fs: add support for async iterators to fs.writeFile

Fixes: #38075

Author: HiroyukiYagihashi

doc/api/fs.md

@@ -3878,6 +3878,9 @@ details.
 <!-- YAML
 added: v0.1.29
 changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/38525
+    description: add support for async iterators to `fs.writeFile`.
   - version: v16.0.0
     pr-url: https://github.com/nodejs/node/pull/37460
     description: The error returned may be an `AggregateError` if more than one
@@ -3915,7 +3918,8 @@ changes:
 -->
 
 * `file` {string|Buffer|URL|integer} filename or file descriptor
-* `data` {string|Buffer|TypedArray|DataView|Object}
+* `data` {string|Buffer|TypedArray|DataView|Object
+  |AsyncIterable|Iterable|Stream}
 * `options` {Object|string}
   * `encoding` {string|null} **Default:** `'utf8'`
   * `mode` {integer} **Default:** `0o666`

lib/fs.js

@@ -85,6 +85,7 @@ const {
 const { FSReqCallback } = binding;
 const { toPathIfFileURL } = require('internal/url');
 const internalUtil = require('internal/util');
+const { isIterable } = require('internal/streams/utils');
 const {
   constants: {
     kIoMaxLength,
@@ -828,12 +829,12 @@ function write(fd, buffer, offset, length, position, callback) {
     } else {
       position = length;
     }
-    length = 'utf8';
+    length = length || 'utf8';
   }
 
   const str = String(buffer);
   validateEncoding(str, length);
-  callback = maybeCallback(position);
+  callback = maybeCallback(callback || position);
 
   const req = new FSReqCallback();
   req.oncomplete = wrapper;
@@ -2039,7 +2040,8 @@ function lutimesSync(path, atime, mtime) {
   handleErrorFromBinding(ctx);
 }
 
-function writeAll(fd, isUserFd, buffer, offset, length, signal, callback) {
+function writeAll(
+  fd, isUserFd, buffer, offset, length, signal, encoding, callback) {
   if (signal?.aborted) {
     const abortError = new AbortError();
     if (isUserFd) {
@@ -2051,7 +2053,29 @@ function writeAll(fd, isUserFd, buffer, offset, length, signal, callback) {
     }
     return;
   }
-  // write(fd, buffer, offset, length, position, callback)
+  if (isCustomIterable(buffer)) {
+    (async () => {
+      for await (const buf of buffer) {
+        fs.write(
+          fd, buf, undefined,
+          isArrayBufferView(buf) ? buf.byteLength : encoding,
+          null, (writeErr, _) => {
+            if (writeErr) {
+              if (isUserFd) {
+                callback(writeErr);
+              } else {
+                fs.close(fd, (err) => {
+                  callback(aggregateTwoErrors(err, writeErr));
+                });
+              }
+            }
+          }
+        );
+      }
+      fs.close(fd, callback);
+    })();
+    return;
+  }
   fs.write(fd, buffer, offset, length, null, (writeErr, written) => {
     if (writeErr) {
       if (isUserFd) {
@@ -2070,11 +2094,16 @@ function writeAll(fd, isUserFd, buffer, offset, length, signal, callback) {
     } else {
       offset += written;
       length -= written;
-      writeAll(fd, isUserFd, buffer, offset, length, signal, callback);
+      writeAll(
+        fd, isUserFd, buffer, offset, length, signal, encoding, callback);
     }
   });
 }
 
+function isCustomIterable(obj) {
+  return isIterable(obj) && !isArrayBufferView(obj) && typeof obj !== 'string';
+}
+
 /**
  * Asynchronously writes data to the file.
  * @param {string | Buffer | URL | number} path
@@ -2093,15 +2122,16 @@ function writeFile(path, data, options, callback) {
   options = getOptions(options, { encoding: 'utf8', mode: 0o666, flag: 'w' });
   const flag = options.flag || 'w';
 
-  if (!isArrayBufferView(data)) {
+  if (!isArrayBufferView(data) && !isCustomIterable(data)) {
     validateStringAfterArrayBufferView(data, 'data');
     data = Buffer.from(String(data), options.encoding || 'utf8');
   }
 
   if (isFd(path)) {
     const isUserFd = true;
     const signal = options.signal;
-    writeAll(path, isUserFd, data, 0, data.byteLength, signal, callback);
+    writeAll(path, isUserFd, data,
+             0, data.byteLength, signal, options.encoding, callback);
     return;
   }
 
@@ -2114,7 +2144,8 @@ function writeFile(path, data, options, callback) {
     } else {
       const isUserFd = false;
       const signal = options.signal;
-      writeAll(fd, isUserFd, data, 0, data.byteLength, signal, callback);
+      writeAll(fd, isUserFd, data,
+               0, data.byteLength, signal, options.encoding, callback);
     }
   });
 }

test/parallel/test-fs-write-file.js

@@ -24,6 +24,7 @@ const common = require('../common');
 const assert = require('assert');
 const fs = require('fs');
 const join = require('path').join;
+const { Readable } = require('stream');
 
 const tmpdir = require('../common/tmpdir');
 tmpdir.refresh();
@@ -95,3 +96,82 @@ fs.open(filename4, 'w+', common.mustSucceed((fd) => {
 
   process.nextTick(() => controller.abort());
 }
+
+{
+  const filenameIterable = join(tmpdir.path, 'testIterable.txt');
+  const iterable = {
+    expected: 'abc',
+    *[Symbol.iterator]() {
+      yield 'a';
+      yield 'b';
+      yield 'c';
+    }
+  };
+
+  fs.writeFile(filenameIterable, iterable, common.mustSucceed(() => {
+    const data = fs.readFileSync(filenameIterable, 'utf-8');
+    assert.strictEqual(iterable.expected, data);
+  }));
+}
+
+{
+  const filenameBufferIterable = join(tmpdir.path, 'testBufferIterable.txt');
+  const bufferIterable = {
+    expected: 'abc',
+    *[Symbol.iterator]() {
+      yield Buffer.from('a');
+      yield Buffer.from('b');
+      yield Buffer.from('c');
+    }
+  };
+
+  fs.writeFile(
+    filenameBufferIterable, bufferIterable, common.mustSucceed(() => {
+      const data = fs.readFileSync(filenameBufferIterable, 'utf-8');
+      assert.strictEqual(bufferIterable.expected, data);
+    })
+  );
+}
+
+
+{
+  const filenameAsyncIterable = join(tmpdir.path, 'testAsyncIterable.txt');
+  const asyncIterable = {
+    expected: 'abc',
+    *[Symbol.asyncIterator]() {
+      yield 'a';
+      yield 'b';
+      yield 'c';
+    }
+  };
+
+  fs.writeFile(filenameAsyncIterable, asyncIterable, common.mustSucceed(() => {
+    const data = fs.readFileSync(filenameAsyncIterable, 'utf-8');
+    assert.strictEqual(asyncIterable.expected, data);
+  }));
+}
+
+{
+  const filenameStream = join(tmpdir.path, 'testStream.txt');
+  const stream = Readable.from(['a', 'b', 'c']);
+  const expected = 'abc';
+
+  fs.writeFile(filenameStream, stream, common.mustSucceed(() => {
+    const data = fs.readFileSync(filenameStream, 'utf-8');
+    assert.strictEqual(expected, data);
+  }));
+}
+
+{
+  const filenameStreamWithEncoding =
+    join(tmpdir.path, 'testStreamWithEncoding.txt');
+  const stream = Readable.from(['ümlaut', ' ', 'sechzig']);
+  const expected = 'ümlaut sechzig';
+
+  fs.writeFile(
+    filenameStreamWithEncoding, stream, 'latin1', common.mustSucceed(() => {
+      const data = fs.readFileSync(filenameStreamWithEncoding, 'latin1');
+      assert.strictEqual(expected, data);
+    })
+  );
+}