fix: don't allow files to be nested inside other files

Resolves #1049

Fix issue with nested path write in `Volume` and add tests

Issue

The Volume class had an issue where files could incorrectly be nested inside other files. It was possible to read/write files nested inside other files which should not be allowed.

Solution

To resolve this issue, I updated the writeFileSync and readFileSync methods in the Volume class to check if the parent path of the file being written to is a file. If it is, we throw an ENOTDIR error. Additionally, we check if a path being read is a directory and throw an EISDIR error if so.

Changes Made

Updated writeFileSync in volume.ts:

writeFileSync(id: TFileId, data: TData, options?: opts.IWriteFileOptions): void {
    const opts = getWriteFileOptions(options);
    const flagsNum = flagsToNumber(opts.flag);
    const modeNum = modeToNumber(opts.mode);
    const buf = dataToBuffer(data, opts.encoding);

    // Check if the parent path is a file, and throw ENOTDIR error if so
    if (typeof id === 'string') {
        const parentPath = pathModule.dirname(id);
        if (this.existsSync(parentPath) && !this.statSync(parentPath).isDirectory()) {
            throw createError('ENOTDIR', 'writeFile', id);
        }
    }

    this.writeFileBase(id, buf, flagsNum, modeNum);
}

Updated `readFileSync` in `volume.ts`:

readFileSync(file: TFileId, options?: opts.IReadFileOptions | string): TDataOut {
    const opts = getReadFileOptions(options);
    const flagsNum = flagsToNumber(opts.flag);

    // Check if the path is a directory, and throw EISDIR error if so
    if (typeof file === 'string') {
        if (this.existsSync(file) && this.statSync(file).isDirectory()) {
            throw createError('EISDIR', 'readFile', file);
        }
    }

    return this.readFileBase(file, flagsNum, opts.encoding as BufferEncoding);
}

Added Tests

I added a new test file volume-issue.test.ts under src/tests/volume/ to cover these cases. They all pass:

import { Volume } from '../../volume';

describe('Volume issue tests', () => {
    let vol: Volume;

    beforeEach(() => {
        vol = new Volume();
    });

    test('should throw ENOTDIR error when writing to a nested path within a file', () => {
        vol.writeFileSync('/foo', 'hello');

        expect(() => {
            vol.writeFileSync('/foo/bar', 'world');
        }).toThrow(/ENOTDIR/);
    });

    test('should throw EISDIR error when trying to read a directory as a file', () => {
        vol.mkdirSync('/foo');

        expect(() => {
            vol.readFileSync('/foo');
        }).toThrow(/EISDIR/);
    });

    test('should read file contents correctly', () => {
        vol.writeFileSync('/foo', 'hello');
        const content = vol.readFileSync('/foo', 'utf8');
        expect(content).toBe('hello');
    });

    test('should throw ENOTDIR error when reading directory contents of a file', () => {
        vol.writeFileSync('/foo', 'hello');

        expect(() => {
            vol.readdirSync('/foo');
        }).toThrow(/ENOTDIR/);
    });
});

Thank you for allowing me to contribute to this project. I learned a lot, and if there is anything else that you need me to change, please let me know!

streamich / memfs