fs: add recursive watch to linux

doc/api/fs.md

@@ -4377,10 +4377,6 @@ the returned {fs.FSWatcher}.
 The `fs.watch` API is not 100% consistent across platforms, and is
 unavailable in some situations.
 
-The recursive option is only supported on macOS and Windows.
-An `ERR_FEATURE_UNAVAILABLE_ON_PLATFORM` exception will be thrown
-when the option is used on a platform that does not support it.
-
 On Windows, no events will be emitted if the watched directory is moved or
 renamed. An `EPERM` error is reported when the watched directory is deleted.
 

lib/fs.js

@@ -57,6 +57,7 @@ const {
 
 const pathModule = require('path');
 const { isArrayBufferView } = require('internal/util/types');
+const linuxWatcher = require('internal/fs/linux_recursive_watcher');
 
 // We need to get the statValues from the binding at the callsite since
 // it's re-initialized after deserialization.
@@ -68,7 +69,6 @@ const {
   codes: {
     ERR_FS_FILE_TOO_LARGE,
     ERR_INVALID_ARG_VALUE,
-    ERR_FEATURE_UNAVAILABLE_ON_PLATFORM,
   },
   AbortError,
   uvErrmapGet,
@@ -161,7 +161,7 @@ let FileReadStream;
 let FileWriteStream;
 
 const isWindows = process.platform === 'win32';
-const isOSX = process.platform === 'darwin';
+const isLinux = process.platform === 'linux';
 
 
 function showTruncateDeprecation() {
@@ -2297,13 +2297,22 @@ function watch(filename, options, listener) {
 
   if (options.persistent === undefined) options.persistent = true;
   if (options.recursive === undefined) options.recursive = false;
-  if (options.recursive && !(isOSX || isWindows))
-    throw new ERR_FEATURE_UNAVAILABLE_ON_PLATFORM('watch recursively');
-  const watcher = new watchers.FSWatcher();
-  watcher[watchers.kFSWatchStart](filename,
-                                  options.persistent,
-                                  options.recursive,
-                                  options.encoding);
+
+  let watcher;
+
+  // TODO(anonrig): Remove this when/if libuv supports it.
+  // libuv does not support recursive file watch on Linux due to
+  // the limitations of inotify.
+  if (options.recursive && isLinux) {
+    watcher = new linuxWatcher.FSWatcher(options);
+    watcher[linuxWatcher.kFSWatchStart](filename);
+  } else {
+    watcher = new watchers.FSWatcher();
+    watcher[watchers.kFSWatchStart](filename,
+                                    options.persistent,
+                                    options.recursive,
+                                    options.encoding);
+  }
 
   if (listener) {
     watcher.addListener('change', listener);

lib/internal/fs/linux_recursive_watcher.js

@@ -0,0 +1,154 @@
+'use strict';
+
+const { EventEmitter } = require('events');
+const path = require('path');
+const { Symbol, ObjectKeys } = primordials;
+
+const kFSWatchStart = Symbol('kFSWatchStart');
+
+let internalSync;
+let internalPromises;
+
+function lazyLoadFsPromises() {
+  internalPromises ??= require('fs/promises');
+  return internalPromises;
+}
+
+function lazyLoadFsSync() {
+  internalSync ??= require('fs');
+  return internalSync;
+}
+
+async function traverse(dir, files = {}) {
+  const { stat, readdir } = lazyLoadFsPromises();
+
+  files[dir] = await stat(dir);
+
+  try {
+    const directoryFiles = await readdir(dir);
+
+    for (const file of directoryFiles) {
+      const f = path.join(dir, file);
+
+      try {
+        const stats = await stat(f);
+
+        files[f] = stats;
+
+        if (stats.isDirectory()) {
+          await traverse(f, files);
+        }
+      } catch (error) {
+        if (error.code !== 'ENOENT' || error.code !== 'EPERM') {
+          throw error;
+        }
+      }
+
+    }
+  } catch (error) {
+    if (error.code !== 'EACCES') {
+      throw error;
+    }
+  }
+
+  return files;
+}
+
+class FSWatcher extends EventEmitter {
+  #options = null;
+  #closed = false;
+  #files = {};
+
+  /**
+   * @param {{
+   *   persistent?: boolean;
+   *   recursive?: boolean;
+   *   encoding?: string;
+   *   signal?: AbortSignal;
+   *   }} [options]
+   */
+  constructor(options) {
+    super();
+
+    this.#options = options || {};
+  }
+
+  async close() {
+    const { unwatchFile } = lazyLoadFsPromises();
+    this.#closed = true;
+
+    for (const file of ObjectKeys(this.#files)) {
+      await unwatchFile(file);
+    }
+
+    this.emit('close');
+  }
+
+  /**
+   * @param {string} file
+   */
+  #watchFile(file) {
+    const { readdir } = lazyLoadFsPromises();
+    const { stat, watchFile } = lazyLoadFsSync();
+
+    watchFile(file, this.#options, (event, payload) => {
+      const existingStat = this.#files[file];
+
+      if (existingStat && !existingStat.isDirectory() &&
+        event.nlink !== 0 && existingStat.mtime.getTime() === event.mtime.getTime()) {
+        return;
+      }
+
+      this.#files[file] = event;
+
+      if (!event.isDirectory()) {
+        this.emit(event, payload);
+      } else {
+          readdir(file)
+          .then((files) => {
+            for (const subfile of files) {
+              const f = path.join(file, subfile);
+
+              if (!this.#files[f]) {
+                stat(f, (error, stat) => {
+                  if (error) {
+                    return;
+                  }
+
+                  this.#files[f] = stat;
+                  this.#watchFile(f);
+                });
+              }
+            }
+          });
+      }
+    });
+  }
+
+  /**
+   * @param {string | Buffer | URL} filename
+   */
+  async [kFSWatchStart](filename) {
+    this.#closed = false;
+    this.#files = await traverse(filename);
+
+    this.#watchFile(filename);
+
+    for (const f in this.#files) {
+      this.#watchFile(f);
+    }
+  }
+
+  /**
+   * @param {string} name
+   * @param {Function=} callback
+   */
+  addEventListener(name, callback) {
+    this.on(name, (...args) => callback(...args));
+  }
+}
+
+module.exports = {
+  FSWatcher,
+  kFSWatchStart,
+};

test/parallel/test-fs-watch-recursive.js

@@ -17,12 +17,6 @@ tmpdir.refresh();
 const testsubdir = fs.mkdtempSync(testDir + path.sep);
 const relativePathOne = path.join(path.basename(testsubdir), filenameOne);
 const filepathOne = path.join(testsubdir, filenameOne);
-
-if (!common.isOSX && !common.isWindows) {
-  assert.throws(() => { fs.watch(testDir, { recursive: true }); },
-                { code: 'ERR_FEATURE_UNAVAILABLE_ON_PLATFORM' });
-  return;
-}
 const watcher = fs.watch(testDir, { recursive: true });
 
 let watcherClosed = false;