fix: handle chmod 0 permissions in existsSync and access methods

Co-authored-by: streamich <[email protected]>

Author: Copilot

src/node/__tests__/volume/chmod-permission-issue.test.ts

@@ -0,0 +1,78 @@
+import { create } from '../../../__tests__/util';
+
+describe('chmod 0 permission issue reproduction', () => {
+  // ❌ FAILURE - should return false but returns true
+  test('chmod on file and existsSync', () => {
+    // Arrange
+    const vol = create({ '/path/to/file.txt': 'some text' });
+    vol.chmodSync('/path/to/file.txt', 0o0000);
+
+    // Act
+    const exists = vol.existsSync('/path/to/file.txt');
+
+    // Assert
+    expect(exists).toBe(false);
+  });
+
+  // ✅ SUCCESS - this should already work
+  test('chmod on directory and existsSync', () => {
+    // Arrange
+    const vol = create({ '/path/to/file.txt': 'some text' });
+    vol.chmodSync('/path/to/', 0o0000);
+
+    // Act
+    const exists = vol.existsSync('/path/to/file.txt');
+
+    // Assert
+    expect(exists).toBe(false);
+  });
+
+  // ❌ FAILURE - should throw but doesn't throw
+  test.each([4 /* R_OK */, 2 /* W_OK */])('chmod on file and access mode %d', mode => {
+    // Arrange
+    const vol = create({ '/path/to/file.txt': 'some text' });
+    vol.chmodSync('/path/to/file.txt', 0o0000);
+
+    // Act & Assert
+    expect(() => {
+      vol.accessSync('/path/to/file.txt', mode);
+    }).toThrow();
+  });
+
+  // ✅ SUCCESS - this should already work
+  test.each([4 /* R_OK */, 2 /* W_OK */])('chmod on directory and access mode %d', mode => {
+    // Arrange
+    const vol = create({ '/path/to/file.txt': 'some text' });
+    vol.chmodSync('/path/to/', 0o0000);
+
+    // Act & Assert
+    expect(() => {
+      vol.accessSync('/path/to/file.txt', mode);
+    }).toThrow();
+  });
+
+  // F_OK should NOT throw - it just checks existence
+  test('chmod on file and access F_OK should not throw', () => {
+    const vol = create({ '/path/to/file.txt': 'some text' });
+    vol.chmodSync('/path/to/file.txt', 0o0000);
+
+    // F_OK should not throw - file exists
+    expect(() => {
+      vol.accessSync('/path/to/file.txt', 0 /* F_OK */);
+    }).not.toThrow();
+  });
+
+  // Test the exact scenario from the issue using promises API and fs constants
+  test('chmod on file and promises access with fs.constants', async () => {
+    const vol = create({ '/path/to/file.txt': 'some text' });
+    
+    await vol.promises.chmod('/path/to/file.txt', 0o0000);
+
+    // Should throw for R_OK and W_OK
+    await expect(vol.promises.access('/path/to/file.txt', 4 /* R_OK */)).rejects.toThrow();
+    await expect(vol.promises.access('/path/to/file.txt', 2 /* W_OK */)).rejects.toThrow();
+    
+    // F_OK should NOT throw - it just checks existence, which it does exist
+    await expect(vol.promises.access('/path/to/file.txt', 0 /* F_OK */)).resolves.toBeUndefined();
+  });
+});

src/node/volume.ts

@@ -74,6 +74,9 @@ const {
   O_DIRECTORY,
   O_SYMLINK,
   F_OK,
+  R_OK,
+  W_OK,
+  X_OK,
   COPYFILE_EXCL,
   COPYFILE_FICLONE_FORCE,
 } = constants;
@@ -872,7 +875,17 @@ export class Volume implements FsCallbackApi, FsSynchronousApi {
   };
 
   private _exists(filename: string): boolean {
-    return !!this._stat(filename);
+    try {
+      const link = this._core.getResolvedLinkOrThrow(filename, 'stat');
+      const node = link.getNode();
+
+      // For existsSync, Node.js returns false if the file exists but has no read permissions
+      // This matches the behavior described in the existing test comment
+      return node.canRead();
+    } catch (err) {
+      // If we can't find the file or access the path, it doesn't exist
+      return false;
+    }
   }
 
   public existsSync = (path: PathLike): boolean => {
@@ -896,8 +909,28 @@ export class Volume implements FsCallbackApi, FsSynchronousApi {
   };
 
   private _access(filename: string, mode: number) {
-    // TODO: Need to check mode?
-    this._core.getLinkOrThrow(filename, 'access');
+    const link = this._core.getLinkOrThrow(filename, 'access');
+    const node = link.getNode();
+
+    // F_OK (0) just checks for existence, which we already confirmed above
+    if (mode === F_OK) {
+      return;
+    }
+
+    // Check read permission
+    if (mode & R_OK && !node.canRead()) {
+      throw createError(ERROR_CODE.EACCES, 'access', filename);
+    }
+
+    // Check write permission
+    if (mode & W_OK && !node.canWrite()) {
+      throw createError(ERROR_CODE.EACCES, 'access', filename);
+    }
+
+    // Check execute permission
+    if (mode & X_OK && !node.canExecute()) {
+      throw createError(ERROR_CODE.EACCES, 'access', filename);
+    }
   }
 
   public accessSync = (path: PathLike, mode: number = F_OK) => {