Add copyFile/copyFileSync (#863)

js/copy_file.ts

@@ -0,0 +1,46 @@
+// Copyright 2018 the Deno authors. All rights reserved. MIT license.
+import * as fbs from "gen/msg_generated";
+import { flatbuffers } from "flatbuffers";
+import * as dispatch from "./dispatch";
+
+/**
+ * Copies the contents of a file to another by name synchronously.
+ * Creates a new file if target does not exists, and if target exists,
+ * overwrites original content of the target file.
+ * It would also copy the permission of the original file
+ * to the destination.
+ *
+ *     import { copyFileSync } from "deno";
+ *     copyFileSync("from.txt", "to.txt");
+ */
+export function copyFileSync(from: string, to: string): void {
+  dispatch.sendSync(...req(from, to));
+}
+
+/**
+ * Copies the contents of a file to another by name.
+ * Creates a new file if target does not exists, and if target exists,
+ * overwrites original content of the target file.
+ * It would also copy the permission of the original file
+ * to the destination.
+ *
+ *     import { copyFile } from "deno";
+ *     await copyFile("from.txt", "to.txt");
+ */
+export async function copyFile(from: string, to: string): Promise<void> {
+  await dispatch.sendAsync(...req(from, to));
+}
+
+function req(
+  from: string,
+  to: string
+): [flatbuffers.Builder, fbs.Any, flatbuffers.Offset] {
+  const builder = new flatbuffers.Builder();
+  const from_ = builder.createString(from);
+  const to_ = builder.createString(to);
+  fbs.CopyFile.startCopyFile(builder);
+  fbs.CopyFile.addFrom(builder, from_);
+  fbs.CopyFile.addTo(builder, to_);
+  const msg = fbs.CopyFile.endCopyFile(builder);
+  return [builder, fbs.Any.CopyFile, msg];
+}