feat(std/node): add writeBuffer of internal binding fs module (#888)

node/internal_binding/README.md

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+The modules in this directory implement (simulate) C++ bindings inplemented in
+src/ directory of Node.js
+
+These bindings are created in the node.js source code by using
+`NODE_MODULE_CONTEXT_AWARE_INTERNAL`.
+
+See:
+https://github.com/nodejs/node/blob/e46c680bf2b211bbd52cf959ca17ee98c7f657f5/src/README.md

node/internal_binding/fs.ts

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+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+import { assert } from "../../testing/asserts.ts";
+// This module implements functions in https://github.com/nodejs/node/blob/master/src/node_file.cc
+
+/**
+ * Write to the given file from the given buffer asynchronously.
+ *
+ * Implements async part of WriteBuffer in src/node_file.cc
+ * See: https://github.com/nodejs/node/blob/e9ed113/src/node_file.cc#L1818
+ *
+ * @param fs file descriptor
+ * @param buffer the data to write
+ * @param offset where in the buffer to start from
+ * @param length how much to write
+ * @param position if integer, position to write at in the file. if null, write from the current position
+ * @param callback callback function
+ */
+export function writeBuffer(
+  _fd: number,
+  _buffer: Uint8Array,
+  _offset: number,
+  _length: number,
+  _position: number | null,
+  _callback?: (err: Error, n: number) => void,
+): void {
+  throw new Error("unimplemented!");
+}
+
+/**
+ * Write to the given file from the given buffer synchronously.
+ *
+ * Implements sync part of WriteBuffer in src/node_file.cc
+ * See: https://github.com/nodejs/node/blob/e9ed113/src/node_file.cc#L1818
+ *
+ * @param fs file descriptor
+ * @param buffer the data to write
+ * @param offset where in the buffer to start from
+ * @param length how much to write
+ * @param position if integer, position to write at in the file. if null, write from the current position
+ * @param context context object for passing error number
+ */
+export function writeBufferSync(
+  fd: number,
+  buffer: Uint8Array,
+  offset: number,
+  length: number,
+  position: number | null,
+  ctx: { errno?: number },
+) {
+  assert(offset >= 0, "offset should be greater or equal to 0");
+  assert(
+    offset + length <= buffer.byteLength,
+    `buffer doesn't have enough data: byteLength = ${buffer.byteLength}, offset + length = ${offset +
+      length}`,
+  );
+  if (position) {
+    Deno.seekSync(fd, position, Deno.SeekMode.Current);
+  }
+  const subarray = buffer.subarray(offset, offset + length);
+  try {
+    return Deno.writeSync(fd, subarray);
+  } catch (e) {
+    ctx.errno = extractOsErrorNumberFromErrorMessage(e);
+    return 0;
+  }
+}
+
+function extractOsErrorNumberFromErrorMessage(e: Error): number {
+  const match = e.message.match(/\(os error (\d+)\)/);
+  if (match) {
+    return +match[1];
+  }
+  return 255; // Unknown error
+}

node/internal_binding/fs_test.ts

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+// Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
+import { writeBufferSync } from "./fs.ts";
+import { assertEquals } from "../../testing/asserts.ts";
+
+Deno.test("[node/internal_binding/fs] writeBufferSync", async () => {
+  const tempfile = await Deno.makeTempFile();
+  await Deno.writeTextFile(tempfile, "01234567890123456789");
+
+  const file = await Deno.open(tempfile, { write: true });
+  await Deno.seek(file.rid, 5, Deno.SeekMode.Start);
+
+  try {
+    const ctx: { errno?: number } = {};
+    const bytesWritten = writeBufferSync(
+      file.rid,
+      new Uint8Array([65, 66, 67, 68, 69] /* abcde */),
+      1,
+      3,
+      5,
+      ctx,
+    );
+
+    assertEquals(await Deno.readTextFile(tempfile), "0123456789BCD3456789");
+    assertEquals(bytesWritten, 3);
+    assertEquals(typeof ctx.errno, "undefined");
+  } finally {
+    Deno.close(file.rid);
+    await Deno.remove(tempfile);
+  }
+});
+Deno.test("[node/internal_binding/fs] writeBufferSync", async () => {
+  const tempfile = await Deno.makeTempFile();
+  await Deno.writeTextFile(tempfile, "01234567890123456789");
+  const file = await Deno.open(tempfile, { read: true, write: false });
+
+  try {
+    const ctx: { errno?: number } = {};
+    const bytesWritten = writeBufferSync(
+      file.rid,
+      new Uint8Array([65, 66, 67, 68, 69] /* abcde */),
+      1,
+      3,
+      5,
+      ctx,
+    );
+    assertEquals(bytesWritten, 0);
+    if (Deno.build.os === "windows") {
+      assertEquals(ctx.errno, 5); // Access is denied
+    } else {
+      assertEquals(ctx.errno, 9); // Bad file descriptor
+    }
+  } finally {
+    Deno.close(file.rid);
+    await Deno.remove(tempfile);
+  }
+});