsolateState,
+  state: &State,
+  args: Value,
+  _zero_copy: &mut [ZeroCopyBuf],
+) -> Result<JsonOp, OpError> {
+  state.check_unstable("Deno.fsync");
+  let args: FsyncArgs = serde_json::from_value(args)?;
+  let rid = args.rid as u32;
+
+  let resource_table = isolate_state.resource_table.clone();
+  let is_sync = args.promise_id.is_none();
+
+  if is_sync {
+    let mut resource_table = resource_table.borrow_mut();
+    std_file_resource(&mut resource_table, rid, |r| match r {
+      Ok(std_file) => std_file.sync_all().map_err(OpError::from),
+      Err(_) => Err(OpError::type_error(
+        "cannot sync this type of resource".to_string(),
+      )),
+    })?;
+    Ok(JsonOp::Sync(json!({})))
+  } else {
+    let fut = async move {
+      let mut resource_table = resource_table.borrow_mut();
+      std_file_resource(&mut resource_table, rid, |r| match r {
+        Ok(std_file) => std_file.sync_all().map_err(OpError::from),
+        Err(_) => Err(OpError::type_error(
+          "cannot sync this type of resource".to_string(),
+        )),
+      })?;
+      Ok(json!({}))
+    };
+    Ok(JsonOp::Async(fut.boxed_local()))
+  }
+}
+
+#[derive(Deserialize)]
 struct UmaskArgs {
   mask: Option<u32>,
 }
diff --git a/cli/tests/unit/sync_test.ts b/cli/tests/unit/sync_test.ts
new file mode 100644
index 000000000..7a489e951
--- /dev/null
+++ b/cli/tests/unit/sync_test.ts
@@ -0,0 +1,38 @@
+// Copyright 2018-2020 the Deno authors. All rights reserved. MIT license.
+import { unitTest, assertEquals } from "./test_util.ts";
+
+unitTest(
+  { perms: { read: true, write: true } },
+  function fsyncSyncSuccess(): void {
+    const filename = Deno.makeTempDirSync() + "/test_fsyncSync.txt";
+    const file = Deno.openSync(filename, {
+      read: true,
+      write: true,
+      create: true,
+    });
+    const size = 64;
+    Deno.ftruncateSync(file.rid, size);
+    Deno.fsyncSync(file.rid);
+    assertEquals(Deno.statSync(filename).size, size);
+    Deno.close(file.rid);
+    Deno.removeSync(filename);
+  }
+);
+
+unitTest(
+  { perms: { read: true, write: true } },
+  async function fsyncSuccess(): Promise<void> {
+    const filename = (await Deno.makeTempDir()) + "/test_fsync.txt";
+    const file = await Deno.open(filename, {
+      read: true,
+      write: true,
+      create: true,
+    });
+    const size = 64;
+    await Deno.ftruncate(file.rid, size);
+    await Deno.fsync(file.rid);
+    assertEquals((await Deno.stat(filename)).size, size);
+    Deno.close(file.rid);
+    await Deno.remove(filename);
+  }
+);
diff --git a/cli/tests/unit/unit_tests.ts b/cli/tests/unit/unit_tests.ts
index b16141bdc..1701170d1 100644
--- a/cli/tests/unit/unit_tests.ts
+++ b/cli/tests/unit/unit_tests.ts
@@ -59,6 +59,7 @@ import "./streams_piping_test.ts";
 import "./streams_transform_test.ts";
 import "./streams_writable_test.ts";
 import "./symlink_test.ts";
+import "./sync_test.ts";
 import "./text_encoding_test.ts";
 import "./testing_test.ts";
 import "./timers_test.ts";