fs: fix bufferSize option for opendir recursive

The bufferSize option was not respected in recursive mode. This PR
implements a naive solution to fix this issue until a better
implementation can be designed.

Fixes: nodejs#48820

lib/internal/fs/dir.js

@@ -164,12 +164,16 @@ class Dir {
       return;
     }
 
-    const result = handle.read(
+    // Fully read the directory and buffer the entries.
+    // This is a naive solution and for very large sub-directories
+    // it can even block the event loop. Essentially, `bufferSize` is
+    // not respected for recursive mode. This is a known limitation.
+    // Issue to fix: https://github.com/nodejs/node/issues/55764
+    let result;
+    while ((result = handle.read(
       this.#options.encoding,
       this.#options.bufferSize,
-    );
-
-    if (result) {
+    ))) {
       this.processReadResult(path, result);
     }
 

test/sequential/test-fs-opendir-recursive.js

@@ -132,6 +132,7 @@ function getDirentPath(dirent) {
 }
 
 function assertDirents(dirents) {
+  assert.strictEqual(dirents.length, expected.length);
   dirents.sort((a, b) => (getDirentPath(a) < getDirentPath(b) ? -1 : 1));
   assert.deepStrictEqual(
     dirents.map((dirent) => {
@@ -221,3 +222,21 @@ function processDirCb(dir, cb) {
 
   test().then(common.mustCall());
 }
+
+// Issue https://github.com/nodejs/node/issues/48820 highlights that
+// opendir recursive does not properly handle the buffer size option.
+// This test asserts that the buffer size option is respected.
+{
+  const dir = fs.opendirSync(testDir, { bufferSize: 1, recursive: true });
+  processDirSync(dir);
+  dir.closeSync();
+}
+
+{
+  fs.opendir(testDir, { recursive: true, bufferSize: 1 }, common.mustSucceed((dir) => {
+    processDirCb(dir, common.mustSucceed((dirents) => {
+      assertDirents(dirents);
+      dir.close(common.mustSucceed());
+    }));
+  }));
+}